View source for Electron

{{Short description|Elementary particle with negative charge}}
{{Other uses}}
{{pp-move|small=yes}}
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{{Infobox particle
|name            = Electron
|image           = Atomic-orbital-clouds spd m0.png |image_size = 280px
|caption         = Hydrogen [[atomic orbital]]s at different energy levels. The more opaque areas are where one is most likely to find an electron at any given time.
|num_types       =
|composition     = [[Elementary particle]]<ref name=prl50/>
|statistics      = [[Fermion]]ic
|group           = [[Lepton]]
|generation      = First
|interaction     = [[Weak interaction|Weak]], [[Electromagnetic interaction|electromagnetic]], [[Gravitation|gravity]] 
|antiparticle    = [[Positron]]{{efn|The positron is occasionally called the 'anti-electron'.}}
|theorized       = [[Richard Laming]] (1838–1851),<ref name=farrar/><br/>[[George Johnstone Stoney|G. Johnstone Stoney]] (1874) and others.<ref name=arabatzis/><ref name=buchwald1/>
|discovered      = [[J. J. Thomson]] (1897)<ref name=thomson/>
|symbol          = {{SubatomicParticle|Electron}}, {{SubatomicParticle|beta-}}
|mass            = {{physconst|me}}<br/>{{physconst|me_Da}}<br/> [{{val|1822.888486209|(53)}}]<sup>−1</sup>&nbsp;Da{{efn|The fractional version's denominator is the inverse of the decimal value (along with its relative standard uncertainty of {{val|2.9|e=-11}}).}}<br/>{{physconst|mec2_MeV|unit=no|after=&nbsp;{{val|ul=MeV/c2}}}}
|electric_charge = {{val|-1|ul=e}}<br/> −{{physconst|e}}
|magnetic_moment = {{physconst|mue}}<br/>{{val|-1.00115965218128|(18)|u=[[Bohr magneton|''μ''<sub>B</sub>]]}}<ref>{{cite web |url=https://physics.nist.gov/cgi-bin/cuu/Value?muemsmub |title=2018 CODATA Value: electron magnetic moment to Bohr magneton ratio |date=20 May 2019 |work=The NIST Reference on Constants, Units, and Uncertainty |publisher=[[National Institute of Standards and Technology|NIST]] |access-date=2022-11-15 |archive-date=2000-12-02 |archive-url=https://web.archive.org/web/20001202075600/https://physics.nist.gov/cgi-bin/cuu/Value?muemsmub |url-status=live }}</ref>
|spin            = {{sfrac| 1 |2}}&nbsp;[[reduced Planck constant|''ħ'']]
|weak_isospin    = {{nowrap|[[Chirality (physics)|LH]]: −{{sfrac| 1 |2}}, [[Chirality (physics)|RH]]: 0}}
|weak_hypercharge= {{nowrap|[[Chirality (physics)|LH]]: −1, [[Chirality (physics)|RH]]: −2}}
| mean_lifetime   = > {{val|6.6|e=28|u=years}}<ref name=bx2015>
 {{cite journal
  | last1= Agostini |first1=M.
  | display-authors=etal
  | collaboration=[[Borexino]] Collaboration
  | year = 2015
  | title = Test of electric charge conservation with Borexino
  | journal = [[Physical Review Letters]]
  | volume = 115 | issue = 23 | page = 231802
  | doi = 10.1103/PhysRevLett.115.231802
  | bibcode =  2015PhRvL.115w1802A
  | arxiv = 1509.01223
  | pmid = 26684111
  | s2cid = 206265225
 }}</ref> (stable)
}}
{{Standard model of particle physics}}

The '''electron''' ('''{{SubatomicParticle|Electron}}''', or '''{{SubatomicParticle|beta-}}''' in nuclear reactions) is a [[subatomic particle]] with a negative one [[elementary charge|elementary electric charge]].<ref>
{{cite web
 |last=Coffey |first=Jerry
 |date=2010-09-10
 |title=What is an electron?
 |url=https://www.universetoday.com/73323/what-is-an-electron/
 |access-date=10 September 2010 |url-status=live
 |archive-url=https://web.archive.org/web/20121111231002/http://www.universetoday.com/73323/what-is-an-electron/
 |archive-date=2012-11-11 |df=dmy-all
}}
</ref> Electrons belong to the first [[generation (particle physics)|generation]] of the [[lepton]] particle family,<ref name="curtis74">
{{cite book
 | last = Curtis | first = L.J.
 | year = 2003
 | title = Atomic Structure and Lifetimes: A conceptual approach
 | page = 74
 | publisher = Cambridge University Press
 | isbn = 978-0-521-53635-6
 | url = https://books.google.com/books?id=KmwCsuvxClAC&pg=PA74
 | access-date = 2020-08-25 | url-status = live
 | archive-url = https://web.archive.org/web/20200316220442/https://books.google.com/books?id=KmwCsuvxClAC&pg=PA74
 | archive-date = 2020-03-16
}}
</ref> and are generally thought to be [[elementary particle]]s because they have no known components or substructure.<ref name="prl50" /> The electron's [[Invariant mass|mass]] is approximately [[Proton-to-electron mass ratio|1/1836]] that of the [[proton]].<ref name="nist_codata_mu" /> [[Quantum mechanics|Quantum mechanical]] properties of the electron include an intrinsic [[angular momentum]] ([[spin (physics)|spin]]) of a half-integer value, expressed in units of the [[Planck constant#Reduced Planck constant|reduced Planck constant]], {{mvar|ħ}}. Being [[fermion]]s, no two electrons can occupy the same [[quantum state]], per the [[Pauli exclusion principle]].<ref name=curtis74/> Like all elementary particles, electrons exhibit properties of [[wave–particle duality|both particles and waves]]: They can collide with other particles and can be [[electron diffraction|diffracted]] like light. The [[#Quantum properties|wave properties of electrons]] are easier to observe with experiments than those of other particles like [[neutron]]s and protons because electrons have a lower mass and hence a longer [[de Broglie wavelength]] for a given energy.

Electrons play an essential role in numerous [[physics|physical]] phenomena, such as [[electricity]], [[magnetism]], [[chemistry]], and [[thermal conductivity]]; they also participate in [[gravitational wave|gravitational]], [[Lorentz force|electromagnetic]], and [[weak interaction]]s.<ref name="anastopoulos1" /> Since an electron has charge, it has a surrounding [[electric field]]; if that electron is moving relative to an observer, the observer will observe it to generate a [[magnetic field]]. Electromagnetic fields produced from other sources will affect the motion of an electron according to the [[Lorentz force law]]. Electrons radiate or absorb energy in the form of [[photon]]s when they are accelerated.

Laboratory instruments are capable of trapping individual electrons as well as [[Plasma (physics)|electron plasma]] by the use of electromagnetic fields. Special [[telescope]]s can detect electron plasma in outer space. Electrons are involved in many applications, such as [[tribology]] or frictional charging, electrolysis, electrochemistry, battery technologies, [[electronics]], [[Electron beam welding|welding]], [[cathode-ray tube]]s, photoelectricity, photovoltaic solar panels, [[electron microscope]]s, [[radiation therapy]], [[Free-electron laser|lasers]], [[gaseous ionization detectors]], and [[particle accelerator]]s.

Interactions involving electrons with other subatomic particles are of interest in fields such as [[chemistry]] and [[nuclear physics]]. The [[Coulomb's law|Coulomb force]] interaction between the positive [[proton]]s within [[atomic nucleus|atomic nuclei]] and the negative electrons without allows the composition of the two known as [[atom]]s. Ionization or differences in the proportions of negative electrons versus positive nuclei changes the [[binding energy]] of an atomic system. The exchange or sharing of the electrons between two or more atoms is the main cause of [[chemical bond]]ing.<ref name=Pauling />

In 1838, British natural philosopher [[Richard Laming]] first hypothesized the concept of an indivisible quantity of electric charge to explain the [[Chemical property|chemical properties]] of atoms.<ref name="arabatzis" /> Irish physicist [[George Johnstone Stoney]] named this charge "electron" in 1891, and [[J. J. Thomson]] and his team of British physicists identified it as a particle in 1897 during the [[cathode ray|cathode-ray tube experiment]].<ref name="thomson" /> 

Electrons participate in [[nuclear reaction]]s, such as [[stellar nucleosynthesis|nucleosynthesis in stars]], where they are known as [[beta particle]]s. Electrons can be created through [[beta decay]] of [[Radionuclide|radioactive isotopes]] and in high-energy collisions, for instance, when [[cosmic ray]]s enter the atmosphere.  The [[antiparticle]] of the electron is called the [[positron]]; it is identical to the electron, except that it carries electrical [[charge (physics)|charge]] of the opposite sign. When an [[Electron–positron annihilation|electron collides with a positron]], both particles can be [[annihilation|annihilated]], producing [[gamma ray]] [[photon]]s.

== History ==
{{See also|History of electromagnetic theory|label 1=History of electromagnetism}}

=== Discovery of effect of electric force ===
The [[Ancient Greece#Science and technology|ancient Greeks]] noticed that [[amber]] attracted small objects when rubbed with fur. Along with [[lightning]], this phenomenon is one of humanity's earliest recorded experiences with [[Electricity#History|electricity]].<ref name="DictOrigins" /> In his 1600 treatise {{lang|la|[[De Magnete]]}}, the English scientist [[William Gilbert (astronomer)|William Gilbert]] coined the [[Neo-Latin]] term {{lang|la|electrica}}, to refer to those substances with property similar to that of amber which attract small objects after being rubbed.<ref name=Benjamin>
{{citation
 | last=Benjamin
 | first=Park
 | title=A history of electricity (The intellectual rise in electricity) from antiquity to the days of Benjamin Franklin
 | place=New York
 | publisher=J. Wiley
 | year=1898
 | pages=315, 484–5
 | url=https://archive.org/details/cu31924004128686/page/n10
 | isbn=978-1-313-10605-4
}}</ref> Both ''electric'' and ''electricity'' are derived from the Latin ''{{lang|la|ēlectrum}}'' (also the root of the [[electrum|alloy of the same name]]), which came from the [[Ancient Greek|Greek]] word for amber, {{lang|grc|ἤλεκτρον}} (''{{lang|grc-Latn|ēlektron}}'').

=== Discovery of two kinds of charges ===
In the early 1700s, French chemist [[Charles François de Cisternay du Fay|Charles François du Fay]] found that if a charged gold-leaf is repulsed by glass rubbed with silk, then the same charged gold-leaf is attracted by amber rubbed with wool. From this and other results of similar types of experiments, du Fay concluded that electricity consists of two [[Aether theories|electrical fluids]], ''vitreous'' fluid from glass rubbed with silk and ''resinous'' fluid from amber rubbed with wool.  These two fluids can neutralize each other when combined.<ref name=Benjamin /><ref>
{{cite book
 | last = Keithley
 | first = J.F.
 | year = 1999
 | title = The Story of Electrical and Magnetic Measurements: From 500 B.C. to the 1940s
 | url = https://books.google.com/books?id=uwgNAtqSHuQC&pg=PR7
 | publisher = [[IEEE|IEEE Press]]
 | pages = 19–20
 | isbn = 978-0-7803-1193-0
 | access-date = 2020-08-25
 | archive-date = 2022-02-04
 | archive-url = https://web.archive.org/web/20220204082420/https://books.google.com/books?id=uwgNAtqSHuQC&pg=PR7
 | url-status = live
}}</ref> American scientist [[Ebenezer Kinnersley]] later also independently reached the same conclusion.<ref name="Cajori1917">
{{cite book
 |first=Florian |last=Cajori
 |title=A History of Physics in Its Elementary Branches: Including the Evolution of Physical Laboratories
 |url=https://archive.org/details/historyofphysics00cajo
 |year=1917 |publisher=Macmillan}}</ref>{{rp|118}} A decade later [[Benjamin Franklin]] proposed that electricity was not from different types of electrical fluid, but a single electrical fluid showing an excess (+) or deficit (−). He gave them the modern [[electric charge|charge]] nomenclature of positive and negative respectively.<ref>{{cite web
 | title = Benjamin Franklin (1706–1790)
 | url = https://scienceworld.wolfram.com/biography/FranklinBenjamin.html
 | work = [[ScienceWorld|Eric Weisstein's World of Biography]]
 | publisher = [[Wolfram Research]]
 | access-date = 2010-12-16
 | df = dmy-all
 | archive-date = 2013-08-27
 | archive-url = https://web.archive.org/web/20130827114343/http://scienceworld.wolfram.com/biography/FranklinBenjamin.html
 | url-status = live
}}</ref> Franklin thought of the charge carrier as being positive, but he did not correctly identify which situation was a surplus of the charge carrier, and which situation was a deficit.<ref>
{{cite book
 |last1=Myers | first1 = R.L.
 | year = 2006
 | title = The Basics of Physics
 | url = https://archive.org/details/basicsofphysics0000myer/page/242
 |url-access=registration
 | publisher = [[Greenwood Publishing Group]]
 | page=242
 | isbn = 978-0-313-32857-2
}}</ref>

Between 1838 and 1851, British natural philosopher [[Richard Laming]] developed the idea that an atom is composed of a core of matter surrounded by subatomic particles that had unit [[electric charge]]s.<ref name="farrar">
{{cite journal
 | last = Farrar | first = W.V.
 | year = 1969
 | title = Richard Laming and the Coal-Gas Industry, with His Views on the Structure of Matter
 | journal = [[Annals of Science]]
 | volume = 25 | pages = 243–254
 | doi =10.1080/00033796900200141
 | issue = 3
}}</ref> Beginning in 1846, German physicist [[Wilhelm Eduard Weber]] theorized that electricity was composed of positively and negatively charged fluids, and their interaction was governed by the [[Inverse-square law|inverse square law]]. After studying the phenomenon of [[electrolysis]] in 1874, Irish physicist [[George Johnstone Stoney]] suggested that there existed a "single definite quantity of electricity", the charge of a [[Valence (chemistry)|monovalent]] [[ion]]. He was able to estimate the value of this elementary charge ''e'' by means of [[Faraday's laws of electrolysis]].<ref>
{{cite journal
 | last = Barrow | first = J.D.
 | year = 1983
 | title = Natural Units Before Planck
 | journal = [[Astronomy & Geophysics|Quarterly Journal of the Royal Astronomical Society]]
 | volume = 24 | pages = 24–26
 | bibcode = 1983QJRAS..24...24B
}}</ref> However, Stoney believed these charges were permanently attached to atoms and could not be removed. In 1881, German physicist [[Hermann von Helmholtz]] argued that both positive and negative charges were divided into elementary parts, each of which "behaves like atoms of electricity".<ref name="arabatzis">
{{cite book
 | last = Arabatzis
 | first = T.
 | year = 2006
 | title = Representing Electrons: A Biographical Approach to Theoretical Entities
 | url = https://books.google.com/books?id=rZHT-chpLmAC&pg=PA70
 | pages = 70–74, 96
 | publisher = University of Chicago Press
 | isbn = 978-0-226-02421-9
 | access-date = 2020-08-25
 | archive-date = 2021-01-07
 | archive-url = https://web.archive.org/web/20210107160308/https://books.google.com/books?id=rZHT-chpLmAC&pg=PA70
 | url-status = live
}}</ref>

Stoney initially coined the term ''electrolion'' in 1881. Ten years later, he switched to ''electron'' to describe these elementary charges, writing in 1894: "... an estimate was made of the actual amount of this most remarkable fundamental unit of electricity, for which I have since ventured to suggest the name ''electron''". A 1906 proposal to change to ''electrion'' failed because [[Hendrik Lorentz]] preferred to keep ''electron''.<ref>
{{cite book
 | first=Sōgo
 | last=Okamura
 | title=History of Electron Tubes
 | url=https://books.google.com/books?id=VHFyngmO95YC&pg=PR11
 | access-date=29 May 2015
 | year=1994
 | publisher=IOS Press
 | isbn=978-90-5199-145-1
 | page=11
 | quote=In 1881, Stoney named this electromagnetic 'electrolion'. It came to be called 'electron' from 1891. [...] In 1906, the suggestion to call cathode ray particles 'electrions' was brought up but through the opinion of Lorentz of Holland 'electrons' came to be widely used.
 | archive-date=11 May 2016
 | archive-url=https://web.archive.org/web/20160511214552/https://books.google.com/books?id=VHFyngmO95YC&pg=PR11
 | url-status=live
}}</ref><ref name="GJStoney">
{{cite journal
 | last = Stoney
 | first = G.J.
 | year = 1894
 | title = Of the "Electron," or Atom of Electricity
 | journal = [[Philosophical Magazine]]
 | volume = 38
 | issue = 5
 | pages = 418–420
 | doi = 10.1080/14786449408620653
 | url = https://zenodo.org/record/1431209
 | access-date = 2019-08-25
 | archive-date = 2020-10-31
 | archive-url = https://web.archive.org/web/20201031080323/https://zenodo.org/record/1431209
 | url-status = live
}}</ref> The word ''electron'' is a combination of the words ''<u>electr</u>ic'' and ''i<u>on</u>''.<ref>"electron, n.2". OED Online. March 2013. Oxford University Press. Accessed 12 April 2013 [https://www.oed.com/view/Entry/60302?rskey=owKYbt&result=2] {{Webarchive|url=https://web.archive.org/web/20210427080603/https://www.oed.com/view/Entry/60302?rskey=owKYbt&result=2|date=2021-04-27}}</ref> The suffix [[wikt:-on|-''on'']] which is now used to designate other subatomic particles, such as a proton or neutron, is in turn derived from electron.<ref>
{{cite book
 | editor-last = Soukhanov | editor-first = A.H.
 | year = 1986
 | title = Word Mysteries & Histories
 | page = 73
 | publisher = Houghton Mifflin
 | isbn = 978-0-395-40265-8
}}</ref><ref>
{{cite book
 | editor-last = Guralnik | editor-first = D.B.
 | year = 1970
 | title = Webster's New World Dictionary
 | publisher = Prentice Hall
 | page = 450
}}</ref>

=== Discovery of free electrons outside matter ===
{{see also|J. J. Thomson#Discovery of the electron}}

[[File:Cyclotron motion wider view.jpg|right|thumb|alt=A round glass vacuum tube with a glowing circular beam inside|A beam of electrons deflected by a magnetic field into a circle<ref>
{{cite book
 | last1 = Born
 | first1 = M.
 | last2 = Blin-Stoyle
 | first2 = R.J.
 | last3 = Radcliffe
 | first3 = J.M.
 | year = 1989
 | title = Atomic Physics
 | url = https://books.google.com/books?id=NmM-KujxMtoC&pg=PA26
 | page = 26
 | publisher = [[Courier Dover]]
 | isbn = 978-0-486-65984-8
 | access-date = 2020-08-25
 | archive-date = 2021-01-26
 | archive-url = https://web.archive.org/web/20210126003322/https://books.google.com/books?id=NmM-KujxMtoC&pg=PA26
 | url-status = live
}}</ref>]]

While studying electrical conductivity in [[rarefied]] gases in 1859, the German physicist [[Julius Plücker]] observed the radiation emitted from the cathode caused phosphorescent light to appear on the tube wall near the cathode; and the region of the phosphorescent light could be moved by application of a magnetic field.<ref>{{Cite journal|last=Plücker|first=M.|date=1858-12-01|title=XLVI. Observations on the electrical discharge through rarefied gases|url=https://doi.org/10.1080/14786445808642591|journal=The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science|volume=16|issue=109|pages=408–418|doi=10.1080/14786445808642591|issn=1941-5982}}</ref>  In 1869, Plücker's student [[Johann Wilhelm Hittorf]] found that a solid body placed in between the cathode and the phosphorescence would cast a shadow upon the phosphorescent region of the tube. Hittorf inferred that there are straight rays emitted from the cathode and that the phosphorescence was caused by the rays striking the tube walls. Furthermore, he also discovered that these rays are deflected by magnets just like lines of current.<ref>{{Cite book |last=Darrigol |first=Olivier |url=https://books.google.com/books?id=ysMf2pAid94C&pg=PA277 |title=Electrodynamics from Ampère to Einstein |date=2003 |publisher=OUP Oxford |isbn=978-0-19-850593-8 |language=en}}</ref>

