History of atomic theory: Difference between revisions
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{{dablink|For atomic theories in [[model theory]], see [[atomic model]].}} |
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''This article focuses on the historical models of the atom. For a history of the study of how atoms combine to form molecules, see [[History of the molecule]].'' |
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In [[chemistry]] and [[physics]], '''atomic theory''' is a [[theory]] of the nature of [[matter]], which states that matter is composed of discrete units called [[atom]]s, as opposed to the obsolete notion that matter could be divided into any arbitrarily small quantity. It began as a philosophical concept in ancient Greece and India and entered the scientific mainstream in the early 19th century when discoveries in the field of chemistry showed that matter did indeed behave as if it were made up of particles. |
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The name "atom" (from the Greek word ''atoma'', which means "indivisible"<ref>{{cite web|url=http://www.merriam-webster.com/dictionary/atoms|title=Atom|publisher=Merriam-Webster Online Dictionary|accessdate=2008-02-10}}</ref>) was attributed to the basic particle that constituted a chemical element, because the chemists of the era believed that these were the fundamental particles of matter. However, around the turn of the 20th century, through various experiments with [[electromagnetism]] and [[radioactivity]], physicists discovered that the so-called "indivisible atom" was actually a conglomerate of various subatomic particles (chiefly, [[electrons]], [[protons]] and [[neutrons]]) which can exist separately from each other. In fact, in certain extreme environments such as [[neutron stars]], extreme temperature and pressure prevents atoms from existing at all. The field of science which studies subatomic particles is [[particle physics]], and it is in this field that physicists hope to discover the true fundamental nature of matter. |
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==Philosophical atomism== |
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{{Main|Atomism}} |
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The concept that matter is composed of discrete units and cannot be divided into any arbitrarily small quantities has been around for thousands of years, but these ideas were founded in abstract, philosophical reasoning rather than scientific experimentation. The nature of atoms in philosophy varied considerably over time and between cultures and schools, and often had spiritual elements. Nevertheless, the basic idea of the atom was adopted by scientists thousands of years later because it could elegantly explain new discoveries in the field of chemistry. |
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===Indian=== |
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Some of the earliest known theories were developed in [[ancient India]] in the 6th century BCE by [[Kanada]], a [[Hindu]] philosopher.<ref name="lost">{{cite book | title = Lost Discoveries: The Ancient Roots of Modern Science | author = Teresi, Dick | publisher = Simon & Schuster | year = 2003 | isbn = 074324379X | url = http://books.google.com/books?id=pheL_ubbXD0C&dq | pages = 213–214}}</ref> In Hindu philosophy, the [[Nyaya]] and [[Vaisheshika]] schools developed elaborate theories on how atoms combined into more complex objects (first in pairs, then trios of pairs),<ref name="lost">{{cite book | title = Lost Discoveries: The Ancient Roots of Modern Science | author = Teresi, Dick | publisher = Simon & Schuster | year = 2003 | isbn = 074324379X | url = http://books.google.com/books?id=pheL_ubbXD0C&dq | pages = 213–214}}</ref> but believed the interactions were ultimately driven by the will of God (specifically, the Hindu [[Ishvara]]), and that the atoms themselves were otherwise inactive, without physical properties of their own{{Fact|date=November 2007}}. By contrast, [[Jaina|Jainic]] philosophy linked the behavior of matter to the nature of the atoms themselves. Each atom, according to Jaina philosophy, has one kind of taste, one smell, one color, and two kinds of touch, though it is unclear what was meant by “kind of touch”. Atoms can exist in one of two states: subtle, in which case they can fit in infinitesimally small spaces, and gross, in which case they have extension and occupy a finite space. Although atoms are made of the same basic substance, they can combine based on their eternal properties to produce any of six “aggregates,” which seem to correspond with the Greek concept of “elements”: earth, water, shadow, sense objects, karmic matter, and unfit matter.<ref name="Gangopadhyaya">Gangopadhyaya, Mrinalkanti. ''Indian Atomism: History and Sources''. Atlantic Highlands, New Jersey: Humanities Press, 1981. ISBN 0-391-02177-X</ref> |