In 1876, the German physicist [[Eugen Goldstein]] showed that the rays were emitted perpendicular to the cathode surface, which distinguished between the rays that were emitted from the cathode and the incandescent light.  Goldstein dubbed the rays [[cathode ray]]s.<ref name="leicester" /><ref name="Whittaker">
{{cite book
 |last=Whittaker
 |first=E.T.
 |author-link=E. T. Whittaker
 |title=[[A History of the Theories of Aether and Electricity]]
 |volume=1
 |publisher=Nelson |place=London
 |year=1951
}}</ref>{{rp|393}} Decades of experimental and theoretical research involving cathode rays were important in [[J. J. Thomson]]'s eventual discovery of electrons.<ref name="arabatzis" /> Goldstein also experimented with double cathodes and hypothesized that one ray may repulse another, although he didn't believe that any particles might be involved.<ref name=":0">{{Cite journal |last=Thomson |first=George |date=1970 |title=An Unfortunate Experiment: Hertz and the Nature of Cathode Rays |url=https://www.jstor.org/stable/530878 |journal=Notes and Records of the Royal Society of London |volume=25 |issue=2 |pages=237–242 |doi=10.1098/rsnr.1970.0032 |jstor=530878 |issn=0035-9149}}</ref>

During the 1870s, the English chemist and physicist Sir [[William Crookes]] developed the first cathode-ray tube to have a [[vacuum|high vacuum]] inside.<ref name="dekosky">
{{cite journal
 | last = DeKosky | first = R.K.
 | year = 1983
 | title = William Crookes and the quest for absolute vacuum in the 1870s
 | journal = [[Annals of Science]]
 | volume = 40 | issue = 1 | pages = 1–18
 | doi =10.1080/00033798300200101
}}</ref> He then showed in 1874 that the cathode rays can turn a small paddle wheel when placed in their path.  Therefore, he concluded that the rays carried momentum. Furthermore, by applying a magnetic field, he was able to deflect the rays, thereby demonstrating that the beam behaved as though it were negatively charged.<ref name="leicester">
{{cite book
 | last = Leicester
 | first = H.M.
 | year = 1971
 | title = The Historical Background of Chemistry
 | url = https://books.google.com/books?id=aJZVQnqcwv4C&pg=PA221
 | pages = 221–222
 | publisher = [[Courier Dover]]
 | isbn = 978-0-486-61053-5
 | access-date = 2020-08-25
 | archive-date = 2022-02-04
 | archive-url = https://web.archive.org/web/20220204082418/https://books.google.com/books?id=aJZVQnqcwv4C&pg=PA221
 | url-status = live
}}</ref> In 1879, he proposed that these properties could be explained by regarding cathode rays as composed of negatively charged gaseous [[molecule]]s in a fourth state of matter in which the mean free path of the particles is so long that collisions may be ignored.<ref name=Whittaker />{{rp|394–395}}

In 1883, not yet well-known German physicist [[Heinrich Hertz]] tried to prove that cathode rays are electrically neutral and got what he interpreted as a confident absence of deflection in electrostatic, as opposed to magnetic, field. However, as [[J. J. Thomson]] explained in 1897, Hertz placed the deflecting electrodes in a highly-conductive area of the tube, resulting in a strong screening effect close to their surface.<ref name=":0" /> 

The German-born British physicist [[Arthur Schuster]] expanded upon Crookes's experiments by placing metal plates parallel to the cathode rays and applying an [[electric potential]] between the plates.<ref name="schu1890">{{Cite journal|last=Schuster|first=Arthur|date=1890|title=The discharge of electricity through gases|journal=Proceedings of the Royal Society of London|volume=47|pages=526–559|doi=10.1098/rspl.1889.0111|s2cid=96197979|doi-access=free}}</ref> The field deflected the rays toward the positively charged plate, providing further evidence that the rays carried negative charge. By measuring the amount of deflection for a given [[electric field|electric]] and [[magnetic field]], in 1890 Schuster was able to estimate the [[Mass-to-charge ratio|charge-to-mass ratio]]{{efn|Older sources list charge-to-mass rather than the modern convention of mass-to-charge ratio.}} of the ray components. However, this produced a value that was more than a thousand times greater than what was expected, so little credence was given to his calculations at the time.<ref name="leicester" /> This is because it was assumed that the charge carriers were much heavier [[hydrogen]] or [[nitrogen]] atoms.<ref name="schu1890" /> Schuster's estimates would subsequently turn out to be largely correct.

In 1892 [[Hendrik Lorentz]] suggested that the mass of these particles (electrons) could be a consequence of their electric charge.<ref>{{cite magazine |first=Frank |last=Wilczek |url=https://www.scientificamerican.com/article.cfm?id=happy-birthday-electron |title=Happy birthday, electron |magazine=Scientific American |date=June 2012 |access-date=2022-02-24 |archive-date=2013-11-01 |archive-url=https://web.archive.org/web/20131101121817/http://www.scientificamerican.com/article.cfm?id=happy-birthday-electron |url-status=live }}</ref>

[[File:J.J Thomson.jpg|thumb|upright|[[J. J. Thomson]]]]
While studying naturally [[Fluorescence|fluorescing]] minerals in 1896, the French physicist [[Henri Becquerel]] discovered that they emitted radiation without any exposure to an external energy source. These [[Radioactive decay|radioactive]] materials became the subject of much interest by scientists, including the New Zealand physicist [[Ernest Rutherford]] who discovered they emitted particles. He designated these particles [[alpha particle|alpha]] and [[beta particle|beta]], on the basis of their ability to penetrate matter.<ref>
{{cite journal
 | last = Trenn | first = T.J.
 | year = 1976
 | title = Rutherford on the Alpha-Beta-Gamma Classification of Radioactive Rays
 | journal = [[Isis (journal)|Isis]]
 | volume = 67 | issue = 1 | pages = 61–75
 | jstor = 231134
 | doi = 10.1086/351545
 | s2cid = 145281124
}}</ref> In 1900, Becquerel showed that the beta rays emitted by [[radium]] could be deflected by an electric field, and that their mass-to-charge ratio was the same as for cathode rays.<ref>
{{cite journal
 | last = Becquerel | first = H.
 | year = 1900
 | title = Déviation du Rayonnement du Radium dans un Champ Électrique
 | journal = [[Comptes rendus de l'Académie des sciences]]
 | volume = 130
 | pages = 809–815
 |language=fr}}
</ref> This evidence strengthened the view that electrons existed as components of atoms.<ref name="BaW9091">[[#refBaW2001|Buchwald and Warwick (2001:90–91).]]</ref><ref>
{{cite journal
 | last = Myers
 | first = W.G.
 | year = 1976
 | title = Becquerel's Discovery of Radioactivity in 1896
 | url = https://jnm.snmjournals.org/cgi/content/abstract/17/7/579
 | journal = [[Journal of Nuclear Medicine]]
 | volume = 17
 | issue = 7
 | pages = 579–582
 | pmid = 775027
 | access-date = 2022-02-24
 | archive-date = 2008-12-22
 | archive-url = https://web.archive.org/web/20081222023947/http://jnm.snmjournals.org/cgi/content/abstract/17/7/579
 | url-status = live
}}</ref>

In 1897, the British physicist [[J. J. Thomson]], with his colleagues [[John Sealy Townsend|John S. Townsend]] and [[Harold A. Wilson (physicist)|H. A. Wilson]], performed experiments indicating that cathode rays really were unique particles, rather than waves, atoms or molecules as was believed earlier.<ref name="thomson" /> By 1899 he showed that their charge-to-mass ratio, ''e''/''m'', was independent of cathode material.  He further showed that the negatively charged particles produced by radioactive materials, by heated materials and by illuminated materials were universal.<ref name="thomson" /><ref>
{{cite web
 |last         = Thomson
 |first        = J.J.
 |year         = 1906
 |title        = Nobel Lecture: Carriers of Negative Electricity
 |url          = https://nobelprize.org/nobel_prizes/physics/laureates/1906/thomson-lecture.pdf
 |publisher    = [[Nobel Foundation|The Nobel Foundation]]
 |access-date  = 2008-08-25 |df=dmy-all
 |archive-url  = https://web.archive.org/web/20081010100408/https://nobelprize.org/nobel_prizes/physics/laureates/1906/thomson-lecture.pdf
 |archive-date = 2008-10-10
 |url-status   = dead
}}</ref> Thomson measured ''m''/''e'' for cathode ray "corpuscles", and made good estimates of  the charge ''e'', leading to value for the mass ''m'', finding a value 1400 times less massive than the least massive ion known: hydrogen.<ref name=Whittaker/>{{rp|364}}<ref name="thomson" /> In the same year [[Emil Wiechert]] and [[Walter Kaufmann (physicist)|Walter Kaufmann]] also calculated the ''e''/''m'' ratio but did not take the step of interpreting their results as showing a new particle, while J. J. Thomson would subsequently in 1899 give estimates for the electron charge and mass as well: ''e''&nbsp;~&nbsp;{{val|6.8|e=-10|u=[[Statcoulomb|esu]]}} and ''m''&nbsp;~&nbsp;{{val|3|e=-26|u=g}}<ref>{{cite journal|last=[[Abraham Pais]]|date=1997|title=The discovery of the electron – 100 years of elementary particles|url=https://www.slac.stanford.edu/pubs/beamline/pdf/97i.pdf|journal=Beam Line|volume=1|pages=4–16|access-date=2021-09-04|archive-date=2021-09-14|archive-url=https://web.archive.org/web/20210914142755/https://www.slac.stanford.edu/pubs/beamline/pdf/97i.pdf|url-status=live}}</ref><ref>{{Cite journal|last=Kaufmann|first=W.|date=1897|title=Die magnetische Ablenkbarkeit der Kathodenstrahlen und ihre Abhängigkeit vom Entladungspotential|url=https://dx.doi.org/10.1002/andp.18972970709|journal=Annalen der Physik und Chemie|volume=297|issue=7|pages=544–552|doi=10.1002/andp.18972970709|bibcode=1897AnP...297..544K|issn=0003-3804|access-date=2022-02-24|archive-date=2022-02-24|archive-url=https://web.archive.org/web/20220224105619/https://onlinelibrary.wiley.com/doi/10.1002/andp.18972970709|url-status=live}}</ref>
[[File:Millikan.jpg|thumb|upright|[[Robert Andrews Millikan|Robert Millikan]]]]

The name "electron" was adopted for these particles by the scientific community, mainly due to the advocation by [[George Francis FitzGerald|G. F. FitzGerald]], [[Joseph Larmor|J. Larmor]], and [[Hendrik Lorentz|H. A. Lorentz]].<ref name=OHara1975>
{{cite journal
 | last =O'Hara
 | first =J. G.
 | title =George Johnstone Stoney, F.R.S., and the Concept of the Electron
 | journal =Notes and Records of the Royal Society of London
 | volume =29
 | issue =2
 | pages =265–276
 | publisher =Royal Society
 | date =March 1975
 | jstor =531468
 | doi =10.1098/rsnr.1975.0018
 | s2cid =145353314
}}</ref>{{rp|273}} The term was originally coined by [[George Johnstone Stoney]] in 1891 as a tentative name for the basic unit of electrical charge (which had then yet to be discovered).<ref>{{cite journal |last=Stoney |first=George Johnstone |author-link=George Johnstone Stoney |year=1891 |title=On the Cause of Double Lines and of Equidistant Satellites in the Spectra of Gases |journal=The Scientific Transactions of the Royal Dublin Society |volume=4 |pages=583–608 |url=https://digitalarchive.rds.ie/files/show/4769}}</ref><ref name="GJStoney" />

The electron's charge was more carefully measured by the American physicists [[Robert Andrews Millikan|Robert Millikan]] and [[Harvey Fletcher]] in their [[Oil drop experiment|oil-drop experiment]] of 1909, the results of which were published in 1911. This experiment used an electric field to prevent a charged droplet of oil from falling as a result of gravity. This device could measure the electric charge from as few as 1–150 ions with an error margin of less than 0.3%. Comparable experiments had been done earlier by Thomson's team,<ref name="thomson" /> using clouds of charged water droplets generated by electrolysis, and in 1911 by [[Abram Ioffe]], who independently obtained the same result as Millikan using charged microparticles of metals, then published his results in 1913.<ref>
{{cite journal
 | last1 = Kikoin | first1 = I.K.
 | last2 = Sominskiĭ | first2 = I.S.
 | year = 1961
 | title = Abram Fedorovich Ioffe (on his eightieth birthday)
 | journal = [[Uspekhi Fizicheskikh Nauk|Soviet Physics Uspekhi]]
 | volume = 3 | pages = 798–809
 | doi = 10.1070/PU1961v003n05ABEH005812
 | bibcode = 1961SvPhU...3..798K
 | issue = 5
}} Original publication in Russian: 
{{cite journal
 | last1 = Кикоин | first1 = И.К.
 | last2 = Соминский | first2 = М.С.
 | year = 1960
 | title = Академик А.Ф. Иоффе
 | journal = [[Uspekhi Fizicheskikh Nauk|Успехи Физических Наук]]
 | volume = 72 | issue = 10 | pages = 303–321
 | doi = 10.3367/UFNr.0072.196010e.0307
 | doi-access = free
}}</ref> However, oil drops were more stable than water drops because of their slower evaporation rate, and thus more suited to precise experimentation over longer periods of time.<ref>
{{cite journal
 | last = Millikan
 | first = R.A.
 | year = 1911
 | title = The Isolation of an Ion, a Precision Measurement of its Charge, and the Correction of Stokes's Law
 | journal = [[Physical Review]]
 | volume = 32
 | issue = 2
 | pages = 349–397
 | doi = 10.1103/PhysRevSeriesI.32.349
 | bibcode = 1911PhRvI..32..349M
 | url = https://authors.library.caltech.edu/6437/1/MILpr11b.pdf
 | access-date = 2019-06-21
 | archive-date = 2020-03-17
 | archive-url = https://web.archive.org/web/20200317204458/https://authors.library.caltech.edu/6437/1/MILpr11b.pdf
 | url-status = live
}}</ref>

Around the beginning of the twentieth century, it was found that under certain conditions a fast-moving charged particle caused a condensation of [[supersaturation|supersaturated]] water vapor along its path. In 1911, [[Charles Thomson Rees Wilson|Charles Wilson]] used this principle to devise his [[cloud chamber]] so he could photograph the tracks of charged particles, such as fast-moving electrons.<ref>
{{cite journal
 | last1 = Das Gupta | first1 = N.N.
 | last2 = Ghosh | first2 = S.K.
 | year = 1999
 | title = A Report on the Wilson Cloud Chamber and Its Applications in Physics
 | journal = [[Reviews of Modern Physics]]
 | volume = 18 | pages = 225–290
 | doi = 10.1103/RevModPhys.18.225
 | bibcode=1946RvMP...18..225G
 | issue = 2
}}</ref>

=== Atomic theory ===
[[File:Bohr atom model English.svg|right|thumb|alt=Three concentric circles about a nucleus, with an electron moving from the second to the first circle and releasing a photon|The [[Bohr model|Bohr model of the atom]], showing states of an electron with energy [[Quantum number|quantized]] by the number ''n''. An electron dropping to a lower orbit emits a photon equal to the energy difference between the orbits]]
By 1914, experiments by physicists [[Ernest Rutherford]], [[Henry Moseley]], [[James Franck]] and [[Gustav Ludwig Hertz|Gustav Hertz]] had largely established the structure of an atom as a dense [[Atomic nucleus|nucleus]] of positive charge surrounded by lower-mass electrons.<ref name="smirnov" /> In 1913, Danish physicist [[Niels Bohr]] postulated that electrons resided in quantized energy states, with their energies determined by the angular momentum of the electron's orbit about the nucleus. The electrons could move between those states, or orbits, by the emission or absorption of photons of specific frequencies. By means of these quantized orbits, he accurately explained the [[spectral line]]s of the hydrogen atom.<ref>
{{cite web
 | last = Bohr
 | first = N.
 | year = 1922
 | title = Nobel Lecture: The Structure of the Atom
 | url = https://nobelprize.org/nobel_prizes/physics/laureates/1922/bohr-lecture.pdf
 | publisher = [[Nobel Foundation|The Nobel Foundation]]
 | access-date = 2008-12-03
 | df = dmy-all
 | archive-date = 2008-12-03
 | archive-url = https://web.archive.org/web/20081203124237/http://nobelprize.org/nobel_prizes/physics/laureates/1922/bohr-lecture.pdf
 | url-status = live
}}</ref> However, Bohr's model failed to account for the relative intensities of the spectral lines and it was unsuccessful in explaining the spectra of more complex atoms.<ref name="smirnov">
{{cite book
 | last = Smirnov
 | first = B.M.
 | year = 2003
 | title = Physics of Atoms and Ions
 | url = https://books.google.com/books?id=I1O8WYOcUscC&pg=PA14
 | pages = 14–21
 | publisher = [[Springer Science+Business Media|Springer]]
 | isbn = 978-0-387-95550-6
 | access-date = 2020-08-25
 | archive-date = 2020-05-09
 | archive-url = https://web.archive.org/web/20200509044538/https://books.google.com/books?id=I1O8WYOcUscC&pg=PA14
 | url-status = live
}}</ref>

Chemical bonds between atoms were explained by [[Gilbert N. Lewis|Gilbert Newton Lewis]], who in 1916 proposed that a [[covalent bond]] between two atoms is maintained by a pair of electrons shared between them.<ref>
{{cite journal
 | last = Lewis
 | first = G.N.
 | year = 1916
 | title = The Atom and the Molecule
 | journal = [[Journal of the American Chemical Society]]
 | volume = 38
 | issue = 4
 | pages = 762–786
 | doi = 10.1021/ja02261a002
 | s2cid = 95865413
 | url = https://zenodo.org/record/1429068
 | access-date = 2019-08-25
 | archive-date = 2019-08-25
 | archive-url = https://web.archive.org/web/20190825132554/https://zenodo.org/record/1429068/files/article.pdf
 | url-status = live
}}</ref> Later, in 1927, [[Walter Heitler]] and [[Fritz London]] gave the full explanation of the electron-pair formation and chemical bonding in terms of [[quantum mechanics]].<ref name=Arabatzis>
{{cite journal
 | last1 = Arabatzis | first1 = T.
 | last2 = Gavroglu | first2 = K.
 | year = 1997
 | title = The chemists' electron
 | journal = [[European Journal of Physics]]
 | volume = 18 | pages = 150–163
 | doi = 10.1088/0143-0807/18/3/005
 | bibcode = 1997EJPh...18..150A
 | issue = 3 | s2cid = 56117976
 | url = https://pdfs.semanticscholar.org/3804/783ac9fc011aeae884a3d370a474cbfdd46f.pdf
 | archive-url = https://web.archive.org/web/20200605041731/https://pdfs.semanticscholar.org/3804/783ac9fc011aeae884a3d370a474cbfdd46f.pdf
 | url-status = dead
 | archive-date = 2020-06-05
}}</ref> In 1919, the American chemist [[Irving Langmuir]] elaborated on the Lewis's static model of the atom and suggested that all electrons were distributed in successive "concentric (nearly) spherical shells, all of equal thickness".<ref>
{{cite journal
 | last = Langmuir
 | first = I.
 | year = 1919
 | title = The Arrangement of Electrons in Atoms and Molecules
 | journal = [[Journal of the American Chemical Society]]
 | volume = 41
 | issue = 6
 | pages = 868–934
 | doi = 10.1021/ja02227a002
 | url = https://zenodo.org/record/1429026
 | access-date = 2019-06-21
 | archive-date = 2021-01-26
 | archive-url = https://web.archive.org/web/20210126003324/https://zenodo.org/record/1429026
 | url-status = live
}}</ref> In turn, he divided the shells into a number of cells each of which contained one pair of electrons. With this model Langmuir was able to qualitatively explain the [[chemical property|chemical properties]] of all elements in the periodic table,<ref name=Arabatzis /> which were known to largely repeat themselves according to the [[Periodic table|periodic law]].<ref>
{{cite book
 | last = Scerri | first = E.R.
 | year = 2007
 | title = The Periodic Table
 | url = https://archive.org/details/periodictableits0000scer/page/205
 | url-access = registration | pages=205–226
 | publisher = Oxford University Press
 | isbn = 978-0-19-530573-9
}}</ref>

In 1924, Austrian physicist [[Wolfgang Pauli]] observed that the shell-like structure of the atom could be explained by a set of four parameters that defined every quantum energy state, as long as each state was occupied by no more than a single electron. This prohibition against more than one electron occupying the same quantum energy state became known as the [[Pauli exclusion principle]].<ref>
{{cite book
 | last = Massimi
 | first = M.
 | year = 2005
 | title = Pauli's Exclusion Principle, The Origin and Validation of a Scientific Principle
 | url = https://books.google.com/books?id=YS91Gsbd13cC&pg=PA7
 | pages = 7–8
 | publisher = Cambridge University Press
 | isbn = 978-0-521-83911-2
 | access-date = 2020-08-25
 | archive-date = 2022-02-04
 | archive-url = https://web.archive.org/web/20220204071142/https://books.google.com/books?id=YS91Gsbd13cC&pg=PA7
 | url-status = live
}}</ref> The physical mechanism to explain the fourth parameter, which had two distinct possible values, was provided by the Dutch physicists [[Samuel Goudsmit]] and [[George Uhlenbeck]].  In 1925, they suggested that an electron, in addition to the angular momentum of its orbit, possesses an intrinsic angular momentum and [[magnetic moment|magnetic dipole moment]].<ref name="smirnov" /><ref>
{{cite journal
 | last1 = Uhlenbeck | first1 = G.E.
 | last2 = Goudsmith | first2 = S.
 | year = 1925
 | title = Ersetzung der Hypothese vom unmechanischen Zwang durch eine Forderung bezüglich des inneren Verhaltens jedes einzelnen Elektrons
 | journal = [[Naturwissenschaften|Die Naturwissenschaften]]
 | volume = 13 | issue = 47
 | bibcode = 1925NW.....13..953E
 |doi = 10.1007/BF01558878
 | pages = 953–954 | s2cid = 32211960
 |language=de
}}</ref> This is analogous to the rotation of the Earth on its axis as it orbits the Sun. The intrinsic angular momentum became known as [[Spin (physics)|spin]], and explained the previously mysterious splitting of spectral lines observed with a high-resolution [[Spectrometer|spectrograph]]; this phenomenon is known as [[fine structure]] splitting.<ref>
{{cite journal
 | last = Pauli | first = W.
 | year = 1923
 | title = Über die Gesetzmäßigkeiten des anomalen Zeemaneffektes
 | journal = [[European Physical Journal|Zeitschrift für Physik]]
 | volume = 16 | issue = 1 | pages = 155–164
 | bibcode = 1923ZPhy...16..155P
 | doi = 10.1007/BF01327386
 | s2cid = 122256737
 |language=de
}}</ref>

=== Quantum mechanics ===
{{See also|History of quantum mechanics}}
{{further|#Quantum properties}}
In his 1924 dissertation ''{{lang|fr|Recherches sur la théorie des quanta}}'' (Research on Quantum Theory), French physicist [[Louis de Broglie]] hypothesized that all matter can be represented as a [[Matter wave|de Broglie wave]] in the manner of [[light]].<ref name="de_broglie">
{{cite web
 | last = de Broglie
 | first = L.
 | year = 1929
 | title = Nobel Lecture: The Wave Nature of the Electron
 | url = https://nobelprize.org/nobel_prizes/physics/laureates/1929/broglie-lecture.pdf
 | publisher = [[Nobel Foundation|The Nobel Foundation]]
 | access-date = 2008-08-30
 | df = dmy-all
 | archive-date = 2008-10-04
 | archive-url = https://web.archive.org/web/20081004022001/http://nobelprize.org/nobel_prizes/physics/laureates/1929/broglie-lecture.pdf
 | url-status = live
}}</ref> That is, under the appropriate conditions, electrons and other matter would show properties of either particles or waves. The [[Corpuscular theory of light|corpuscular properties]] of a particle are demonstrated when it is shown to have a localized position in space along its trajectory at any given moment.<ref>
{{cite book
 | last = Falkenburg
 | first = B.
 | year = 2007
 | title = Particle Metaphysics: A Critical Account of Subatomic Reality
 | url = https://books.google.com/books?id=EbOz5I9RNrYC&pg=PA85
 | page = 85
 | publisher = [[Springer Science+Business Media|Springer]]
 | isbn = 978-3-540-33731-7
 | bibcode = 2007pmca.book.....F
 | access-date = 2020-08-25
 | archive-date = 2022-02-04
 | archive-url = https://web.archive.org/web/20220204082417/https://books.google.com/books?id=EbOz5I9RNrYC&pg=PA85
 | url-status = live
}}</ref> The wave-like nature of light is displayed, for example, when a beam of light is passed through parallel slits thereby creating [[Interference (wave propagation)|interference]] patterns. In 1927, [[George Paget Thomson]] and Alexander Reid discovered the interference effect was produced when a beam of electrons was passed through thin celluloid foils and later metal films, and by American physicists [[Clinton Davisson]] and [[Lester Germer]] by the reflection of electrons from a crystal of [[nickel]].<ref>
{{cite web
 | last = Davisson
 | first = C.
 | year = 1937
 | title = Nobel Lecture: The Discovery of Electron Waves
 | url = https://nobelprize.org/nobel_prizes/physics/laureates/1937/davisson-lecture.pdf
 | publisher = [[Nobel Foundation|The Nobel Foundation]]
 | access-date = 2008-08-30
 | df = dmy-all
 | archive-date = 2008-07-09
 | archive-url = https://web.archive.org/web/20080709090839/http://nobelprize.org/nobel_prizes/physics/laureates/1937/davisson-lecture.pdf
 | url-status = live
}}</ref> Alexander Reid, who was Thomson's graduate student, performed the first experiments but he died soon after in a motorcycle accident<ref>{{Cite journal |last=Navarro |first=Jaume |date=2010 |title=Electron diffraction chez Thomson: early responses to quantum physics in Britain |url=https://www.cambridge.org/core/product/identifier/S0007087410000026/type/journal_article |journal=The British Journal for the History of Science |language=en |volume=43 |issue=2 |pages=245–275 |doi=10.1017/S0007087410000026 |s2cid=171025814 |issn=0007-0874}}</ref> and is rarely mentioned.

[[File:Orbital s1.png|right|thumb|alt=A spherically symmetric blue cloud that decreases in intensity from the center outward|In quantum mechanics, the behavior of an electron in an atom is described by an [[atomic orbital|orbital]], which is a probability distribution rather than an orbit. In the figure, the shading indicates the relative probability to "find" the electron, having the energy corresponding to the given [[quantum number]]s, at that point.]]
De Broglie's prediction of a wave nature for electrons led [[Erwin Schrödinger]] to postulate a wave equation for electrons moving under the influence of the nucleus in the atom. In 1926, this equation, the [[Schrödinger equation]], successfully described how electron waves propagated.<ref>
{{cite journal
 | last = Schrödinger | first = E.
 | year = 1926
 | title = Quantisierung als Eigenwertproblem
 | journal = [[Annalen der Physik]]
 | volume = 385 | issue = 13 | pages = 437–490
 | bibcode = 1926AnP...385..437S
 | doi = 10.1002/andp.19263851302
 |language=de
}}</ref> Rather than yielding a solution that determined the location of an electron over time, this wave equation also could be used to predict the probability of finding an electron near a position, especially a position near where the electron was bound in space, for which the electron wave equations did not change in time. This approach led to a second formulation of [[quantum mechanics]] (the first by Heisenberg in 1925), and solutions of Schrödinger's equation, like Heisenberg's, provided derivations of the energy states of an electron in a hydrogen atom that were equivalent to those that had been derived first by Bohr in 1913, and that were known to reproduce the hydrogen spectrum.<ref>
{{cite book
 | last = Rigden
 | first = J.S.
 | year = 2003
 | title = Hydrogen
 | url = https://books.google.com/books?id=FhFxn_lUvz0C&pg=PT66
 | publisher = Harvard University Press
 | pages = 59–86
 | isbn = 978-0-674-01252-3
 | access-date = 2020-08-25
 | archive-date = 2022-02-04
 | archive-url = https://web.archive.org/web/20220204082407/https://books.google.com/books?id=FhFxn_lUvz0C&pg=PT66
 | url-status = live
}}</ref> Once spin and the interaction between multiple electrons were describable, quantum mechanics made it possible to predict the configuration of electrons in atoms with atomic numbers greater than hydrogen.<ref>
{{cite book
 | last = Reed
 | first = B.C.
 | year = 2007
 | title = Quantum Mechanics
 | url = https://books.google.com/books?id=4sluccbpwjsC&pg=PA275
 | pages = 275–350
 | publisher = [[Jones & Bartlett Learning|Jones & Bartlett Publishers]]
 | isbn = 978-0-7637-4451-9
 | access-date = 2020-08-25
 | archive-date = 2022-02-04
 | archive-url = https://web.archive.org/web/20220204082419/https://books.google.com/books?id=4sluccbpwjsC&pg=PA275
 | url-status = live
}}</ref>

In 1928, building on Wolfgang Pauli's work, [[Paul Dirac]] produced a model of the electron&nbsp;– the [[Dirac equation]], consistent with [[Principle of relativity|relativity]] theory, by applying relativistic and symmetry considerations to the [[Hamiltonian (quantum mechanics)|hamiltonian]] formulation of the quantum mechanics of the electro-magnetic field.<ref>
{{cite journal
 |last         = Dirac
 |first        = P.A.M.
 |year         = 1928
 |title        = The Quantum Theory of the Electron
 |journal      = [[Proceedings of the Royal Society#Proceedings of the Royal Society A|Proceedings of the Royal Society A]]
 |volume       = 117
 |issue        = 778
 |pages        = 610–624
 |doi          = 10.1098/rspa.1928.0023
 |bibcode      = 1928RSPSA.117..610D
 |url          = https://rspa.royalsocietypublishing.org/content/royprsa/117/778/610.full.pdf
 |doi-access   = free
 |access-date  = 2022-02-24
 |archive-date = 2018-11-25
 |archive-url  = https://web.archive.org/web/20181125224103/http://rspa.royalsocietypublishing.org/content/royprsa/117/778/610.full.pdf
 |url-status   = live
}}</ref> In order to resolve some problems within his relativistic equation, Dirac developed in 1930 a model of the vacuum as an infinite sea of particles with negative energy, later dubbed the [[Dirac sea]]. This led him to predict the existence of a positron, the [[antimatter]] counterpart of the electron.<ref>
{{cite web
 | last = Dirac
 | first = P.A.M.
 | year = 1933
 | title = Nobel Lecture: Theory of Electrons and Positrons
 | url = https://nobelprize.org/nobel_prizes/physics/laureates/1933/dirac-lecture.pdf
 | publisher = [[Nobel Foundation|The Nobel Foundation]]
 | access-date = 2008-11-01
 | df = dmy-all
 | archive-date = 2008-07-23
 | archive-url = https://web.archive.org/web/20080723220816/http://nobelprize.org/nobel_prizes/physics/laureates/1933/dirac-lecture.pdf
 | url-status = live
}}</ref> This particle was discovered in 1932 by [[Carl David Anderson|Carl Anderson]], who proposed calling standard electrons ''negatrons'' and using ''electron'' as a generic term to describe both the positively and negatively charged variants.<ref>{{Cite journal |last=Anderson |first=Carl D. |date=1933-03-15 |title=The Positive Electron |journal=Physical Review |language=en |volume=43 |issue=6 |pages=491–494 |doi=10.1103/PhysRev.43.491 |bibcode=1933PhRv...43..491A |issn=0031-899X|doi-access=free }}</ref>

In 1947, [[Willis Lamb]], working in collaboration with graduate student [[Robert Retherford]], found that certain quantum states of the hydrogen atom, which should have the same energy, were shifted in relation to each other; the difference came to be called the [[Lamb shift]]. About the same time, [[Polykarp Kusch]], working with [[Henry M. Foley]], discovered the magnetic moment of the electron is slightly larger than predicted by Dirac's theory. This small difference was later called [[anomalous magnetic dipole moment]] of the electron. This difference was later explained by the theory of [[quantum electrodynamics]], developed by [[Sin-Itiro Tomonaga]], [[Julian Schwinger]] and
[[Richard Feynman]] in the late 1940s.<ref>
{{cite web
 | title = The Nobel Prize in Physics 1965
 | url = https://nobelprize.org/nobel_prizes/physics/laureates/1965/
 | publisher = [[Nobel Foundation|The Nobel Foundation]]
 | access-date = 2008-11-04
 | df = dmy-all
 | archive-date = 2008-10-24
 | archive-url = https://web.archive.org/web/20081024052537/http://nobelprize.org/nobel_prizes/physics/laureates/1965/
 | url-status = live
}}</ref>

=== Particle accelerators ===
With the development of the [[particle accelerator]] during the first half of the twentieth century, physicists began to delve deeper into the properties of [[subatomic particle]]s.<ref>
{{cite journal
 | last = Panofsky
 | first = W.K.H.
 | year = 1997
 | title = The Evolution of Particle Accelerators & Colliders
 | url = https://www.slac.stanford.edu/pubs/beamline/27/1/27-1-panofsky.pdf
 | journal = Beam Line
 | volume = 27
 | issue = 1
 | pages = 36–44
 | access-date = 2008-09-15
 | df = dmy-all
 | archive-date = 2008-09-09
 | archive-url = https://web.archive.org/web/20080909234139/http://www.slac.stanford.edu/pubs/beamline/27/1/27-1-panofsky.pdf
 | url-status = live
}}</ref> The first successful attempt to accelerate electrons using [[electromagnetic induction]] was made in 1942 by [[Donald William Kerst|Donald Kerst]]. His initial [[betatron]] reached energies of 2.3&nbsp;MeV, while subsequent betatrons achieved 300&nbsp;MeV. In 1947, [[synchrotron radiation]] was discovered with a 70&nbsp;MeV electron synchrotron at [[General Electric]]. This radiation was caused by the acceleration of electrons through a magnetic field as they moved near the speed of light.<ref>
{{cite journal
 | last = Elder | first = F.R.
 | year = 1947
 | title = Radiation from Electrons in a Synchrotron
 | journal = [[Physical Review]]
 | volume = 71 | issue = 11 | pages = 829–830
 | doi = 10.1103/PhysRev.71.829.5
 |bibcode = 1947PhRv...71..829E |display-authors=etal
}}</ref>

With a beam energy of 1.5&nbsp;GeV, the first high-energy
particle [[collider]] was [[ADONE]], which began operations in 1968.<ref>
{{cite book
 | last = Hoddeson
 | first = L.
 | year = 1997
 | title = The Rise of the Standard Model: Particle Physics in the 1960s and 1970s
 | url = https://books.google.com/books?id=klLUs2XUmOkC&pg=PA25
 | pages = 25–26
 | publisher = [[Cambridge University Press]]
 | isbn = 978-0-521-57816-5
 | display-authors = etal
 | access-date = 2020-08-25
 | archive-date = 2022-02-04
 | archive-url = https://web.archive.org/web/20220204082414/https://books.google.com/books?id=klLUs2XUmOkC&pg=PA25
 | url-status = live
}}</ref> This device accelerated electrons and positrons in opposite directions, effectively doubling the energy of their collision when compared to striking a static target with an electron.<ref>
{{cite journal
 | last = Bernardini | first = C.
 | year = 2004
 | title = AdA: The First Electron–Positron Collider
 | journal = [[Physics in Perspective]]
 | volume = 6 | issue = 2 | pages = 156–183
 | bibcode = 2004PhP.....6..156B
 | doi = 10.1007/s00016-003-0202-y
 | s2cid = 122534669
}}</ref> The [[Large Electron–Positron Collider]] (LEP) at [[CERN]], which was operational from 1989 to 2000, achieved collision energies of 209&nbsp;GeV and made important measurements for the [[Standard Model]] of particle physics.<ref>
{{cite web
 | year = 2008
 | title = Testing the Standard Model: The LEP experiments
 | url = https://public.web.cern.ch/PUBLIC/en/Research/LEPExp-en.html
 | publisher = [[CERN]]
 | access-date = 2008-09-15
 | df = dmy-all
 | archive-date = 2008-09-14
 | archive-url = https://web.archive.org/web/20080914164129/http://public.web.cern.ch/public/en/Research/LEPExp-en.html
 | url-status = live
}}</ref><ref>
{{cite journal
 | year = 2000
 | title = LEP reaps a final harvest
 | url = https://cerncourier.com/cws/article/cern/28335
 | journal = [[CERN Courier]]
 | volume = 40
 | issue = 10
 | access-date = 2022-02-24
 | archive-date = 2017-09-30
 | archive-url = https://web.archive.org/web/20170930222305/http://cerncourier.com/cws/article/cern/28335
 | url-status = live
}}</ref>

=== Confinement of individual electrons ===
Individual electrons can now be easily confined in ultra small ({{nowrap|1=''L'' = 20 nm}}, {{nowrap|1=''W'' = 20 nm}}) CMOS transistors operated at cryogenic temperature over a range of −269&nbsp;°C (4&nbsp;[[kelvin|K]]) to about −258&nbsp;°C (15&nbsp;[[kelvin|K]]).<ref>
{{cite journal
 | last1 = Prati | first1 = E.
 | last2 = De Michielis | first2 = M.
 | last3 = Belli | first3 = M.
 | last4 = Cocco | first4 = S.
 | last5 = Fanciulli | first5 = M.
 | last6 = Kotekar-Patil | first6 = D.
 | last7 = Ruoff | first7 = M.
 | last8 = Kern | first8 = D.P.
 | last9 = Wharam | first9 = D.A.
 | last10 = Verduijn | first10 = J.
 | last11 = Tettamanzi | first11 = G.C.
 | last12 = Rogge | first12 = S.
 | last13 = Roche | first13 = B.
 | last14 = Wacquez | first14 = R.
 | last15 = Jehl | first15 = X.
 | last16 = Vinet | first16 = M.
 | last17 = Sanquer | first17 = M.
 | title = Few electron limit of n-type metal oxide semiconductor single electron transistors
 | journal = Nanotechnology
 | volume = 23 | issue = 21 | pages = 215204
 | year = 2012
 | doi = 10.1088/0957-4484/23/21/215204
 | pmid =  22552118 |arxiv = 1203.4811
 | bibcode = 2012Nanot..23u5204P | citeseerx = 10.1.1.756.4383 | s2cid = 206063658
}}</ref> The electron wavefunction spreads in a semiconductor lattice and negligibly interacts with the valence band electrons, so it can be treated in the single particle formalism, by replacing its mass with the [[Effective mass (solid-state physics)|effective mass tensor]].