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===Greek=== |
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In the 5th century BCE, [[Democritus]] developed the concept of atoms in order to reconcile two conflicting schools of thought on the nature of reality. On one side was [[Heraclitus]], who believed that the nature of all existence is change. On the other side was [[Parmenides]], who believed instead that all change is illusion. |
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Parmenides denied the existence of motion, change and void. He believed all existence to be a single, all-encompassing and unchanging mass (a concept known as [[monism]]), and that change and motion were mere illusions. This conclusion, as well as the reasoning that lead to it, may indeed seem baffling to the modern empirical mind, but Parmenides explicitly rejected sensory experience as the path to an understanding of the universe, and instead used purely abstract reasoning. Firstly, he believed there is no such thing as void, equating it with non-being (ie "if the void '''''is''''', then it is not nothing; therefore it is not the void"). This in turn meant that motion is impossible, because there is no void to move into.<ref name="History of Western Philosophy">Bertrand Russel. (1946). ''History of Western Philosophy''. pg 75. ISBN 0-415-32505-6</ref> He also wrote all that '''''is''''' must be an indivisible unity, for if it were manifold, then there would have to be a void that could divide it (and he did not believe the void exists). Finally, he stated that the all encompassing Unity is unchanging, for the Unity already encompasses all that is and can be. |
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Democritus accepted most of Parmenides' arguments, except for the idea that change is an illusion. He believed change was real, and if it was not then at least the illusion had to be explained. He thus supported the concept of void, and stated that the universe is made up of multiple indivisble Parmenidean entities that move around in the void. These entities, which '''''are''''', are indeed unchangeable and indivisible ("atomos", the Greek word for uncuttable), but their arrangement in space is constantly changing. Democritus's atoms were made of the same material but had a limitless variety of shapes and sizes; this, coupled with their arrangement in space, explained all the different substances and objects in the universe.<ref name="From Atomos to Atom">Andre G. van Melsen. (1952) ''From Atomos to Atom''. ISBN 0-486-49584-1</ref> |
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===Islamic=== |
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In the 11th century, during the [[Islamic Golden Age]], [[Early Islamic philosophy|early Islamic philosophers]] developed atomic theories that represent a synthesis of both Greek and Indian [[atomism]]. Older Greek and Indian ideas were further developed by Islamic atomists, along with new Islamic ideas, such as the possibility of there being particles smaller than an atom. The most successful form of Islamic atomism was in the [[Ash'ari|Asharite]] school of [[Kalam|Islamic theology]], most notably in the work of the theologian [[Al-Ghazali]] (1058-1111). In Asharite atomism, atoms are the only perpetual, material things in existence, and all else in the world is “accidental” meaning something that lasts for only an instant. Nothing accidental can be the cause of anything else, except perception, as it exists for a moment. Contingent events are not subject to natural physical causes, but are the direct result of God’s constant intervention, without which nothing could happen. Thus nature is completely dependent on God, which meshes with other Asharite Islamic ideas on [[Causality|causation]], or the lack thereof.<ref name="Gardet">L. Gardet (2001), “djuz’”, in ''Encyclopaedia of Islam'', CD-ROM Edition, v. 1.1, Leiden: Brill</ref> |
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==Modern atomic theory== |
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===Birth=== |
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[[Image:A New System of Chemical Philosophy fp.jpg|right|thumb|Various atoms and molecules as depicted in [[John Dalton|John Dalton's]] ''A New System of Chemical Philosophy'' (1808).]] |