== Characteristics ==

=== Classification ===
[[File:Standard Model of Elementary Particles.svg|right|thumb|upright=1.25|alt=A table with four rows and four columns, with each cell containing a particle identifier|Standard Model of elementary particles. The electron (symbol e) is on the left.]]
In the [[Standard Model]] of particle physics, electrons belong to the group of subatomic particles called [[lepton]]s, which are believed to be fundamental or [[elementary particle]]s. Electrons have the lowest mass of any charged lepton (or electrically charged particle of any type) and belong to the first-[[generation (particle physics)|generation]] of fundamental particles.<ref>
{{cite journal
 | last1 = Frampton | first1 = P.H.
 | last2 = Hung | first2 = P.Q.
 | last3 = Sher | first3 = Marc
 | year = 2000
 | title = Quarks and Leptons Beyond the Third Generation
 | journal = [[Physics Reports]]
 | volume = 330 | issue = 5–6 | pages = 263–348
 | doi = 10.1016/S0370-1573(99)00095-2
 |arxiv = hep-ph/9903387 |bibcode = 2000PhR...330..263F
 | s2cid = 119481188
}}</ref> The second and third generation contain charged leptons, the [[muon]] and the [[tau (particle)|tau]], which are identical to the electron in charge, [[Spin (physics)|spin]] and [[fundamental interaction|interactions]], but are more massive. Leptons differ from the other basic constituent of matter, the [[quark]]s, by their lack of [[strong interaction]]. All members of the lepton group are fermions because they all have half-odd integer spin; the electron has spin {{sfrac|1|2}}.<ref name="raith">
{{cite book
 | last1 = Raith | first1 = W.
 | last2 = Mulvey | first2 = T.
 | year = 2001
 | title = Constituents of Matter: Atoms, Molecules, Nuclei and Particles
 | pages = 777–781
 | publisher = [[CRC Press]]
 | isbn = 978-0-8493-1202-1
}}</ref>

=== Fundamental properties ===
The [[invariant mass]] of an electron is approximately [[Orders of magnitude (mass)#The least massive things: below 10−24 kg|{{val|9.109|e=-31|u=kg}}]],<ref name="CODATA" /> or {{val|5.489|e=-4|ul=Da}}. Due to [[mass–energy equivalence]], this corresponds to a rest energy of [[Orders of magnitude (energy)#Electron energy|{{convert|0.511|MeV|J|abbr=on}}]]. The ratio between the mass of a [[proton]] and that of an electron is about 1836.<ref name=nist_codata_mu>
{{cite web
 | title = CODATA value: proton-electron mass ratio
 | url = https://physics.nist.gov/cgi-bin/cuu/Value?mpsme
 | work = 2006 CODATA recommended values
 | publisher = [[National Institute of Standards and Technology]]
 | access-date = 2009-07-18
 | df = dmy-all
 | archive-date = 2019-03-28
 | archive-url = https://web.archive.org/web/20190328001314/https://physics.nist.gov/cgi-bin/cuu/Value?mpsme
 | url-status = live
}}</ref><ref name=Zombeck2007>
{{cite book
 | last = Zombeck
 | first = M.V.
 | year = 2007
 | title = Handbook of Space Astronomy and Astrophysics
 | url = https://books.google.com/books?id=tp_G85jm6IAC&pg=PA14
 | edition = 3rd
 | page = 14
 | publisher = Cambridge University Press
 | isbn = 978-0-521-78242-5
 | access-date = 2020-08-25
 | archive-date = 2022-02-04
 | archive-url = https://web.archive.org/web/20220204082414/https://books.google.com/books?id=tp_G85jm6IAC&pg=PA14
 | url-status = live
}}</ref> Astronomical measurements show that the [[proton-to-electron mass ratio]] has held the same value, as is predicted by the Standard Model, for at least half the [[age of the universe]].<ref>
{{cite journal
 | last = Murphy | first = M.T.
 | year = 2008
 | title = Strong Limit on a Variable Proton-to-Electron Mass Ratio from Molecules in the Distant Universe
 | journal = [[Science (journal)|Science]]
 | volume = 320 | issue = 5883 | pages = 1611–1613
 | doi = 10.1126/science.1156352
 | pmid = 18566280
 |bibcode = 2008Sci...320.1611M |arxiv = 0806.3081 | s2cid = 2384708
 |display-authors=etal
}}</ref>

Electrons have an [[electric charge]] of {{val|-1.602176634|e=-19}} [[coulomb]]s,<ref name="CODATA">The original source for CODATA is 
{{cite journal
 | last1 = Mohr | first1 = P.J.
 | last2 = Taylor | first2 = B.N.
 | last3 = Newell | first3 = D.B.
 | year = 2008
 | title = CODATA recommended values of the fundamental physical constants
 | journal = [[Reviews of Modern Physics]]
 | volume = 80 | pages = 633–730
 | doi = 10.1103/RevModPhys.80.633 | bibcode=2008RvMP...80..633M
 | issue = 2
 |arxiv = 0801.0028 | citeseerx = 10.1.1.150.1225
}}
: Individual physical constants from the CODATA are available at: 
{{cite web
 | url = https://physics.nist.gov/cuu/
 | title = The NIST Reference on Constants, Units and Uncertainty
 | publisher = [[National Institute of Standards and Technology]]
 | access-date = 2009-01-15
 | archive-date = 2009-01-16
 | archive-url = https://web.archive.org/web/20090116162522/http://physics.nist.gov/cuu/
 | url-status = live
}}</ref> which is used as a standard unit of charge for subatomic particles, and is also called the [[elementary charge]]. Within the limits of experimental accuracy, the electron charge is identical to the charge of a proton, but with the opposite sign.<ref>
{{cite journal
 | last1 = Zorn | first1 = J.C.
 | last2 = Chamberlain | first2 = G.E.
 | last3 = Hughes | first3 = V.W.
 | year = 1963
 | title = Experimental Limits for the Electron–Proton Charge Difference and for the Charge of the Neutron
 | journal = [[Physical Review]]
 | volume = 129 | issue = 6 | pages = 2566–2576
 | doi = 10.1103/PhysRev.129.2566
 |bibcode = 1963PhRv..129.2566Z
}}</ref> The electron is commonly symbolized by {{subatomicParticle|electron}}, and the positron is symbolized by {{subatomicParticle|positron}}.<ref name="raith" /><ref name="CODATA" />

The electron has an intrinsic [[angular momentum]] or spin of {{sfrac|''ħ''|2}}.<ref name="CODATA" /> This property is usually stated by referring to the electron as a [[spin-1/2]] particle.<ref name="raith" /> For such particles the spin magnitude is {{sfrac|''ħ''|2}},<ref name=Gupta2001 /> while the result of the measurement of a [[Projection (mathematics)|projection]] of the spin on any axis can only be ±{{sfrac|''ħ''|2}}. In addition to spin, the electron has an intrinsic [[Electron magnetic moment|magnetic moment]] along its spin axis.<ref name="CODATA" /> It is approximately equal to one [[Bohr magneton]],<ref name=Hanneke />{{efn|Bohr magneton:
: <math>\textstyle\mu_{\mathrm{B}}=\frac{e\hbar}{2m_{\mathrm{e}}}</math>}} which is a physical constant that is equal to {{physconst|muB|after=.}} The orientation of the spin with respect to the momentum of the electron defines the property of elementary particles known as [[helicity (particle physics)|helicity]].<ref name="anastopoulos">
{{cite book
 | last = Anastopoulos
 | first = C.
 | year = 2008
 | title = Particle Or Wave: The Evolution of the Concept of Matter in Modern Physics
 | url = https://books.google.com/books?id=rDEvQZhpltEC&pg=PA261
 | publisher = Princeton University Press
 | pages = 261–262
 | isbn = 978-0-691-13512-0
 | access-date = 2020-08-25
 | archive-date = 2021-01-07
 | archive-url = https://web.archive.org/web/20210107160318/https://books.google.com/books?id=rDEvQZhpltEC&pg=PA261
 | url-status = live
}}</ref>

The electron has no known [[preon|substructure]].<ref name="prl50">
{{cite journal
 | last1 = Eichten | first1 = E.J.
 | last2 = Peskin | first2 = M.E.
 | last3 = Peskin | first3 = M.
 | year = 1983
 | title = New Tests for Quark and Lepton Substructure
 | journal = [[Physical Review Letters]]
 | volume = 50 | pages = 811–814 | issue = 11
 | doi = 10.1103/PhysRevLett.50.811 | bibcode=1983PhRvL..50..811E
 | osti = 1446807
 | s2cid = 119918703
}}</ref><ref>
{{cite journal
 | last = Gabrielse | first = G.
 | year = 2006
 | title = New Determination of the Fine Structure Constant from the Electron ''g'' Value and QED
 | journal = [[Physical Review Letters]]
 | volume = 97 | pages = 030802(1–4)
 | doi = 10.1103/PhysRevLett.97.030802
 | pmid = 16907491
 | bibcode=2006PhRvL..97c0802G
 | issue = 3
 | s2cid = 763602
 |display-authors=etal
}}</ref> Nevertheless, in [[condensed matter physics]], [[spin–charge separation]] can occur in some materials. In such cases, electrons 'split' into three independent particles, the [[spinon]], the [[orbiton]] and the [[Holon (physics)|holon]] (or chargon). The electron can always be theoretically considered as a bound state of the three, with the spinon carrying the spin of the electron, the orbiton carrying the orbital degree of freedom and the chargon carrying the charge, but in certain conditions they can behave as independent [[quasiparticles]].<ref name=bbc>{{cite web |url=https://news.bbc.co.uk/1/hi/england/8227861.stm |title=UK {{pipe}} England {{pipe}} Physicists 'make electrons split' |work=BBC News |date=2009-08-28 |access-date=2016-07-11 |archive-date=2017-08-31 |archive-url=https://web.archive.org/web/20170831102806/http://news.bbc.co.uk/1/hi/england/8227861.stm |url-status=live }}</ref><ref>[https://www.sciencedaily.com/releases/2009/07/090730141607.htm Discovery About Behavior Of Building Block Of Nature Could Lead To Computer Revolution] {{Webarchive|url=https://web.archive.org/web/20190404130054/https://www.sciencedaily.com/releases/2009/07/090730141607.htm |date=2019-04-04 }}. ''Science Daily'' (July 31, 2009)</ref><ref name=gov>{{cite web |last=Yarris |first=Lynn |url=https://www.lbl.gov/Science-Articles/Archive/ALS-spinons-holons.html |title=First Direct Observations of Spinons and Holons |publisher=Lbl.gov |date=2006-07-13 |access-date=2016-07-11 |archive-date=2022-02-24 |archive-url=https://web.archive.org/web/20220224105553/https://www2.lbl.gov/Science-Articles/Archive/ALS-spinons-holons.html |url-status=live }}</ref>

The issue of the radius of the electron is a challenging problem of modern theoretical physics. The admission of the hypothesis of a finite radius of the electron is incompatible to the premises of the theory of relativity. On the other hand, a point-like electron (zero radius) generates serious mathematical difficulties due to the [[self-energy]] of the electron tending to infinity.<ref>[[Eduard Shpolsky]], Atomic physics (Atomnaia fizika), second edition, 1951</ref> Observation of a single electron in a [[Penning trap]] suggests the upper limit of the particle's radius to be 10<sup>−22</sup>&nbsp;meters.<ref>
{{cite journal
 | last = Dehmelt | first = H.
 | year = 1988
 | title = A Single Atomic Particle Forever Floating at Rest in Free Space: New Value for Electron Radius
 | journal = [[Physica Scripta]]
 | volume = T22 | pages = 102–110
 | doi = 10.1088/0031-8949/1988/T22/016
 |bibcode = 1988PhST...22..102D | s2cid = 250760629
}}</ref>
The upper bound of the electron radius of 10<sup>−18</sup>&nbsp;meters<ref>{{cite web |author-link=Gerald Gabrielse |first=Gerald |last=Gabrielse |url=https://gabrielse.physics.harvard.edu/gabrielse/overviews/ElectronSubstructure/ElectronSubstructure.html |title=Electron Substructure |department=Physics |publisher=Harvard University |access-date=2016-06-21 |archive-date=2019-04-10 |archive-url=https://web.archive.org/web/20190410164332/https://gabrielse.physics.harvard.edu/gabrielse/overviews/ElectronSubstructure/ElectronSubstructure.html |url-status=dead }}</ref> can be derived using the [[uncertainty relation]] in energy. There ''is'' also a physical constant called the "[[classical electron radius]]", with the much larger value of {{val|2.8179|e=-15|u=m}}, greater than the radius of the proton. However, the terminology comes from a simplistic calculation that ignores the effects of [[quantum mechanics]]; in reality, the so-called classical electron radius has little to do with the true fundamental structure of the electron.<ref>
{{cite book
 | last = Meschede
 | first = D.
 | year = 2004
 | title = Optics, light and lasers: The Practical Approach to Modern Aspects of Photonics and Laser Physics
 | url = https://books.google.com/books?id=PLISLfBLcmgC&pg=PA168
 | publisher = [[Wiley-VCH]]
 | page = 168
 | isbn = 978-3-527-40364-6
 | access-date = 2020-08-25
 | archive-date = 2014-08-21
 | archive-url = https://web.archive.org/web/20140821185221/http://books.google.com/books?id=PLISLfBLcmgC&pg=PA168
 | url-status = live
}}</ref><ref name=HakenWolfBrewer2005 /><ref group="lower-alpha">The classical electron radius is derived as follows. Assume that the electron's charge is spread uniformly throughout a spherical volume. Since one part of the sphere would repel the other parts, the sphere contains electrostatic potential energy. This energy is assumed to equal the electron's [[Invariant mass#Rest energy|rest energy]], defined by [[special relativity]] (''E''&nbsp;=&nbsp;''mc''<sup>2</sup>).<br />
From [[electrostatics]] theory, the [[potential energy]] of a sphere with radius ''r'' and charge ''e'' is given by:
: <math>E_{\mathrm p} = \frac{e^2}{8\pi \varepsilon_0 r},</math>
where ''ε''<sub>0</sub> is the [[vacuum permittivity]]. For an electron with rest mass ''m''<sub>0</sub>, the rest energy is equal to:
: <math>\textstyle E_{\mathrm p} = m_0 c^2,</math>
where ''c'' is the speed of light in vacuum. Setting them equal and solving for ''r'' gives the classical electron radius.<br />
See: Haken, Wolf, & Brewer (2005).</ref>

There are [[elementary particle]]s that spontaneously [[Particle decay|decay]] into less massive particles. An example is the [[muon]], with a [[Exponential decay#Mean lifetime|mean lifetime]] of {{val|2.2|e=-6}}&nbsp;seconds, which decays into an electron, a muon [[neutrino]] and an electron [[neutrino#Antineutrinos|antineutrino]]. The electron, on the other hand, is thought to be stable on theoretical grounds: the electron is the least massive particle with non-zero electric charge, so its decay would violate [[charge conservation]].<ref>
{{cite journal
 | last = Steinberg | first = R.I.
 | year = 1999
 | title = Experimental test of charge conservation and the stability of the electron
 | journal = [[Physical Review D]]
 | volume = 61 | issue = 2 | pages = 2582–2586
 | doi = 10.1103/PhysRevD.12.2582
 |bibcode = 1975PhRvD..12.2582S |display-authors=etal
}}</ref> The experimental lower bound for the electron's mean lifetime is {{val|6.6|e=28}} years, at a 90% [[confidence interval|confidence level]].<ref name=bx2015 /><ref>
{{cite journal
 |last            = Beringer |first=J.
 |display-authors = etal
 |collaboration   = Particle Data Group
 |year            = 2012
 |title           = Review of Particle Physics: [electron properties]
 |journal         = [[Physical Review D]]
 |volume          = 86
 |issue           = 1
 |pages           = 010001
 |doi             = 10.1103/PhysRevD.86.010001
 |bibcode         = 2012PhRvD..86a0001B
 |url             = https://pdg.lbl.gov/2012/listings/rpp2012-list-electron.pdf
 |doi-access      = free
 |access-date     = 2022-02-24
 |archive-date    = 2022-01-15
 |archive-url     = https://web.archive.org/web/20220115063155/https://pdg.lbl.gov/2012/listings/rpp2012-list-electron.pdf
 |url-status      = live
}}</ref><ref>
{{cite journal
 | last1 =  Back | first1 = H.O. |display-authors=etal
 | year = 2002
 | title = Search for electron decay mode e → γ + ν with prototype of Borexino detector
 | journal = [[Physics Letters B]]
 | volume = 525 | issue = 1–2 | pages = 29–40
 | doi = 10.1016/S0370-2693(01)01440-X | doi-access = free
 | bibcode = 2002PhLB..525...29B
}}</ref>

=== Quantum properties ===
As with all particles, electrons can act as waves. This is called the [[wave–particle duality]] and can be demonstrated using the [[double-slit experiment]].

The wave-like nature of the electron allows it to pass through two parallel slits simultaneously, rather than just one slit as would be the case for a classical particle. In quantum mechanics, the wave-like property of one particle can be described mathematically as a [[complex number|complex]]-valued function, the [[wave function]], commonly denoted by the [[Greek alphabet|Greek letter]] [[Psi (Greek)|psi]] (''ψ''). When the [[Absolute value#Complex numbers|absolute value]] of this function is [[square (algebra)|squared]], it gives the probability that a particle will be observed near a location—a [[probability density function|probability density]].<ref name="munowitz">
{{cite book
 | last = Munowitz | first = M.
 | year = 2005
 | title = Knowing the Nature of Physical Law
 | url = https://archive.org/details/knowingnatureofp0000muno
 | url-access = registration | page = [https://archive.org/details/knowingnatureofp0000muno/page/162 162] | publisher = Oxford University Press
 | isbn = 978-0-19-516737-5
}}</ref>{{rp|162–218}}

[[File:Asymmetricwave2.png|right|thumb|alt=A three dimensional projection of a two dimensional plot. There are symmetric hills along one axis and symmetric valleys along the other, roughly giving a saddle-shape|Example of an antisymmetric wave function for a quantum state of [[Particle in a box|two identical fermions in a one-dimensional box]], with each horizontal axis corresponding to the position of one particle. If the particles swap position, the wave function inverts its sign.]]
Electrons are [[identical particles]] because they cannot be distinguished from each other by their intrinsic physical properties. In quantum mechanics, this means that a pair of interacting electrons must be able to swap positions without an observable change to the state of the system. The wave function of fermions, including electrons, is antisymmetric, meaning that it changes sign when two electrons are swapped; that is, {{nowrap|''ψ''(''r''<sub>1</sub>, ''r''<sub>2</sub>) {{=}} −''ψ''(''r''<sub>2</sub>, ''r''<sub>1</sub>)}}, where the variables ''r''<sub>1</sub> and ''r''<sub>2</sub> correspond to the first and second electrons, respectively. Since the absolute value is not changed by a sign swap, this corresponds to equal probabilities. [[Boson]]s, such as the photon, have symmetric wave functions instead.<ref name="munowitz" />{{rp|162–218}}

In the case of antisymmetry, solutions of the wave equation for interacting electrons result in a [[zero probability]] that each pair will occupy the same location or state. This is responsible for the [[Pauli exclusion principle]], which precludes any two electrons from occupying the same quantum state. This principle explains many of the properties of electrons. For example, it causes groups of bound electrons to occupy different [[atomic orbital|orbitals]] in an atom, rather than all overlapping each other in the same orbit.<ref name="munowitz" />{{rp|162–218}}

=== Virtual particles ===
{{Main|Virtual particle}}
In a simplified picture, which often tends to give the wrong idea but may serve to illustrate some aspects, every photon spends some time as a combination of a virtual electron plus its antiparticle, the virtual positron, which rapidly [[Annihilation|annihilate]] each other shortly thereafter.<ref>
{{cite magazine
 | last = Kane | first = G.
 | date = October 9, 2006
 | url = https://www.sciam.com/article.cfm?id=are-virtual-particles-rea&topicID=13
 | title = Are virtual particles really constantly popping in and out of existence? Or are they merely a mathematical bookkeeping device for quantum mechanics?
 | magazine = [[Scientific American]]
 | access-date = 2008-09-19 |df=dmy-all
}}</ref> The combination of the energy variation needed to create these particles, and the time during which they exist, fall under the threshold of detectability expressed by the [[Uncertainty principle|Heisenberg uncertainty relation]], Δ''E''&nbsp;·&nbsp;Δ''t''&nbsp;≥&nbsp;''ħ''. In effect, the energy needed to create these virtual particles, Δ''E'', can be "borrowed" from the [[Vacuum state|vacuum]] for a period of time, Δ''t'', so that their product is no more than the [[reduced Planck constant]], {{nowrap|''ħ'' ≈ {{val|6.6|e=-16|u=eV·s}}}}. Thus, for a virtual electron, Δ''t'' is at most {{val|1.3|e=-21|u=s}}.<ref name="taylor">
{{cite book
 | last = Taylor
 | first = J.
 | year = 1989
 | chapter = Gauge Theories in Particle Physics
 | chapter-url = https://books.google.com/books?id=akb2FpZSGnMC&pg=PA464
 | editor = Davies, Paul
 | title = The New Physics
 | page = 464
 | publisher = [[Cambridge University Press]]
 | isbn = 978-0-521-43831-5
 | access-date = 2020-08-25
 | archive-date = 2014-09-21
 | archive-url = https://web.archive.org/web/20140921171834/http://books.google.com/books?id=akb2FpZSGnMC&pg=PA464
 | url-status = live
}}</ref>

[[File:Virtual pairs near electron.png|right|thumb|alt=A sphere with a minus sign at lower left symbolizes the electron, while pairs of spheres with plus and minus signs show the virtual particles|A schematic depiction of virtual electron–positron pairs appearing at random near an electron (at lower left)]]
While an electron–positron virtual pair is in existence, the [[Coulomb's law|Coulomb force]] from the ambient [[electric field]] surrounding an electron causes a created positron to be attracted to the original electron, while a created electron experiences a repulsion. This causes what is called [[vacuum polarization]]. In effect, the vacuum behaves like a medium having a [[Relative permittivity|dielectric permittivity]] more than [[1|unity]]. Thus the effective charge of an electron is actually smaller than its true value, and the charge decreases with increasing distance from the electron.<ref name="genz">
{{cite book
 | last = Genz | first = H.
 | year = 2001
 | title = Nothingness: The Science of Empty Space
 | pages = 241–243, 245–247
 | publisher = [[Da Capo Press]]
 | isbn = 978-0-7382-0610-3
}}</ref><ref>
{{cite news
 | last = Gribbin
 | first = J.
 | date = January 25, 1997
 | title = More to electrons than meets the eye
 | magazine = [[New Scientist]]
 | url = https://www.newscientist.com/article/mg15320662.300-science--more-to-electrons-than-meets-the-eye.html
 | access-date = 2008-09-17
 | df = dmy-all
 | archive-date = 2015-02-11
 | archive-url = https://web.archive.org/web/20150211085433/http://www.newscientist.com/article/mg15320662.300-science--more-to-electrons-than-meets-the-eye.html
 | url-status = live
}}</ref> This polarization was confirmed experimentally in 1997 using the Japanese [[KEKB (accelerator)|TRISTAN]] particle accelerator.<ref>
{{cite journal
 | last1 = Levine | first1 = I. |display-authors=etal
 | year = 1997
 | title = Measurement of the Electromagnetic Coupling at Large Momentum Transfer
 | journal = [[Physical Review Letters]]
 | volume = 78 | issue = 3 | pages = 424–427
 | doi = 10.1103/PhysRevLett.78.424
 | bibcode=1997PhRvL..78..424L
}}</ref> Virtual particles cause a comparable [[shielding effect]] for the mass of the electron.<ref>
{{cite conference
 | last = Murayama | first = H.
 | date =10–17 March 2006
 | title = Supersymmetry Breaking Made Easy, Viable and Generic
 | conference = Proceedings of the XLIInd Rencontres de Moriond on Electroweak Interactions and Unified Theories
 | place = La Thuile, Italy
 | arxiv = 0709.3041
 | bibcode = 2007arXiv0709.3041M
}} – lists a 9% mass difference for an electron that is the size of the [[Planck length|Planck distance]].</ref>

The interaction with virtual particles also explains the small (about 0.1%) deviation of the intrinsic magnetic moment of the electron from the Bohr magneton (the [[Anomalous magnetic dipole moment|anomalous magnetic moment]]).<ref name=Hanneke>
{{cite journal
 | last1 = Odom | first1 = B. |display-authors=etal
 | year = 2006
 | title = New Measurement of the Electron Magnetic Moment Using a One-Electron Quantum Cyclotron
 | journal = [[Physical Review Letters]]
 | volume = 97 | issue=3 | pages = 030801
 | doi = 10.1103/PhysRevLett.97.030801
 | pmid=16907490 | bibcode=2006PhRvL..97c0801O
}}</ref><ref>
{{cite journal
 | last = Schwinger | first = J.
 | year = 1948
 | title = On Quantum-Electrodynamics and the Magnetic Moment of the Electron
 | journal = [[Physical Review]]
 | volume = 73 | issue = 4 | pages = 416–417
 | doi = 10.1103/PhysRev.73.416 | doi-access = free
 | bibcode = 1948PhRv...73..416S
}}</ref> The extraordinarily precise agreement of this predicted difference with the experimentally determined value is viewed as one of the great achievements of [[quantum electrodynamics]].<ref>
{{cite book
 | last = Huang
 | first = K.
 | year = 2007
 | title = Fundamental Forces of Nature: The Story of Gauge Fields
 | url = https://books.google.com/books?id=q-CIFHpHxfEC&pg=PA123
 | pages = 123–125
 | publisher = [[World Scientific]]
 | isbn = 978-981-270-645-4
 | access-date = 2020-08-25
 | archive-date = 2022-02-04
 | archive-url = https://web.archive.org/web/20220204071144/https://books.google.com/books?id=q-CIFHpHxfEC&pg=PA123
 | url-status = live
}}</ref>

The apparent paradox in [[classical physics]] of a point particle electron having intrinsic angular momentum and magnetic moment can be explained by the formation of [[Virtual particle|virtual photons]] in the electric field generated by the electron. These photons can heuristically be thought of as causing the electron to shift about in a jittery fashion (known as [[zitterbewegung]]), which results in a net circular motion with [[precession]].<ref>
{{cite journal
 | last1 = Foldy | first1 = L.L.
 | last2 = Wouthuysen | first2 = S.
 | year = 1950
 | title = On the Dirac Theory of Spin 1/2 Particles and Its Non-Relativistic Limit
 | journal = [[Physical Review]]
 | volume = 78 | issue = 1 | pages = 29–36
 | doi = 10.1103/PhysRev.78.29
 |bibcode = 1950PhRv...78...29F
}}</ref> This motion produces both the spin and the magnetic moment of the electron.<ref name="curtis74" /> In atoms, this creation of virtual photons explains the [[Lamb shift]] observed in [[spectral line]]s.<ref name="genz" /> The Compton Wavelength shows that near elementary particles such as the electron, the uncertainty of the energy allows for the creation of virtual particles near the electron. This wavelength explains the "static" of virtual particles around elementary particles at a close distance.

=== Interaction ===
An electron generates an electric field that exerts an attractive force on a particle with a positive charge, such as the proton, and a repulsive force on a particle with a negative charge. The strength of this force in nonrelativistic approximation is determined by [[Coulomb's law|Coulomb's inverse square law]].<ref name=Griffiths1998>
{{cite book
 |last=Griffiths |first=David J.
 |title=Introduction to Electrodynamics |edition=3rd
 |publisher=Prentice Hall |year=1998
 |isbn=978-0-13-805326-0
 |url=https://archive.org/details/introductiontoel00grif_0
}}</ref>{{rp|pages=58–61}} When an electron is in motion, it generates a [[magnetic field]].<ref name="munowitz" />{{rp|page=140}} The [[Ampère's circuital law|Ampère–Maxwell law]] relates the magnetic field to the mass motion of electrons (the [[electric current|current]]) with respect to an observer. This property of induction supplies the magnetic field that drives an [[electric motor]].<ref>
{{cite book
 |last=Crowell
 |first=B.
 |title=Electricity and Magnetism
 |url=https://books.google.com/books?id=s9QWZNfnz1oC&pg=PT129
 |pages=129–152
 |publisher=Light and Matter
 |year=2000
 |isbn=978-0-9704670-4-1
 |access-date=2020-08-25
 |archive-date=2022-02-04
 |archive-url=https://web.archive.org/web/20220204083733/https://books.google.com/books?id=s9QWZNfnz1oC&pg=PT129
 |url-status=live
}}</ref> The electromagnetic field of an arbitrary moving charged particle is expressed by the [[Liénard–Wiechert potential]]s, which are valid even when the particle's speed is close to that of light ([[special relativity|relativistic]]).<ref name=Griffiths1998 />{{rp|pages=429–434}}

[[File:Lorentz force.svg|right|thumb|alt=A graph with arcs showing the motion of charged particles|A particle with charge ''q'' (at left) is moving with velocity ''v'' through a magnetic field ''B'' that is oriented toward the viewer. For an electron, ''q'' is negative, so it follows a curved trajectory toward the top.]]
When an electron is moving through a magnetic field, it is subject to the [[Lorentz force]] that acts perpendicularly to the plane defined by the magnetic field and the electron velocity. This [[centripetal force]] causes the electron to follow a [[Helix|helical]] trajectory through the field at a radius called the [[gyroradius]]. The acceleration from this curving motion induces the electron to radiate energy in the form of synchrotron radiation.<ref>
{{cite journal
 |last1 = Mahadevan |first1 = R.
 |last2 = Narayan |first2 = R.
 |last3 = Yi |first3 = I.
 |year = 1996
 |title = Harmony in Electrons: Cyclotron and Synchrotron Emission by Thermal Electrons in a Magnetic Field
 |journal = [[The Astrophysical Journal]]
 |volume = 465 | pages = 327–337
 |arxiv = astro-ph/9601073
 |doi = 10.1086/177422 |bibcode=1996ApJ...465..327M
 |s2cid = 16324613
}}</ref>{{efn|Radiation from non-relativistic electrons is sometimes termed [[cyclotron radiation]].}}<ref name=munowitz />{{rp|page=160}} The energy emission in turn causes a recoil of the electron, known as the [[Abraham–Lorentz force#Abraham–Lorentz–Dirac Force|Abraham–Lorentz–Dirac Force]], which creates a friction that slows the electron. This force is caused by a [[back-reaction]] of the electron's own field upon itself.<ref>
{{cite journal
 |last = Rohrlich |first = F.
 |year = 1999
 |title = The Self-Force and Radiation Reaction
 |journal = [[American Journal of Physics]]
 |volume = 68 |issue = 12 |pages = 1109–1112
 |doi = 10.1119/1.1286430
 |bibcode = 2000AmJPh..68.1109R
}}</ref>

[[File:Bremsstrahlung.svg|thumb|left|upright|alt=A curve shows the motion of the electron, a red dot shows the nucleus, and a wiggly line the emitted photon|Here, [[Bremsstrahlung]] is produced by an electron ''e'' deflected by the electric field of an atomic nucleus. The energy change ''E''<sub>2</sub>&nbsp;−&nbsp;''E''<sub>1</sub> determines the frequency ''f'' of the emitted photon.]]
Photons mediate electromagnetic interactions between particles in [[quantum electrodynamics]]. An isolated electron at a constant velocity cannot emit or absorb a real photon; doing so would violate [[conservation of energy]] and [[momentum]]. Instead, virtual photons can transfer momentum between two charged particles. This exchange of virtual photons, for example, generates the Coulomb force.<ref>
{{cite book
 |last=Georgi
 |first=H.
 |chapter=Grand Unified Theories
 |page=427
 |editor=Davies, Paul
 |title=The New Physics
 |chapter-url=https://books.google.com/books?id=akb2FpZSGnMC&pg=PA427
 |publisher=Cambridge University Press
 |year=1989
 |isbn=978-0-521-43831-5
 |access-date=2020-08-25
 |archive-date=2014-09-21
 |archive-url=https://web.archive.org/web/20140921171123/http://books.google.com/books?id=akb2FpZSGnMC&pg=PA427
 |url-status=live
}}</ref> Energy emission can occur when a moving electron is deflected by a charged particle, such as a proton. The deceleration of the electron results in the emission of [[Bremsstrahlung]] radiation.<ref>
{{cite journal
 |last1=Blumenthal |first1= G.J.
 |last2=Gould |first2=R.
 |year=1970
 |title=Bremsstrahlung, Synchrotron Radiation, and Compton Scattering of High-Energy Electrons Traversing Dilute Gases
 |journal=[[Reviews of Modern Physics]]
 |volume=42 |issue=2 |pages=237–270
 |doi=10.1103/RevModPhys.42.237 |bibcode=1970RvMP...42..237B
}}</ref>

An inelastic collision between a photon (light) and a solitary (free) electron is called [[Compton scattering]]. This collision results in a transfer of momentum and energy between the particles, which modifies the wavelength of the photon by an amount called the [[Compton scattering|Compton shift]].{{efn|The change in wavelength, Δ''λ'', depends on the angle of the recoil, ''θ'', as follows,
: <math>\textstyle \Delta \lambda = \frac{h}{m_{\mathrm{e}}c} (1 - \cos \theta),</math>
where ''c'' is the speed of light in vacuum and ''m''<sub>e</sub> is the electron mass. See Zombeck (2007).<ref name=Zombeck2007 />{{rp|page=393, 396}} }} The maximum magnitude of this wavelength shift is ''h''/''m''<sub>e</sub>''c'', which is known as the [[Compton wavelength]].<ref>
{{cite web
 |title=The Nobel Prize in Physics 1927
 |publisher=[[Nobel Foundation|The Nobel Foundation]]
 |year=2008
 |url=https://nobelprize.org/nobel_prizes/physics/laureates/1927/
 |access-date=2008-09-28
 |df=dmy-all
 |archive-date=2008-10-24
 |archive-url=https://web.archive.org/web/20081024124054/http://nobelprize.org/nobel_prizes/physics/laureates/1927/
 |url-status=live
}}</ref> For an electron, it has a value of {{val|2.43|e=-12|u=m}}.<ref name="CODATA" /> When the wavelength of the light is long (for instance, the wavelength of the [[Light|visible light]] is 0.4–0.7&nbsp;μm) the wavelength shift becomes negligible. Such interaction between the light and free electrons is called [[Thomson scattering]] or linear Thomson scattering.<ref name="Chen1998">
{{cite journal
 |last1=Chen |first1=S.-Y.
 |last2=Maksimchuk |first2=A.
 |last3=Umstadter |first3=D.
 |year=1998
 |title=Experimental observation of relativistic nonlinear Thomson scattering
 |journal=[[Nature (journal)|Nature]]
 |volume=396 |issue=6712 |pages=653–655
 |doi=10.1038/25303 |arxiv=physics/9810036
 |bibcode=1998Natur.396..653C|s2cid=16080209
}}</ref>

The relative strength of the electromagnetic interaction between two charged particles, such as an electron and a proton, is given by the [[fine-structure constant]]. This value is a dimensionless quantity formed by the ratio of two energies: the electrostatic energy of attraction (or repulsion) at a separation of one Compton wavelength, and the rest energy of the charge. It is given by {{physconst|alpha|symbol=yes|round=9|after=,}} which is approximately equal to {{sfrac|1|137}}.

When electrons and positrons collide, they [[Electron–positron annihilation|annihilate]] each other, giving rise to two or more gamma ray photons. If the electron and positron have negligible momentum, a [[Positronium|positronium atom]] can form before annihilation results in two or three gamma ray photons totalling 1.022&nbsp;MeV.<ref>
{{cite journal
 | last1 = Beringer | first1 = R.
 | last2 = Montgomery | first2 = C.G.
 | year = 1942
 | title = The Angular Distribution of Positron Annihilation Radiation
 | journal = [[Physical Review]]
 | volume = 61 | issue = 5–6 | pages = 222–224
 | doi = 10.1103/PhysRev.61.222
 | bibcode = 1942PhRv...61..222B }}</ref><ref>{{cite book
 | last = Buffa | first = A.
 | title = College Physics
 | publisher = Prentice Hall | edition = 4th | year = 2000
 | isbn = 978-0-13-082444-8
 | url = https://archive.org/details/collegephysicsvo00jerr/page/888
 | page =888
}}</ref> On the other hand, a high-energy photon can transform into an electron and a positron by a process called [[pair production]], but only in the presence of a nearby charged particle, such as a nucleus.<ref>
{{cite journal
 | last = Eichler | first = J.
 | year = 2005
 | title = Electron–positron pair production in relativistic ion–atom collisions
 | journal = [[Physics Letters A]]
 | volume = 347 | issue = 1–3 | pages = 67–72
 | doi = 10.1016/j.physleta.2005.06.105
 | bibcode = 2005PhLA..347...67E
}}</ref><ref>
{{cite journal
 | last = Hubbell
 | first = J.H.
 | year = 2006
 | title = Electron positron pair production by photons: A historical overview
 | journal = {{ill|Radiation Physics and Chemistry|fr}}
 | volume = 75
 | issue = 6
 | pages = 614–623
 | bibcode = 2006RaPC...75..614H
 | doi = 10.1016/j.radphyschem.2005.10.008
 | url = https://zenodo.org/record/1259327
 | access-date = 2019-06-21
 | archive-date = 2019-06-21
 | archive-url = https://web.archive.org/web/20190621192329/https://zenodo.org/record/1259327
 | url-status = live
}}</ref>

In the theory of [[electroweak interaction]], the [[Chirality (physics)|left-handed]] component of electron's wavefunction forms a [[weak isospin]] doublet with the [[Neutrino|electron neutrino]]. This means that during [[weak interaction]]s, electron neutrinos behave like electrons. Either member of this doublet can undergo a [[charged current]] interaction by emitting or absorbing a {{SubatomicParticle|W boson|link=yes}} and be converted into the other member. Charge is conserved during this reaction because the W&nbsp;boson also carries a charge, canceling out any net change during the transmutation. Charged current interactions are responsible for the phenomenon of [[beta decay]] in a [[Radioactive decay|radioactive]] atom. Both the electron and electron neutrino can undergo a [[neutral current]] interaction via a {{SubatomicParticle|Z boson0|link=yes}} exchange, and this is responsible for neutrino–electron [[elastic scattering]].<ref name="quigg">
{{cite conference
 |last=Quigg |first=C.
 |title=The Electroweak Theory |page=80
 |conference=TASI 2000: Flavor Physics for the Millennium
 |date=4–30 June 2000
 |place=Boulder, Colorado
 |arxiv=hep-ph/0204104 |bibcode = 2002hep.ph....4104Q
}}</ref>
{{clear}}

=== Atoms and molecules ===
{{Main|Atom}}
[[File:Hydrogen Density Plots.png|right|thumb|upright=1.25|alt=A table of five rows and five columns, with each cell portraying a color-coded probability density|Probability densities for the first few hydrogen atom orbitals, seen in cross-section. The energy level of a bound electron determines the orbital it occupies, and the color reflects the probability of finding the electron at a given position.]]
An electron can be ''bound'' to the nucleus of an atom by the attractive Coulomb force. A system of one or more electrons bound to a nucleus is called an atom. If the number of electrons is different from the nucleus's electrical charge, such an atom is called an [[ion]]. The wave-like behavior of a bound electron is described by a function called an [[atomic orbital]]. Each orbital has its own set of quantum numbers such as energy, angular momentum and projection of angular momentum, and only a discrete set of these orbitals exist around the nucleus. According to the Pauli exclusion principle each orbital can be occupied by up to two electrons, which must differ in their [[spin quantum number]].

Electrons can transfer between different orbitals by the emission or absorption of photons with an energy that matches the difference in potential.<ref name=Tipler2003 />{{rp|159–160}} Other methods of orbital transfer include collisions with particles, such as electrons, and the [[Auger effect]].<ref>
{{cite book
 | last = Burhop | first = E.H.S.
 | author-link = Eric Burhop
 | year = 1952
 | title = The Auger Effect and Other Radiationless Transitions
 | publisher = Cambridge University Press
 | pages = 2–3
 | isbn = 978-0-88275-966-1
}}</ref> To escape the atom, the energy of the electron must be increased above its [[Ionization energy|binding energy]] to the atom. This occurs, for example, with the [[photoelectric effect]], where an incident photon exceeding the atom's [[ionization energy]] is absorbed by the electron.<ref name=Tipler2003>
{{cite book
 | last1=Tipler | first1=Paul
 | last2=Llewellyn | first2=Ralph
 | title = Modern Physics
 | publisher=Macmillan | year=2003 | edition=illustrated
 | isbn=978-0-7167-4345-3
}}</ref>{{rp|127–132}}

The orbital angular momentum of electrons is [[Angular momentum operator#Quantization|quantized]]. Because the electron is charged, it produces an orbital magnetic moment that is proportional to the angular momentum. The net magnetic moment of an atom is equal to the vector sum of orbital and spin magnetic moments of all electrons and the nucleus. The magnetic moment of the nucleus is negligible compared with that of the electrons. The magnetic moments of the electrons that occupy the same orbital, called paired electrons, cancel each other out.<ref>
{{cite book
 | last = Jiles
 | first = D.
 | title = Introduction to Magnetism and Magnetic Materials
 | url = https://books.google.com/books?id=axyWXjsdorMC&pg=PA280
 | pages = 280–287
 | publisher = [[CRC Press]]
 | year = 1998
 | isbn = 978-0-412-79860-3
 | access-date = 2020-08-25
 | archive-date = 2021-01-26
 | archive-url = https://web.archive.org/web/20210126003325/https://books.google.com/books?id=axyWXjsdorMC&pg=PA280
 | url-status = live
}}</ref>

The [[chemical bond]] between atoms occurs as a result of electromagnetic interactions, as described by the laws of quantum mechanics.<ref>
{{cite book
 |last1        = Löwdin
 |first1       = P.O.
 |last2        = Erkki Brändas
 |first2       = E.
 |last3        = Kryachko
 |first3       = E.S.
 |title        = Fundamental World of Quantum Chemistry: A Tribute to the Memory of Per-Olov Löwdin
 |url          = https://books.google.com/books?id=8QiR8lCX_qcC&pg=PA393
 |pages        = 393–394
 |publisher    = Springer Science+Business Media
 |year         = 2003
 |isbn         = 978-1-4020-1290-7
 |access-date  = 2020-08-25
 |archive-date = 2022-02-04
 |archive-url  = https://web.archive.org/web/20220204071147/https://books.google.com/books?id=8QiR8lCX_qcC&pg=PA393
 |url-status   = live
}}</ref> The strongest bonds are formed by the [[Covalent bond|sharing]] or [[Electron transfer|transfer]] of electrons between atoms, allowing the formation of [[molecule]]s.<ref name=Pauling>
{{cite book
 | last = Pauling | first = L.C.
 | title = The Nature of the Chemical Bond and the Structure of Molecules and Crystals: an introduction to modern structural chemistry
 | url = https://archive.org/details/natureofchemical0000paul_3ed/page/4
 | url-access = registration | pages =4–10
 | publisher = Cornell University Press | edition = 3rd | year = 1960
 | isbn = 978-0-8014-0333-0
}}</ref> Within a molecule, electrons move under the influence of several nuclei, and occupy [[molecular orbital]]s; much as they can occupy atomic orbitals in isolated atoms.<ref>
{{cite book
 | last1 = McQuarrie
 | first1 = D.A.
 | last2 = Simon
 | first2 = J.D.
 | title = Physical Chemistry: A Molecular Approach
 | url = https://books.google.com/books?id=f-bje0-DEYUC&pg=PA325
 | publisher = University Science Books
 | year = 1997
 | pages = 325–361
 | isbn = 978-0-935702-99-6
 | access-date = 2020-08-25
 | archive-date = 2021-01-07
 | archive-url = https://web.archive.org/web/20210107160307/https://books.google.com/books?id=f-bje0-DEYUC&pg=PA325
 | url-status = live
}}</ref> A fundamental factor in these molecular structures is the existence of [[electron pair]]s. These are electrons with opposed spins, allowing them to occupy the same molecular orbital without violating the Pauli exclusion principle (much like in atoms). Different molecular orbitals have different spatial distribution of the electron density. For instance, in bonded pairs (i.e. in the pairs that actually bind atoms together) electrons can be found with the maximal probability in a relatively small volume between the nuclei. By contrast, in non-bonded pairs electrons are distributed in a large volume around nuclei.<ref
>{{cite journal
 |last=Daudel |first=R.
 |year=1974
 |title=The Electron Pair in Chemistry
 |journal=[[Canadian Journal of Chemistry]]
 |volume=52 |issue=8 |pages=1310–1320
 |doi=10.1139/v74-201
 |display-authors=etal
 |doi-access=free
}}</ref>