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In the early years of the 19th century, [[John Dalton]] developed his atomic theory in which he proposed that each chemical element is composed of atoms of a single, unique type, and that though they are both immutable and indestructible, they can combine to form more complex structures ([[chemical compound]]s). How precisely Dalton arrived at his theory is not entirely clear, but nonetheless it allowed him to explain various new discoveries in chemistry that he and his contemporaries made. |
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The first was the [[conservation of mass|law of conservation of mass]], formulated by [[Antoine Lavoisier]] in 1789, which states that the total mass in a chemical reaction remains constant (that is, the reactants have the same mass as the products).<ref name="Lavoisier">Weisstein, Eric W. "[http://scienceworld.wolfram.com/biography/Lavoisier.html Lavoisier, Antoine (1743-1794)]." ''scienceworld.wolfram.com.'' Retrieved on [[August 29]], [[2007]].</ref> This law suggested to Dalton that matter is fundamentally indestructible. |
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The second was the [[law of definite proportions]]. First proven by the French chemist [[Joseph Louis Proust]] in 1799,<ref name="proust">Proust, Joseph Louis. "[http://web.lemoyne.edu/~GIUNTA/proust.html Researches on Copper]", excerpted from ''Ann. chim.'' 32, 26-54 (1799) [as translated and reproduced in Henry M. Leicester and Herbert S. Klickstein, A Source Book in Chemistry, 1400-1900 (Cambridge, MA: Harvard, 1952)]. Retrieved on [[August 29]], [[2007]].</ref> this law states that if a compound is broken down into its constituent elements, then the masses of the constituents will always have the same proportions, regardless of the quantity or source of the original substance. Proust had synthesized [[copper carbonate]] through numerous methods and found that in each case the ingredients combined in the same proportions as they were produced when he broke down natural copper carbonate. |
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Dalton studied and expanded upon Proust's work to develop the [[law of multiple proportions]]: if two elements form more than one compound between them, then the ratios of the masses of the second element which combine with a fixed mass of the first element will be ratios of small [[integers]]. One pair of reactions Dalton studied involved the combinations of "nitrous air", or what we now call [[nitric oxide]] (NO), and [[oxygen]] (O<sub>2</sub>). Under certain conditions, these gases formed an unknown product at a certain combining ratio (now known to be [[nitrogen dioxide]] (NO<sub>2</sub>)), but when he repeated the reaction under other conditions, exactly twice the amount of nitric oxide (a ratio of 1:2 -- small integers) reacted completely with oxygen to form a different product -- now known as [[dinitrogen trioxide]] (N<sub>2</sub>O<sub>3</sub>). |
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2NO + O<sub>2</sub> → 2NO<sub>2</sub> |
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4NO + O<sub>2</sub> → 2N<sub>2</sub>O<sub>3</sub> |
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Dalton also believed atomic theory could explain why water absorbed different gases in different proportions: for example, he found that water absorbed [[carbon dioxide]] far better than it absorbed [[nitrogen]]. Dalton hypothesized this was due to the differences in mass and complexity of the gases' respective particles. Indeed, carbon dioxide molecules (CO<sub>2</sub>) are heavier and larger than nitrogen molecules (N<sub>2</sub>). |
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In 1803 Dalton orally presented his first list of relative atomic weights for a number of substances. This paper was published in 1805, but he did not discuss there exactly how he obtained these figures.<ref name = "Dalton_1803_paper">Dalton, John. "[http://web.lemoyne.edu/~GIUNTA/dalton52.html On the Absorption of Gases by Water and Other Liquids]", in ''Memoirs of the Literary and Philosophical Society of Manchester''. 1803. Retrieved on [[August 29]], [[2007]].</ref> The method was first revealed in 1807 by his acquaintance [[Thomas Thomson]], in the third edition of Thomson's textbook, ''A System of Chemistry''. Finally, Dalton published a full account in his own textbook, ''A New System of Chemical Philosophy'', 1808 and 1810. |