=== Conductivity ===
[[File:Lightning over Oradea Romania cropped.jpg|right|thumb|alt=Four bolts of lightning strike the ground|A [[lightning]] discharge consists primarily of a flow of electrons.<ref>
{{cite book
 | last1 = Rakov
 | first1 = V.A.
 | last2 = Uman
 | first2 = M.A.
 | title = Lightning: Physics and Effects
 | url = https://books.google.com/books?id=TuMa5lAa3RAC&pg=PA4
 | page = 4
 | publisher = Cambridge University Press
 | year = 2007
 | isbn = 978-0-521-03541-5
 | access-date = 2020-08-25
 | archive-date = 2021-01-26
 | archive-url = https://web.archive.org/web/20210126003319/https://books.google.com/books?id=TuMa5lAa3RAC&pg=PA4
 | url-status = live
}}</ref> The electric potential needed for lightning can be generated by a triboelectric effect.<ref>
{{cite journal
 | last1 = Freeman | first1 = G.R.
 | last2 = March | first2 = N.H.
 | year = 1999
 | title = Triboelectricity and some associated phenomena
 | journal = Materials Science and Technology
 | volume = 15 | issue = 12 | pages = 1454–1458
 | doi = 10.1179/026708399101505464
 | bibcode = 1999MatST..15.1454F
}}</ref><ref>
{{cite journal
 | last1 = Forward | first1 = K.M.
 | last2 = Lacks | first2 = D.J.
 | last3 = Sankaran | first3 = R.M.
 | year = 2009
 | title = Methodology for studying particle–particle triboelectrification in granular materials
 | journal = {{ill|Journal of Electrostatics|tr}}
 | volume = 67 | issue = 2–3 | pages = 178–183
 | doi = 10.1016/j.elstat.2008.12.002
}}</ref>]]
If a body has more or fewer electrons than are required to balance the positive charge of the nuclei, then that object has a net electric charge. When there is an excess of electrons, the object is said to be negatively charged. When there are fewer electrons than the number of protons in nuclei, the object is said to be positively charged. When the number of electrons and the number of protons are equal, their charges cancel each other and the object is said to be electrically neutral. A macroscopic body can develop an electric charge through rubbing, by the [[triboelectric effect]].<ref>
{{cite book
 | last = Weinberg | first = S.
 | title = The Discovery of Subatomic Particles
 | url = https://archive.org/details/discoveryofsubat00wein_0/page/15
 | url-access = registration | pages =15–16
 | publisher = Cambridge University Press | year = 2003
 | isbn = 978-0-521-82351-7
}}</ref>

Independent electrons moving in vacuum are termed ''free'' electrons. Electrons in metals also behave as if they were free. In reality the particles that are commonly termed electrons in metals and other solids are quasi-electrons—[[quasiparticle]]s, which have the same electrical charge, spin, and magnetic moment as real electrons but might have a different mass.<ref name="Liang-fu Lou">
{{cite book
 | last = Lou
 | first = L.-F.
 | title = Introduction to phonons and electrons
 | url = https://books.google.com/books?id=XMv-vfsoRF8C&pg=PA162
 | pages = 162, 164
 | publisher = [[World Scientific]]
 | year = 2003
 | isbn = 978-981-238-461-4
 | bibcode = 2003ipe..book.....L
 | access-date = 2020-08-25
 | archive-date = 2022-02-04
 | archive-url = https://web.archive.org/web/20220204071149/https://books.google.com/books?id=XMv-vfsoRF8C&pg=PA162
 | url-status = live
}}</ref> When free electrons—both in vacuum and metals—move, they produce a [[Flow network|net flow]] of charge called an [[electric current]], which generates a magnetic field. Likewise a current can be created by a changing magnetic field. These interactions are described mathematically by [[Maxwell's equations]].<ref>
{{cite book
 | last1 = Guru
 | first1 = B.S.
 | last2 = Hızıroğlu
 | first2 = H.R.
 | title = Electromagnetic Field Theory Fundamentals
 | url = https://archive.org/details/electromagneticf0000bhag
 | pages = 138, 276
 | publisher = Cambridge University Press
 | year = 2004
 | isbn = 978-0-521-83016-4
 | url-access=registration
}}</ref>

At a given temperature, each material has an [[Electrical resistivity and conductivity|electrical conductivity]] that determines the value of electric current when an [[electric potential]] is applied. Examples of good conductors include metals such as copper and gold, whereas glass and [[Polytetrafluoroethylene|Teflon]] are poor conductors. In any [[dielectric]] material, the electrons remain bound to their respective atoms and the material behaves as an [[Insulator (electricity)|insulator]]. Most [[semiconductor]]s have a variable level of conductivity that lies between the extremes of conduction and insulation.<ref>
{{cite book
 | last1 = Achuthan
 | first1 = M.K.
 | last2 = Bhat
 | first2 = K.N.
 | title = Fundamentals of Semiconductor Devices
 | url = https://books.google.com/books?id=REQkwBF4cVoC&pg=PA49
 | pages = 49–67
 | publisher = [[Tata McGraw-Hill]]
 | year = 2007
 | isbn = 978-0-07-061220-4
 | access-date = 2020-08-25
 | archive-date = 2021-01-07
 | archive-url = https://web.archive.org/web/20210107160319/https://books.google.com/books?id=REQkwBF4cVoC&pg=PA49
 | url-status = live
}}</ref> On the other hand, [[metallic bond|metals]] have an [[electronic band structure]] containing partially filled electronic bands. The presence of such bands allows electrons in metals to behave as if they were free or [[delocalized electron]]s. These electrons are not associated with specific atoms, so when an electric field is applied, they are free to move like a gas (called [[Fermi gas]])<ref name="ziman">
{{cite book
 | last = Ziman
 | first = J.M.
 | title = Electrons and Phonons: The Theory of Transport Phenomena in Solids
 | url = https://books.google.com/books?id=UtEy63pjngsC&pg=PA260
 | publisher = Oxford University Press
 | year = 2001
 | page = 260
 | isbn = 978-0-19-850779-6
 | access-date = 2020-08-25
 | archive-date = 2022-02-24
 | archive-url = https://web.archive.org/web/20220224105543/https://books.google.com/books?id=UtEy63pjngsC&pg=PA260
 | url-status = live
}}</ref> through the material much like free electrons.

Because of collisions between electrons and atoms, the [[drift velocity]] of electrons in a conductor is on the order of millimeters per second. However, the speed at which a change of current at one point in the material causes changes in currents in other parts of the material, the [[Wave propagation speed|velocity of propagation]], is typically about 75% of light speed.<ref>
{{cite journal
 | last = Main
 | first = P.
 | date = June 12, 1993
 | title = When electrons go with the flow: Remove the obstacles that create electrical resistance, and you get ballistic electrons and a quantum surprise
 | journal = [[New Scientist]]
 | volume = 1887
 | page = 30
 | url = https://www.newscientist.com/article/mg13818774.500-when-electrons-go-with-the-flow-remove-the-obstacles-thatcreate-electrical-resistance-and-you-get-ballistic-electrons-and-a-quantumsurprise.html
 | access-date = 2008-10-09
 | df = dmy-all
 | archive-date = 2015-02-11
 | archive-url = https://web.archive.org/web/20150211085229/http://www.newscientist.com/article/mg13818774.500-when-electrons-go-with-the-flow-remove-the-obstacles-thatcreate-electrical-resistance-and-you-get-ballistic-electrons-and-a-quantumsurprise.html
 | url-status = live
}}</ref> This occurs because electrical signals propagate as a wave, with the velocity dependent on the [[Relative permittivity|dielectric constant]] of the material.<ref>
{{cite book
 | last = Blackwell
 | first = G.R.
 | title = The Electronic Packaging Handbook
 | url = https://books.google.com/books?id=D0PBG53PQlUC&pg=SA6-PA39
 | pages = 6.39–6.40
 | publisher = [[CRC Press]]
 | year = 2000
 | isbn = 978-0-8493-8591-9
 | access-date = 2020-08-25
 | archive-date = 2022-02-04
 | archive-url = https://web.archive.org/web/20220204083743/https://books.google.com/books?id=D0PBG53PQlUC&pg=SA6-PA39
 | url-status = live
}}</ref>

Metals make relatively good conductors of heat, primarily because the delocalized electrons are free to transport thermal energy between atoms. However, unlike electrical conductivity, the thermal conductivity of a metal is nearly independent of temperature. This is expressed mathematically by the [[Wiedemann–Franz law]],<ref name="ziman" /> which states that the ratio of [[thermal conductivity]] to the electrical conductivity is proportional to the temperature. The thermal disorder in the metallic lattice increases the electrical [[Electrical resistivity and conductivity|resistivity]] of the material, producing a temperature dependence for electric current.<ref name="durrant">
{{cite book
 | last = Durrant
 | first = A.
 | title = Quantum Physics of Matter: The Physical World
 | url = https://books.google.com/books?id=F0JmHRkJHiUC&pg=PA43
 | pages = 43, 71–78
 | publisher = CRC Press
 | year = 2000
 | isbn = 978-0-7503-0721-5
 | access-date = 2015-10-16
 | archive-date = 2016-05-27
 | archive-url = https://web.archive.org/web/20160527150628/https://books.google.com/books?id=F0JmHRkJHiUC&pg=PA43
 | url-status = live
}}</ref>

When cooled below a point called the [[Critical point (thermodynamics)|critical temperature]], materials can undergo a phase transition in which they lose all resistivity to electric current, in a process known as [[superconductivity]]. In [[BCS theory]], pairs of electrons called [[Cooper pair]]s have their motion coupled to nearby matter via lattice vibrations called [[phonon]]s, thereby avoiding the collisions with atoms that normally create electrical resistance.<ref>
{{cite web
 | title = The Nobel Prize in Physics 1972
 | publisher = [[Nobel Foundation|The Nobel Foundation]]
 | year = 2008
 | url = https://nobelprize.org/nobel_prizes/physics/laureates/1972/
 | access-date = 2008-10-13
 | df = dmy-all
 | archive-date = 2008-10-11
 | archive-url = https://web.archive.org/web/20081011050516/http://nobelprize.org/nobel_prizes/physics/laureates/1972/
 | url-status = live
}}</ref> (Cooper pairs have a radius of roughly 100&nbsp;nm, so they can overlap each other.)<ref>
{{cite journal
 | last = Kadin | first = A.M.
 | title = Spatial Structure of the Cooper Pair
 | journal = {{ill|Journal of Superconductivity and Novel Magnetism|tr}}
 | year = 2007
 | volume = 20 | issue = 4 | pages = 285–292
 | arxiv = cond-mat/0510279
 | doi =10.1007/s10948-006-0198-z
 | s2cid = 54948290
}}</ref> However, the mechanism by which [[unconventional superconductor|higher temperature superconductors]] operate remains uncertain.

Electrons inside conducting solids, which are quasi-particles themselves, when tightly confined at temperatures close to [[absolute zero]], behave as though they had split into three other [[quasiparticle]]s: [[spinon]]s, [[orbiton]]s and [[holon (physics)|holons]].<ref>
{{cite web
 | title = Discovery about behavior of building block of nature could lead to computer revolution
 | date = July 31, 2009
 | website = [[Science Daily|ScienceDaily]]
 | url = https://www.sciencedaily.com/releases/2009/07/090730141607.htm
 | access-date = 2009-08-01
 | df = dmy-all
 | archive-date = 2019-04-04
 | archive-url = https://web.archive.org/web/20190404130054/https://www.sciencedaily.com/releases/2009/07/090730141607.htm
 | url-status = live
}}</ref><ref>
{{cite journal
 | last1 = Jompol | first1 = Y.  |display-authors=etal
 | year = 2009
 | title = Probing Spin-Charge Separation in a Tomonaga-Luttinger Liquid
 | journal = [[Science (journal)|Science]]
 | volume = 325 | issue = 5940 | pages = 597–601
 | doi =10.1126/science.1171769
 | pmid =19644117 | bibcode = 2009Sci...325..597J |arxiv = 1002.2782
 | s2cid = 206193
}}</ref> The former carries spin and magnetic moment, the next carries its orbital location while the latter electrical charge.

=== Motion and energy ===
According to [[Albert Einstein|Einstein's]] theory of [[special relativity]], as an electron's speed approaches the [[speed of light]], from an observer's point of view its [[Mass in special relativity|relativistic mass]] increases, thereby making it more and more difficult to accelerate it from within the observer's frame of reference. The speed of an electron can approach, but never reach, the speed of light in vacuum, ''c''. However, when relativistic electrons—that is, electrons moving at a speed close to ''c''—are injected into a dielectric medium such as water, where the local speed of light is significantly less than ''c'', the electrons temporarily travel faster than light in the medium. As they interact with the medium, they generate a faint light called [[Cherenkov radiation]].<ref>
{{cite web
 | title = The Nobel Prize in Physics 1958, for the discovery and the interpretation of the Cherenkov effect
 | publisher = [[Nobel Foundation|The Nobel Foundation]]
 | year = 2008
 | url = https://nobelprize.org/nobel_prizes/physics/laureates/1958/
 | access-date = 2008-09-25
 | df = dmy-all
 | archive-date = 2008-10-18
 | archive-url = https://web.archive.org/web/20081018162638/http://nobelprize.org/nobel_prizes/physics/laureates/1958/
 | url-status = live
}}</ref>

[[File:Lorentz factor.svg|thumb|right|alt=The plot starts at zero and curves sharply upward toward the right|Lorentz factor as a function of velocity. It starts at value 1 and goes to infinity as ''v'' approaches ''c''.]]
The effects of special relativity are based on a quantity known as the [[Lorentz factor]], defined as <math>\scriptstyle\gamma=1/ \sqrt{ 1-{v^2}/{c^2} }</math> where ''v'' is the speed of the particle. The kinetic energy ''K''<sub>e</sub> of an electron moving with velocity ''v'' is:
:<math>\displaystyle K_{\mathrm{e}} = (\gamma - 1)m_{\mathrm{e}} c^2,</math>
where ''m''<sub>e</sub> is the mass of electron. For example, the [[SLAC National Accelerator Laboratory|Stanford linear accelerator]] can [[Acceleration|accelerate]] an electron to roughly 51&nbsp;GeV.<ref>
{{cite web
 | date = August 26, 2008
 | title = Special Relativity
 | publisher = [[SLAC National Accelerator Laboratory|Stanford Linear Accelerator Center]]
 | url = https://www2.slac.stanford.edu/vvc/theory/relativity.html
 | access-date = 2008-09-25
 | df = dmy-all
 | archive-date = 2008-08-28
 | archive-url = https://web.archive.org/web/20080828113927/http://www2.slac.stanford.edu/VVC/theory/relativity.html
 | url-status = live
}}</ref>
Since an electron behaves as a wave, at a given velocity it has a characteristic [[Matter wave|de Broglie wavelength]]. This is given by ''λ''<sub>e</sub>&nbsp;=&nbsp;''h''/''p'' where ''h'' is the [[Planck constant]] and ''p'' is the momentum.<ref name="de_broglie" /> For the 51&nbsp;GeV electron above, the wavelength is about {{val|2.4|e=-17|u=m}}, small enough to explore structures well below the size of an atomic nucleus.<ref>
{{cite book
 | last = Adams
 | first = S.
 | title = Frontiers: Twentieth Century Physics
 | url = https://books.google.com/books?id=yIsMaQblCisC&pg=PA215
 | page = 215
 | publisher = [[CRC Press]]
 | year = 2000
 | isbn = 978-0-7484-0840-5
 | access-date = 2020-08-25
 | archive-date = 2022-02-04
 | archive-url = https://web.archive.org/web/20220204071142/https://books.google.com/books?id=yIsMaQblCisC&pg=PA215
 | url-status = live
}}</ref>

== Formation ==
[[File:Pair production.png|right|thumb|alt=A photon approaches the nucleus from the left, with the resulting electron and positron moving off to the right|[[Pair production]] of an electron and positron, caused by the close approach of a photon with an atomic nucleus. The lightning symbol represents an exchange of a virtual photon, thus an electric force acts. The angle between the particles is very small.<ref>
{{cite book
 |title=Selected Exercises in Particle and Nuclear Physics
 |first1=Lorenzo
 |last1=Bianchini
 |publisher=Springer
 |year=2017
 |isbn=978-3-319-70494-4
 |page=79
 |url=https://books.google.com/books?id=lktADwAAQBAJ&pg=PA79
 |access-date=2018-04-20
 |archive-date=2020-01-02
 |archive-url=https://web.archive.org/web/20200102022221/https://books.google.com/books?id=lktADwAAQBAJ&pg=PA79
 |url-status=live
}}</ref>]]

<!-- Big bang theory with focus on the electron -->
The [[Big Bang]] theory is the most widely accepted scientific theory to explain the early stages in the evolution of the Universe.<ref>
{{cite book
 | last = Lurquin | first = P.F.
 | title = The Origins of Life and the Universe
 | url=https://archive.org/details/originsoflifet00paul/page/2 |url-access=registration |page=2
 | publisher = Columbia University Press | year = 2003
 | isbn = 978-0-231-12655-7
}}</ref> For the first millisecond of the Big Bang, the temperatures were over 10&nbsp;billion&nbsp;[[kelvin]]s and photons had mean energies over a million [[electronvolt]]s. These photons were sufficiently energetic that they could react with each other to form pairs of electrons and positrons. Likewise, positron–electron pairs annihilated each other and emitted energetic photons:
: {{SubatomicParticle|photon|link=yes}} + {{SubatomicParticle|photon}} ↔ {{SubatomicParticle|positron|link=yes}} + {{SubatomicParticle|electron}}
An equilibrium between electrons, positrons and photons was maintained during this phase of the evolution of the Universe. After 15 seconds had passed, however, the temperature of the universe dropped below the threshold where electron-positron formation could occur. Most of the surviving electrons and positrons annihilated each other, releasing gamma radiation that briefly reheated the universe.<ref>
{{cite book
 | last = Silk | first = J.
 | title = The Big Bang: The Creation and Evolution of the Universe
 | pages = 110–112, 134–137
 | publisher = Macmillan | edition = 3rd | year = 2000
 | isbn = 978-0-8050-7256-3
}}</ref>

For reasons that remain uncertain, during the annihilation process there was an excess in the number of particles over antiparticles. Hence, about one electron for every billion electron–positron pairs survived. This excess matched the excess of protons over antiprotons, in a condition known as [[baryon asymmetry]], resulting in a net charge of zero for the universe.<ref>
{{cite journal
 | last1 = Kolb
 | first1 = E.W.
 | last2 = Wolfram
 | first2 = Stephen
 | year = 1980
 | title = The Development of Baryon Asymmetry in the Early Universe
 | journal = [[Physics Letters B]]
 | volume = 91
 | issue = 2
 | pages = 217–221
 | doi = 10.1016/0370-2693(80)90435-9
 | bibcode = 1980PhLB...91..217K
 | s2cid = 122680284
 | url = https://authors.library.caltech.edu/99675/2/Development%20of%20Baryon%20Asymmetry%20in%20the%20Early%20Universe.pdf
 | access-date = 2020-08-25
 | archive-date = 2020-10-30
 | archive-url = https://web.archive.org/web/20201030105942/https://authors.library.caltech.edu/99675/2/Development%20of%20Baryon%20Asymmetry%20in%20the%20Early%20Universe.pdf
 | url-status = live
}}</ref><ref>
{{cite web
 | last = Sather
 | first = E.
 | date = Spring–Summer 1996
 | title = The Mystery of Matter Asymmetry
 | url = https://www.slac.stanford.edu/pubs/beamline/26/1/26-1-sather.pdf
 | periodical = Beam Line
 | publisher = Stanford University
 | access-date = 2008-11-01
 | df = dmy-all
 | archive-date = 2008-10-12
 | archive-url = https://web.archive.org/web/20081012012543/http://www.slac.stanford.edu/pubs/beamline/26/1/26-1-sather.pdf
 | url-status = live
}}</ref> The surviving protons and neutrons began to participate in reactions with each other—in the process known as [[nucleosynthesis]], forming isotopes of hydrogen and [[helium]], with trace amounts of [[lithium]]. This process peaked after about five minutes.<ref>
{{cite arXiv
 | last1 = Burles | first1 = S.
 | last2 = Nollett | first2 = K.M.
 | last3 = Turner | first3 = M.S.
 | year = 1999
 | title = Big-Bang Nucleosynthesis: Linking Inner Space and Outer Space
 |eprint=astro-ph/9903300
}}</ref> Any leftover neutrons underwent negative [[beta decay]] with a half-life of about a thousand seconds, releasing a proton and electron in the process,
: {{SubatomicParticle|Neutron|link=yes}} → {{SubatomicParticle|Proton|link=yes}} + {{SubatomicParticle|Electron}} + {{SubatomicParticle|Electron antineutrino|link=yes}}
For about the next {{val|300000}}–{{val|400000|u=years}}, the excess electrons remained too energetic to bind with [[Atomic nucleus|atomic nuclei]].<ref>
{{cite journal
 | last1 = Boesgaard | first1 = A.M.
 | last2 = Steigman | first2 = G.
 | year = 1985
 | title = Big bang nucleosynthesis&nbsp;– Theories and observations
 | journal = [[Annual Review of Astronomy and Astrophysics]]
 | volume = 23 | issue = 2 | pages = 319–378
 | bibcode =1985ARA&A..23..319B
 | doi =10.1146/annurev.aa.23.090185.001535
}}</ref> What followed is a period known as [[Chronology of the universe#Recombination, photon decoupling, and the cosmic microwave background (CMB)|recombination]], when neutral atoms were formed and the expanding universe became transparent to radiation.<ref name="science5789">
{{cite journal
 | last = Barkana | first = R.
 | year = 2006
 | title = The First Stars in the Universe and Cosmic Reionization
 | journal = [[Science (journal)|Science]]
 | volume = 313 | issue = 5789 | pages = 931–934
 | doi =10.1126/science.1125644
 | pmid =16917052 |arxiv = astro-ph/0608450
 | bibcode = 2006Sci...313..931B | citeseerx = 10.1.1.256.7276
 | s2cid = 8702746
}}</ref>

<!-- Stellar -->
Roughly one million years after the big bang, the first generation of [[star]]s began to form.<ref name="science5789" /> Within a star, [[stellar nucleosynthesis]] results in the production of positrons from the fusion of atomic nuclei. These antimatter particles immediately annihilate with electrons, releasing gamma rays. The net result is a steady reduction in the number of electrons, and a matching increase in the number of neutrons. However, the process of [[stellar evolution]] can result in the synthesis of radioactive isotopes. Selected isotopes can subsequently undergo negative beta decay, emitting an electron and antineutrino from the nucleus.<ref>{{cite journal | last1 = Burbidge | first1 = E.M. | display-authors = etal | year = 1957 | title = Synthesis of Elements in Stars | journal = [[Reviews of Modern Physics]] | volume = 29 | issue = 4 | pages = 548–647 | doi = 10.1103/RevModPhys.29.547 | bibcode = 1957RvMP...29..547B | url = https://authors.library.caltech.edu/45747/1/BURrmp57.pdf | doi-access = free | access-date = 2019-06-21 | archive-date = 2018-07-23 | archive-url = https://web.archive.org/web/20180723054833/https://authors.library.caltech.edu/45747/1/BURrmp57.pdf | url-status = live }}</ref> An example is the [[cobalt-60]] (<sup>60</sup>Co) isotope, which decays to form [[Isotopes of nickel|nickel-60]] ({{SimpleNuclide|Nickel|60}}).<ref>
{{cite journal
 | last1 = Rodberg | first1 = L.S.
 | last2 = Weisskopf | first2 = V.
 | year = 1957
 | title = Fall of Parity: Recent Discoveries Related to Symmetry of Laws of Nature
 | journal = [[Science (journal)|Science]]
 | volume = 125 | issue = 3249 | pages = 627–633
 | doi =10.1126/science.125.3249.627 | pmid =17810563
 | bibcode = 1957Sci...125..627R
}}</ref>
[[File:AirShower.svg|left|thumb|alt=A branching tree representing the particle production|An extended air shower generated by an energetic cosmic ray striking the Earth's atmosphere]]
At the end of its lifetime, a star with more than about 20 [[solar mass]]es can undergo [[gravitational collapse]] to form a [[black hole]].<ref>
{{cite journal
 | last = Fryer | first = C.L.
 | year = 1999
 | title = Mass Limits For Black Hole Formation
 | journal = [[The Astrophysical Journal]]
 | volume = 522 | issue = 1 | pages = 413–418
 | bibcode = 1999ApJ...522..413F
 | doi =10.1086/307647
 | arxiv = astro-ph/9902315 | s2cid = 14227409
}}</ref> According to [[classical physics]], these massive stellar objects exert a [[Gravitation|gravitational attraction]] that is strong enough to prevent anything, even [[electromagnetic radiation]], from escaping past the [[Schwarzschild radius]]. However, quantum mechanical effects are believed to potentially allow the emission of [[Hawking radiation]] at this distance. Electrons (and positrons) are thought to be created at the [[event horizon]] of these [[Compact star|stellar remnants]].

When a pair of virtual particles (such as an electron and positron) is created in the vicinity of the event horizon, random spatial positioning might result in one of them to appear on the exterior; this process is called [[quantum tunnelling]]. The [[gravitational potential]] of the black hole can then supply the energy that transforms this virtual particle into a real particle, allowing it to radiate away into space.<ref>
{{cite journal
 |last1   = Parikh |first1  = M.K.
 |last2   = Wilczek |first2  = F.
 |year    = 2000
 |title   = Hawking Radiation As Tunneling
 |journal = [[Physical Review Letters]]
 |volume  = 85 |issue   = 24 |pages   = 5042–5045
 |doi = 10.1103/PhysRevLett.85.5042 |pmid = 11102182 |hdl = 1874/17028
 |bibcode = 2000PhRvL..85.5042P |arxiv = hep-th/9907001
 |s2cid = 8013726
}}</ref> In exchange, the other member of the pair is given negative energy, which results in a net loss of mass–energy by the black hole. The rate of Hawking radiation increases with decreasing mass, eventually causing the black hole to evaporate away until, finally, it explodes.<ref>
{{cite journal
 | last = Hawking | first = S.W.
 | year = 1974
 | title = Black hole explosions?
 | journal = [[Nature (journal)|Nature]]
 | volume = 248 | issue=5443 | pages = 30–31
 | doi =10.1038/248030a0 |bibcode = 1974Natur.248...30H
 | s2cid = 4290107
}}</ref>

<!-- Other sources -->
[[Cosmic ray]]s are particles traveling through space with high energies. Energy events as high as {{val|3.0|e=20|u=eV}} have been recorded.<ref>
{{cite journal
 | last1 = Halzen | first1 = F. | author-link1 = Francis Halzen
 | last2 = Hooper | first2 = D.
 | year = 2002
 | title = High-energy neutrino astronomy: the cosmic ray connection
 | journal = [[Reports on Progress in Physics]]
 | volume = 66 | issue = 7 | pages = 1025–1078
 | bibcode = 2002RPPh...65.1025H |arxiv = astro-ph/0204527
 | doi =10.1088/0034-4885/65/7/201
 | s2cid = 53313620
}}</ref> When these particles collide with nucleons in the [[Atmosphere of Earth|Earth's atmosphere]], a shower of particles is generated, including [[pion]]s.<ref>
{{cite journal
 | last = Ziegler | first = J.F.
 | year = 1998
 | title = Terrestrial cosmic ray intensities
 | journal = [[IBM Journal of Research and Development]]
 | volume = 42 | issue = 1 | pages = 117–139
 | doi =10.1147/rd.421.0117 | bibcode = 1998IBMJ...42..117Z
}}</ref> More than half of the cosmic radiation observed from the Earth's surface consists of [[muon]]s. The particle called a muon is a lepton produced in the upper atmosphere by the decay of a pion.
: {{SubatomicParticle|Pion-|link=yes}} → {{SubatomicParticle|Muon|link=yes}} + {{SubatomicParticle|Muon antineutrino|link=yes}}
A muon, in turn, can decay to form an electron or positron.<ref>
{{cite news
 | last = Sutton
 | first = C.
 | date = August 4, 1990
 | title = Muons, pions and other strange particles
 | url = https://www.newscientist.com/article/mg12717284.700-muons-pions-and-other-strange-particles-.html
 | magazine = [[New Scientist]]
 | access-date = 2008-08-28
 | df = dmy-all
 | archive-date = 2015-02-11
 | archive-url = https://web.archive.org/web/20150211085842/http://www.newscientist.com/article/mg12717284.700-muons-pions-and-other-strange-particles-.html
 | url-status = live
}}</ref>
: {{SubatomicParticle|Muon}} → {{SubatomicParticle|Electron}} + {{SubatomicParticle|Electron antineutrino|link=yes}} + {{SubatomicParticle|Muon neutrino|link=yes}}

== Observation ==
[[File:Aurore australe - Aurora australis.jpg|right|thumb|alt=A swirling green glow in the night sky above snow-covered ground|[[Aurora (astronomy)|Aurorae]] are mostly caused by energetic electrons precipitating into the [[atmosphere]]<ref>
{{cite press release
 |last=Wolpert |first=S.
 |date=July 24, 2008
 |title=Scientists solve 30&nbsp;year-old aurora borealis mystery
 |publisher=University of California
 |url=https://www.universityofcalifornia.edu/news/article/18277
 |url-status=dead |access-date=2008-10-11 |df=dmy-all
 |archive-url=https://web.archive.org/web/20080817094058/https://www.universityofcalifornia.edu/news/article/18277
 |archive-date=August 17, 2008
}}</ref>]]
Remote observation of electrons requires detection of their radiated energy. For example, in high-energy environments such as the [[stellar corona|corona]] of a star, free electrons form a [[Plasma (physics)|plasma]] that radiates energy due to [[Bremsstrahlung]] radiation. Electron gas can undergo [[plasma oscillation]], which is waves caused by synchronized variations in electron density, and these produce energy emissions that can be detected by using [[radio telescope]]s.<ref>
{{cite journal
 | last1 = Gurnett | first1 = D.A.
 | last2 = Anderson | first2 = R.
 | year = 1976
 | title = Electron Plasma Oscillations Associated with Type III Radio Bursts
 | journal = [[Science (journal)|Science]]
 | volume = 194 | issue = 4270 | pages = 1159–1162
 | doi =10.1126/science.194.4270.1159 | pmid =17790910
 | bibcode = 1976Sci...194.1159G | s2cid = 11401604
}}</ref>

The [[frequency]] of a [[photon]] is proportional to its energy. As a bound electron transitions between different energy levels of an atom, it absorbs or emits photons at characteristic frequencies. For instance, when atoms are irradiated by a source with a broad spectrum, distinct [[spectral line|dark lines]] appear in the spectrum of transmitted radiation in places where the corresponding frequency is absorbed by the atom's electrons. Each element or molecule displays a characteristic set of spectral lines, such as the [[hydrogen spectral series]]. When detected, [[Spectroscopy|spectroscopic]] measurements of the strength and width of these lines allow the composition and physical properties of a substance to be determined.<ref>
{{cite web
 | last1 = Martin
 | first1 = W.C.
 | last2 = Wiese
 | first2 = W.L.
 | year = 2007
 | title = Atomic Spectroscopy: A compendium of basic ideas, notation, data, and formulas
 | publisher = [[National Institute of Standards and Technology]]
 | access-date = 2007-01-08
 | df = dmy-all
 | url = https://physics.nist.gov/Pubs/AtSpec/
 | archive-date = 2007-02-08
 | archive-url = https://web.archive.org/web/20070208113156/http://physics.nist.gov/Pubs/AtSpec/
 | url-status = live
}}</ref><ref>
{{cite book
 | last = Fowles
 | first = G.R.
 | title = Introduction to Modern Optics
 | pages = 227–233
 | publisher = [[Courier Dover]]
 | year = 1989
 | isbn = 978-0-486-65957-2
 | url = https://books.google.com/books?id=SL1n9TuJ5YMC&pg=PA227
 | access-date = 2020-08-25
 | archive-date = 2021-01-07
 | archive-url = https://web.archive.org/web/20210107160307/https://books.google.com/books?id=SL1n9TuJ5YMC&pg=PA227
 | url-status = live
}}</ref>

In laboratory conditions, the interactions of individual electrons can be observed by means of [[particle detector]]s, which allow measurement of specific properties such as energy, spin and charge.<ref name="grupen">
{{cite journal
 | last = Grupen | first = C.
 | year = 2000
 | title = Physics of Particle Detection
 | journal = [[AIP Conference Proceedings]]
 | volume = 536 | pages = 3–34
 | doi =10.1063/1.1361756 |arxiv = physics/9906063
 | bibcode = 2000AIPC..536....3G
 | s2cid = 119476972
}}</ref> The development of the [[quadrupole ion trap|Paul trap]] and [[Penning trap]] allows charged particles to be contained within a small region for long durations. This enables precise measurements of the particle properties. For example, in one instance a Penning trap was used to contain a single electron for a period of 10 months.<ref name="nobel1989">
{{cite web
 | title = The Nobel Prize in Physics 1989
 | publisher = [[Nobel Foundation|The Nobel Foundation]]
 | year = 2008
 | url = https://nobelprize.org/nobel_prizes/physics/laureates/1989/illpres/
 | access-date = 2008-09-24
 | df = dmy-all
 | archive-date = 2008-09-28
 | archive-url = https://web.archive.org/web/20080928042325/http://nobelprize.org/nobel_prizes/physics/laureates/1989/illpres/
 | url-status = live
}}</ref> The magnetic moment of the electron was measured to a precision of eleven digits, which, in 1980, was a greater accuracy than for any other physical constant.<ref>
{{cite journal
 | last1 = Ekstrom
 | first1 = P.
 | last2 = Wineland
 | first2 = David
 | year = 1980
 | title = The isolated Electron
 | journal = [[Scientific American]]
 | volume = 243
 | issue = 2
 | pages = 91–101
 | url = https://tf.nist.gov/general/pdf/166.pdf
 | access-date = 2008-09-24
 | df = dmy-all
 | doi = 10.1038/scientificamerican0880-104
 | bibcode = 1980SciAm.243b.104E
 | archive-date = 2019-09-16
 | archive-url = https://web.archive.org/web/20190916211444/https://tf.nist.gov/general/pdf/166.pdf
 | url-status = live
}}</ref>

The first video images of an electron's energy distribution were captured by a team at [[Lund University]] in Sweden, February 2008. The scientists used extremely short flashes of light, called [[attosecond]] pulses, which allowed an electron's motion to be observed for the first time.<ref>
{{cite web
 | last = Mauritsson | first = J.
 | title = Electron filmed for the first time ever
 | url = https://www.atto.fysik.lth.se/video/pressrelen.pdf
 | publisher = [[Lund University]]
 | access-date = 2008-09-17 |df=dmy-all
 | archive-url = https://web.archive.org/web/20090325194101/https://www.atto.fysik.lth.se/video/pressrelen.pdf
 | archive-date = March 25, 2009
}}</ref><ref name=Mauritsson>
{{cite journal
 | last1 = Mauritsson | first1 = J. |display-authors=etal
 | year = 2008
 | title = Coherent Electron Scattering Captured by an Attosecond Quantum Stroboscope
 | journal = [[Physical Review Letters]]
 | volume = 100 | issue = 7 | page = 073003
 | doi =10.1103/PhysRevLett.100.073003 | bibcode=2008PhRvL.100g3003M
 | pmid=18352546 | arxiv = 0708.1060| s2cid = 1357534
}}</ref>

The distribution of the electrons in solid materials can be visualized by [[angle-resolved photoemission spectroscopy]] (ARPES). This technique employs the photoelectric effect to measure the [[Reciprocal lattice|reciprocal space]]—a mathematical representation of periodic structures that is used to infer the original structure. ARPES can be used to determine the direction, speed and scattering of electrons within the material.<ref>
{{cite journal
 | last = Damascelli | first = A.
 | year = 2004
 | title = Probing the Electronic Structure of Complex Systems by ARPES
 | journal = [[Physica Scripta]]
 | volume = T109 | pages = 61–74
 | doi =10.1238/Physica.Topical.109a00061
 | arxiv = cond-mat/0307085 |bibcode = 2004PhST..109...61D | s2cid = 21730523
}}</ref>

== Plasma applications ==

=== Particle beams ===
[[File:Nasa Shuttle Test Using Electron Beam full.jpg|right|thumb|alt=A violet beam from above produces a blue glow about a Space shuttle model|During a [[NASA]] [[wind tunnel]] test, a model of the [[Space Shuttle]] is targeted by a beam of electrons, simulating the effect of [[ion]]izing gases during [[Atmospheric entry|re-entry]].<ref>
{{cite web
 |title=Image # L-1975-02972
 |department=[[Langley Research Center]]
 |publisher= [[NASA]] |date=April 4, 1975
 |url=https://grin.hq.nasa.gov/ABSTRACTS/GPN-2000-003012.html
 |url-status=dead |access-date=2008-09-20 |df=dmy-all
 |archive-url=https://web.archive.org/web/20081207041522/https://grin.hq.nasa.gov/ABSTRACTS/GPN-2000-003012.html
 |archive-date=December 7, 2008
}}</ref>]]

[[Cathode ray|Electron beams]] are used in [[electron beam welding|welding]].<ref>
{{cite web
 | last = Elmer | first = J.
 | title = Standardizing the Art of Electron-Beam Welding
 | publisher=[[Lawrence Livermore National Laboratory]]
 | date=March 3, 2008
 | url = https://www.llnl.gov/str/MarApr08/elmer.html
 |url-status=dead | access-date = 2008-10-16 |df=dmy-all
 | archive-url=https://web.archive.org/web/20080920142328/https://www.llnl.gov/str/MarApr08/elmer.html
 |archive-date=2008-09-20
}}</ref> They allow energy densities up to {{val|e=7|u=W·cm<sup>−2</sup>}} across a narrow focus diameter of {{nowrap|0.1–1.3 mm}} and usually require no filler material. This welding technique must be performed in a vacuum to prevent the electrons from interacting with the gas before reaching their target, and it can be used to join conductive materials that would otherwise be considered unsuitable for welding.<ref>
{{cite book
 | last = Schultz
 | first = H.
 | title = Electron Beam Welding
 | pages = 2–3
 | publisher = [[Woodhead Publishing]]
 | year = 1993
 | isbn = 978-1-85573-050-2
 | url = https://books.google.com/books?id=I0xMo28DwcIC&pg=PA2
 | access-date = 2020-08-25
 | archive-date = 2022-02-04
 | archive-url = https://web.archive.org/web/20220204084011/https://books.google.com/books?id=I0xMo28DwcIC&pg=PA2
 | url-status = live
}}</ref><ref>
{{cite book
 | last = Benedict
 | first = G.F.
 | title = Nontraditional Manufacturing Processes
 | series = Manufacturing engineering and materials processing
 | volume = 19
 | page = 273
 | publisher = [[CRC Press]]
 | year = 1987
 | isbn = 978-0-8247-7352-6
 | url = https://books.google.com/books?id=xdmNVSio8jUC&pg=PA273
 | access-date = 2020-08-25
 | archive-date = 2022-02-04
 | archive-url = https://web.archive.org/web/20220204084012/https://books.google.com/books?id=xdmNVSio8jUC&pg=PA273
 | url-status = live
}}</ref>

[[Electron-beam lithography]] (EBL) is a method of etching semiconductors at resolutions smaller than a [[Micrometre|micrometer]].<ref>
{{cite conference
 | last = Ozdemir | first = F.S.
 | title = Electron beam lithography | pages = 383–391
 | conference = Proceedings of the 16th Conference on Design automation
 | date = June 25–27, 1979 | place = San Diego, CA
 | publisher = [[IEEE Press]]
 | url = https://portal.acm.org/citation.cfm?id=800292.811744
 | access-date = 2008-10-16 |df=dmy-all
}}</ref> This technique is limited by high costs, slow performance, the need to operate the beam in the vacuum and the tendency of the electrons to scatter in solids. The last problem limits the resolution to about 10&nbsp;nm. For this reason, EBL is primarily used for the production of small numbers of specialized [[integrated circuit]]s.<ref>
{{cite book
 | last = Madou
 | first = M.J.
 | title = Fundamentals of Microfabrication: the Science of Miniaturization
 | pages = 53–54
 | publisher = CRC Press
 | edition = 2nd
 | year = 2002
 | isbn = 978-0-8493-0826-0
 | url = https://books.google.com/books?id=9bk3gJeQKBYC&pg=PA53
 | access-date = 2020-08-25
 | archive-date = 2021-01-07
 | archive-url = https://web.archive.org/web/20210107160805/https://books.google.com/books?id=9bk3gJeQKBYC&pg=PA53
 | url-status = live
}}</ref>

[[Electron beam processing]] is used to irradiate materials in order to change their physical properties or [[Sterilization (microbiology)|sterilize]] medical and food products.<ref>
{{cite conference
 | last1 = Jongen | first1 = Y.
 | last2 = Herer | first2 = A.
 | title=[no title cited]
 | conference = Electron Beam Scanning in Industrial Applications
 | department = APS/AAPT Joint Meeting
 | date =2–5 May 1996
 | publisher = [[American Physical Society]]
 | bibcode =1996APS..MAY.H9902J
}}</ref> Electron beams fluidise or quasi-melt glasses without significant increase of temperature on intensive irradiation: e.g. intensive electron radiation causes a many orders of magnitude decrease of viscosity and stepwise decrease of its activation energy.<ref>
{{cite journal
 | last1 = Mobus | first1 = G. | display-authors = etal
 | year = 2010
 | title =  Nano-scale quasi-melting of alkali-borosilicate glasses under electron irradiatio
 | journal = Journal of Nuclear Materials
 | volume = 396 | issue = 2–3 | pages = 264–271
 | doi = 10.1016/j.jnucmat.2009.11.020
 | bibcode = 2010JNuM..396..264M
}}</ref>

[[Linear particle accelerator]]s generate electron beams for treatment of superficial tumors in [[radiation therapy]]. [[Electron therapy]] can treat such skin lesions as [[basal-cell carcinoma]]s because an electron beam only penetrates to a limited depth before being absorbed, typically up to 5&nbsp;cm for electron energies in the range 5–20&nbsp;MeV. An electron beam can be used to supplement the treatment of areas that have been irradiated by [[X-ray]]s.<ref>
{{cite journal
 | last1 = Beddar | first1 = A.S.
 | last2 = Domanovic | first2 = Mary Ann
 | last3 = Kubu | first3 = Mary Lou
 | last4 = Ellis | first4 = Rod J.
 | last5 = Sibata | first5 = Claudio H.
 | last6 = Kinsella | first6 = Timothy J.
 | title = Mobile linear accelerators for intraoperative radiation therapy
 | journal = [[AORN Journal]] | year = 2001
 | volume = 74 | issue = 5 | pages = 700–705
 | doi =10.1016/S0001-2092(06)61769-9
 | pmid = 11725448
}}</ref><ref>
{{cite web
 | last1 = Gazda
 | first1 = M.J.
 | last2 = Coia
 | first2 = L.R.
 | date = June 1, 2007
 | title = Principles of Radiation Therapy
 | url = https://www.thymic.org/uploads/reference_sub/02radtherapy.pdf
 | access-date = 2013-10-31
 | df = dmy-all
 | archive-date = 2013-11-02
 | archive-url = https://web.archive.org/web/20131102114151/http://www.thymic.org/uploads/reference_sub/02radtherapy.pdf
 | url-status = live
}}</ref>

[[Particle accelerator]]s use electric fields to propel electrons and their antiparticles to high energies.  These particles emit synchrotron radiation as they pass through magnetic fields. The dependency of the intensity of this radiation upon spin polarizes the electron beam—a process known as the [[Sokolov–Ternov effect]].{{efn|The polarization of an electron beam means that the spins of all electrons point into one direction. In other words, the projections of the spins of all electrons onto their momentum vector have the same sign.}} Polarized electron beams can be useful for various experiments. [[Synchrotron]] radiation can also [[Radiation damping|cool]] the electron beams to reduce the momentum spread of the particles.  Electron and positron beams are collided upon the particles' accelerating to the required energies; [[particle detector]]s observe the resulting energy emissions, which [[particle physics]] studies.<ref>
{{cite book
 | last1 = Chao
 | first1 = A.W.
 | last2 = Tigner
 | first2 = M.
 | title = Handbook of Accelerator Physics and Engineering
 | pages = 155, 188
 | url = https://books.google.com/books?id=Z3J4SjftF1YC&pg=PA155
 | publisher = [[World Scientific]]
 | year = 1999
 | isbn = 978-981-02-3500-0
 | access-date = 2020-08-25
 | archive-date = 2022-02-04
 | archive-url = https://web.archive.org/web/20220204071146/https://books.google.com/books?id=Z3J4SjftF1YC&pg=PA155
 | url-status = live
}}</ref>

=== Imaging ===
[[Low-energy electron diffraction]] (LEED) is a method of bombarding a crystalline material with a [[Collimated light|collimated beam]] of electrons and then observing the resulting diffraction patterns to determine the structure of the material. The required energy of the electrons is typically in the range 20–200&nbsp;eV.<ref>
{{cite book
 | last = Oura | first = K.
 | title = Surface Science: An Introduction
 | pages = 1–45
 | publisher = [[Springer Science+Business Media]] | year = 2003
 | isbn = 978-3-540-00545-2
 |display-authors=etal
}}</ref> The [[reflection high-energy electron diffraction]] (RHEED) technique uses the reflection of a beam of electrons fired at various low angles to characterize the surface of crystalline materials. The beam energy is typically in the range 8–20&nbsp;keV and the angle of incidence is 1–4°.<ref>
{{cite book
 | last1 = Ichimiya
 | first1 = A.
 | last2 = Cohen
 | first2 = P.I.
 | title = Reflection High-energy Electron Diffraction
 | page = 1
 | publisher = Cambridge University Press
 | year = 2004
 | isbn = 978-0-521-45373-8
 | url = https://books.google.com/books?id=AUVbPerNxTcC&pg=PA1
 | access-date = 2020-08-25
 | archive-date = 2022-02-04
 | archive-url = https://web.archive.org/web/20220204084445/https://books.google.com/books?id=AUVbPerNxTcC&pg=PA1
 | url-status = live
}}</ref><ref>
{{cite journal
 | last = Heppell | first = T.A.
 | year = 1967
 | title = A combined low energy and reflection high energy electron diffraction apparatus
 | journal = [[Measurement Science and Technology|Journal of Scientific Instruments]]
 | volume = 44 | issue = 9 | pages = 686–688
 | doi =10.1088/0950-7671/44/9/311
 | bibcode = 1967JScI...44..686H
}}</ref>

The [[electron microscope]] directs a focused beam of electrons at a specimen. Some electrons change their properties, such as movement direction, angle, and relative phase and energy as the beam interacts with the material. Microscopists can record these changes in the electron beam to produce atomically resolved images of the material.<ref>
{{cite web
 | last = McMullan
 | first = D.
 | title = Scanning Electron Microscopy: 1928–1965
 | publisher = University of Cambridge
 | year = 1993
 | url = https://www-g.eng.cam.ac.uk/125/achievements/mcmullan/mcm.htm
 | access-date = 2009-03-23
 | df = dmy-all
 | archive-date = 2009-03-16
 | archive-url = https://web.archive.org/web/20090316071650/http://www-g.eng.cam.ac.uk/125/achievements/mcmullan/mcm.htm
 | url-status = live
}}</ref> In blue light, conventional [[optical microscope]]s have a diffraction-limited resolution of about 200&nbsp;nm.<ref>
{{cite book
 | last = Slayter
 | first = H.S.
 | title = Light and electron microscopy
 | page = 1
 | publisher = Cambridge University Press
 | year = 1992
 | isbn = 978-0-521-33948-3
 | url = https://books.google.com/books?id=LlePVS9oq7MC&pg=PA1
 | access-date = 2020-08-25
 | archive-date = 2022-02-04
 | archive-url = https://web.archive.org/web/20220204084446/https://books.google.com/books?id=LlePVS9oq7MC&pg=PA1
 | url-status = live
}}</ref> By comparison, electron microscopes are limited by the [[Matter wave|de Broglie wavelength]] of the electron. This wavelength, for example, is equal to 0.0037&nbsp;nm for electrons accelerated across a {{gaps|100|000}}-[[volt]] potential.<ref>
{{cite book
 | last = Cember
 | first = H.
 | title = Introduction to Health Physics
 | pages = 42–43
 | publisher = [[McGraw-Hill|McGraw-Hill Professional]]
 | year = 1996
 | isbn = 978-0-07-105461-4
 | url = https://books.google.com/books?id=obcmBZe9es4C&pg=PA42
 | access-date = 2020-08-25
 | archive-date = 2022-02-04
 | archive-url = https://web.archive.org/web/20220204084443/https://books.google.com/books?id=obcmBZe9es4C&pg=PA42
 | url-status = live
}}</ref> The [[Transmission Electron Aberration-Corrected Microscope]] is capable of sub-0.05&nbsp;nm resolution, which is more than enough to resolve individual atoms.<ref>
{{cite journal
 |last1           = Erni
 |first1          = R.
 |display-authors = etal
 |year            = 2009
 |title           = Atomic-Resolution Imaging with a Sub-50-pm Electron Probe
 |journal         = [[Physical Review Letters]]
 |volume          = 102
 |issue           = 9
 |page            = 096101
 |doi             = 10.1103/PhysRevLett.102.096101
 |bibcode         = 2009PhRvL.102i6101E
 |pmid            = 19392535
 |url             = https://digital.library.unt.edu/ark:/67531/metadc927376/
 |access-date     = 2018-08-17
 |archive-date    = 2020-01-02
 |archive-url     = https://web.archive.org/web/20200102164706/https://digital.library.unt.edu/ark:/67531/metadc927376/
 |url-status      = live
}}</ref> This capability makes the electron microscope a useful laboratory instrument for high resolution imaging. However, electron microscopes are expensive instruments that are costly to maintain.

Two main types of electron microscopes exist: [[Transmission electron microscopy|transmission]] and [[scanning electron microscope|scanning]]. Transmission electron microscopes function like [[overhead projector]]s, with a beam of electrons passing through a slice of material then being projected by lenses on a [[Reversal film|photographic slide]] or a [[charge-coupled device]].  Scanning electron microscopes [[Raster scan|rasteri]] a finely focused electron beam, as in a TV set, across the studied sample to produce the image. Magnifications range from 100× to {{gaps|1|000|000}}× or higher for both microscope types. The [[scanning tunneling microscope]] uses quantum tunneling of electrons from a sharp metal tip into the studied material and can produce atomically resolved images of its surface.<ref name="bozzola_1999">
{{cite book
 | last1 = Bozzola
 | first1 = J.J.
 | last2 = Russell
 | first2 = L.D.
 | title = Electron Microscopy: Principles and Techniques for Biologists
 | pages = 12, 197–199
 | publisher = [[Jones & Bartlett Learning|Jones & Bartlett Publishers]]
 | year = 1999
 | isbn = 978-0-7637-0192-5
 | url = https://books.google.com/books?id=RqSMzR-IXk0C&pg=PA12
 | access-date = 2020-08-25
 | archive-date = 2022-02-04
 | archive-url = https://web.archive.org/web/20220204084447/https://books.google.com/books?id=RqSMzR-IXk0C&pg=PA12
 | url-status = live
}}</ref><ref>
{{cite book
 | last1 = Flegler | first1 = S.L.
 | last2 = Heckman | first2 = J.W. Jr.
 | last3 = Klomparens | first3 = K.L.
 | title = Scanning and Transmission Electron Microscopy: An Introduction
 |publisher=Oxford University Press |edition=Reprint |year=1995
 | pages = 43–45
 | isbn = 978-0-19-510751-7
}}</ref><ref>
{{cite book
 | last1 = Bozzola
 | first1 = J.J.
 | last2 = Russell
 | first2 = L.D.
 | title = Electron Microscopy: Principles and Techniques for Biologists
 | page = 9
 | publisher = [[Jones & Bartlett Learning|Jones & Bartlett Publishers]]
 | edition = 2nd
 | year = 1999
 | isbn = 978-0-7637-0192-5
 | url = https://books.google.com/books?id=RqSMzR-IXk0C&pg=PA9
 | access-date = 2020-08-25
 | archive-date = 2022-02-04
 | archive-url = https://web.archive.org/web/20220204084444/https://books.google.com/books?id=RqSMzR-IXk0C&pg=PA9
 | url-status = live
}}</ref>

=== Other applications ===
In the [[free-electron laser]] (FEL), a [[relativistic electron beam]] passes through a pair of [[undulator]]s that contain arrays of [[dipole magnet]]s whose fields point in alternating directions. The electrons emit synchrotron radiation that [[Coherence (physics)|coherently]] interacts with the same electrons to strongly amplify the radiation field at the [[resonance]] frequency. FEL can emit a coherent high-[[Radiance|brilliance]] electromagnetic radiation with a wide range of frequencies, from [[microwave]]s to soft X-rays. These devices are used in manufacturing, communication, and in medical applications, such as soft tissue surgery.<ref>
{{cite book
 | last1 = Freund
 | first1 = H.P.
 | last2 = Antonsen
 | first2 = T.
 | title = Principles of Free-Electron Lasers
 | pages = 1–30
 | publisher = [[Springer Science+Business Media|Springer]]
 | year = 1996
 | isbn = 978-0-412-72540-1
 | url = https://books.google.com/books?id=73w9tqTgbiIC&pg=PA1
 | access-date = 2020-08-25
 | archive-date = 2022-02-04
 | archive-url = https://web.archive.org/web/20220204084620/https://books.google.com/books?id=73w9tqTgbiIC&pg=PA1
 | url-status = live
}}</ref>

Electrons are important in [[cathode-ray tube]]s, which have been extensively used as display devices in laboratory instruments, [[computer monitor]]s and [[television set]]s.<ref>
{{cite book
 | last = Kitzmiller | first = J.W.
 | title = Television Picture Tubes and Other Cathode-Ray Tubes: Industry and Trade Summary
 | pages = 3–5
 | publisher = Diane Publishing | year = 1995
 | isbn = 978-0-7881-2100-5
}}</ref> In a [[photomultiplier]] tube, every photon striking the [[photocathode]] initiates an avalanche of electrons that produces a detectable current pulse.<ref>
{{cite book
 | last = Sclater | first = N.
 | title = Electronic Technology Handbook
 | pages = 227–228
 | publisher = [[McGraw-Hill|McGraw-Hill Professional]] | year = 1999
 | isbn = 978-0-07-058048-0
}}</ref> [[Vacuum tube]]s use the flow of electrons to manipulate electrical signals, and they played a critical role in the development of electronics technology. However, they have been largely supplanted by [[Solid-state (electronics)|solid-state devices]] such as the [[transistor]].<ref>
{{cite web
 | title = The History of the Integrated Circuit
 | url = https://nobelprize.org/educational_games/physics/integrated_circuit/history/
 | publisher = [[Nobel Foundation|The Nobel Foundation]]
 | year = 2008
 | access-date = 2008-10-18
 | df = dmy-all
 | archive-date = 2008-12-01
 | archive-url = https://web.archive.org/web/20081201144536/http://nobelprize.org/educational_games/physics/integrated_circuit/history/
 | url-status = live
}}</ref>

== See also ==
{{Portal|Electronics|Physics|Science}}
{{cmn|colwidth=18em|
* [[Anyon]]
* [[Beta radiation]]
* [[Electride]]
* [[Electron bubble]]
* [[Exoelectron emission]]
* [[G-factor (physics)|''g''-factor]]
* [[Lepton]]
* [[List of particles]]
* [[One-electron universe]]
* [[Periodic systems of small molecules]]
* [[Spintronics]]
* [[Stern–Gerlach experiment]]
* [[Townsend discharge]]
* [[Zeeman effect]]
* [[Positron]] or antielectron is a antiparticle or antimatter counter part of the electron
}}

== Notes ==
{{notelist|25em}}

== References ==
{{reflist|25em|refs=

<ref name="anastopoulos1">{{cite book
 | last = Anastopoulos
 | first = C.
 | title = Particle Or Wave: The Evolution of the Concept of Matter in Modern Physics
 | pages = 236–237
 | publisher = Princeton University Press
 | year = 2008
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 | url = https://books.google.com/books?id=rDEvQZhpltEC&pg=PA236
 | access-date = 2020-08-25
 | archive-date = 2014-09-28
 | archive-url = https://web.archive.org/web/20140928082921/http://books.google.com/books?id=rDEvQZhpltEC&pg=PA236
 | url-status = live
}}</ref>

<ref name="DictOrigins">{{cite book
 | last = Shipley | first = J.T.
 | title = Dictionary of Word Origins
 | page = 133
 | publisher = [[The Philosophical Library]] | year = 1945
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 | url-access = registration
}}</ref>

<ref name="buchwald1">{{cite book
 | last1 = Buchwald
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 | last2 = Warwick
 | first2 = A.
 | title = Histories of the Electron: The Birth of Microphysics
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 | publisher = [[MIT Press]]
 | year = 2001
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 | ref = refBaW2001
 | access-date = 2020-08-25
 | archive-date = 2021-01-26
 | archive-url = https://web.archive.org/web/20210126182003/https://books.google.com/books?id=1yqqhlIdCOoC&pg=PA195
 | url-status = live
}}</ref>

<ref name=Gupta2001>{{cite book
 | last = Gupta
 | first = M.C.
 | year = 2001
 | title = Atomic and Molecular Spectroscopy
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 | archive-url = https://web.archive.org/web/20140930054250/http://books.google.com/books?id=0tIA1M6DiQIC&pg=PA81
 | url-status = live
}}</ref>

<ref name=HakenWolfBrewer2005>{{cite book
 |last1        = Haken
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 |last3        = Brewer
 |first3       = W.D.
 |year         = 2005
 |title        = The Physics of Atoms and Quanta: Introduction to Experiments and Theory
 |url          = https://books.google.com/books?id=SPrAMy8glocC&pg=PA70
 |publisher    = [[Springer Science+Business Media|Springer]]
 |page         = 70
 |isbn         = 978-3-540-67274-6
 |access-date  = 2020-08-25
 |archive-date = 2021-05-10
 |archive-url  = https://web.archive.org/web/20210510144005/https://books.google.com/books?id=SPrAMy8glocC&pg=PA70
 |url-status   = live
}}</ref>

<ref name=thomson>{{cite journal
 | last = Thomson
 | first = J.J.
 | year = 1897
 | title = Cathode Rays
 | journal = [[Philosophical Magazine]]
 | volume = 44
 | issue = 269
 | pages = 293–316
 | doi = 10.1080/14786449708621070
 | url = https://web.lemoyne.edu/~GIUNTA/thomson1897.html
 | access-date = 2022-02-24
 | archive-date = 2022-01-25
 | archive-url = https://web.archive.org/web/20220125001603/https://web.lemoyne.edu/~giunta/thomson1897.html
 | url-status = live
}}</ref>

<!--<ref name=CODATA2018>{{cite web
 |first1=P.J. |last1=Mohr
 |first2=B.N. |last2=Taylor
 |first3=D.B. |last3=Newell
 |title=2018 CODATA recommended values
 |others=This database was developed by J. Baker, M. Douma, and S. Kotochigova.
 |department=National Institute of Standards and Technology
 |publisher=U.S. Department of Commerce
 |place=Gaithersburg, MD
 |url=https://physics.nist.gov/cuu/Constants/index.html
 |access-date=2019-12-03 |url-status=live
 |archive-url=https://web.archive.org/web/20180122130230/https://physics.nist.gov/cuu/Constants/index.html
 |archive-date=2018-01-22
}}
</ref>-->

}}

== External links ==
{{Wikiquote}}
{{EB1911 poster|Electron}}
{{Commons category|Electrons}}
* {{cite web
 |title=The Discovery of the Electron
 |publisher=[[American Institute of Physics]]
 |department=Center for History of Physics
 |url=https://history.aip.org/exhibits/electron/
}}
* {{cite web
 | title = Particle Data Group
 | publisher = University of California
 | url = https://pdg.lbl.gov/
}}
* {{cite book
 | last1 = Bock | first1 = R.K.
 | last2 = Vasilescu | first2 = A.
 | title = The Particle Detector BriefBook
 | publisher = Springer | edition = 14th | year = 1998
 | isbn = 978-3-540-64120-9
 | url = https://physics.web.cern.ch/ParticleDetector/BriefBook/
}}

{{Authority control}}
{{Particles}}
{{Quantum field theories}}
{{Quantum gravity}}
{{Quantum electrodynamics}}
{{Quantum information}}
{{Radiation oncology}}
{{Featured article}}

[[Category:Electron| ]]
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