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Dalton estimated the atomic weights according to the mass ratios in which they combined, with hydrogen being the basic unit. However, Dalton did not conceive that with some elements atoms exist in molecules – e.g. pure oxygen exists as O<sub>2</sub>. He also mistakenly believed that the simplest compound between any two elements is always one atom of each (so he thought water was HO, not H<sub>2</sub>O).<ref>Johnson, Chris. "[http://www.bulldog.u-net.com/avogadro/avoga.html Avogadro - his contribution to chemistry]." Last modified on [[July 4]], [[2004]]. Retrieved on [[August 29]], [[2007]].</ref> This, in addition to the crudity of his equipment, resulted in his table being highly flawed. For instance, he believed oxygen atoms were 5.5 times heavier than hydrogen atoms, because in water he measured 5.5 grams of oxygen for every 1 gram of hydrogen and believed the formula for water was HO (an oxygen atom is actually 16 times heavier than a hydrogen atom). |
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The flaw in Dalton's theory was corrected in 1811 by [[Amedeo Avogadro]]. Avogadro had proposed that equal volumes of any two gases, at equal temperature and pressure, contain equal numbers of molecules (in other words, the mass of a gas's particles does not affect its volume).<ref name="avogadro">Avogadro, Amedeo. "[http://web.lemoyne.edu/~giunta/avogadro.html Essay on a Manner of Determining the Relative Masses of the Elementary Molecules of Bodies, and the Proportions in Which They Enter into These Compounds]." 1811. ''Journal de Physique'', 73, 58-76. Retrieved on [[August 29]], [[2007]].</ref> [[Avogadro's law]] allowed him to deduce the diatomic nature of numerous gases by studying the volumes at which they reacted. For instance: since two liters of hydrogen will react with just one liter of oxygen to produce two liters of water vapor (at constant pressure and temperature), it meant a single oxygen molecule splits in two in order to form two particles of water. Thus, Avogadro was able to offer more accurate estimates of the atomic mass of oxygen and various other elements, and firmly established the distinction between molecules and atoms. |
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In 1827, the British botanist [[Robert Brown (botanist)|Robert Brown]] observed that pollen particles floating in water constantly jiggled about for no apparent reason. In 1905, [[Albert Einstein]] theorized that this [[Brownian motion]] was caused by the water molecules continuously knocking the grains about, and developed a hypothetical mathematical model to describe it.<ref name="einstein">Einstein, Albert. "[http://lorentz.phl.jhu.edu/AnnusMirabilis/AeReserveArticles/eins_brownian.pdf On the Movement of Small Particles Suspended in Stationary Liquids Required by the Molecular-Kinetic Theory of Heat]." ''Annal der Physik''. Retrieved on [[August 29]], [[2007]].</ref> This model was validated experimentally in 1908 by French physicist [[Jean Perrin]], thus providing additional validation for particle theory (and by extension atomic theory). |
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===Discovery of subatomic particles=== |
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[[Image:JJ Thomson exp2.jpg|right|300px|thumb|[[J.J. Thomson|Thomson's]] [[Crookes tube]] in which he observed the deflection of [[cathode ray]]s by an [[electric field]]. The purple line represents the deflected electron stream.]] |
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Atoms were thought to be the smallest possible division of matter until 1897 when [[J.J. Thomson]] discovered the [[electron]] through his work on [[cathode ray]]s.<ref name="thomson">Thomson, J.J. "[http://web.lemoyne.edu/~GIUNTA/thomson1897.html Cathode rays]." ''Philosophical Magazine,'' 44, 293 (1897). [facsimile from Stephen Wright, Classical Scientific Papers, Physics (Mills and Boon, 1964).] Retrieved on [[August 29]], [[2007]].</ref> A [[Crookes tube]] is a sealed glass container in which two [[electrode]]s are separated by a [[vacuum]]. When a [[voltage]] is applied across the electrodes, cathode rays are generated, creating a glowing patch where they strike the glass at the opposite end of the tube. Through experimentation, Thomson discovered that the rays could be deflected by an [[electric field]] (in addition to [[magnetic field]]s, which was already known). He concluded that these rays, rather than being [[wave]]s, were composed of [[electric charge|negatively charged]] particles he called "corpuscles" (they would later be renamed electrons by other scientists). |
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Thomson believed that the corpuscles emerged from the very atoms of the electrode. He thus concluded that atoms were divisible, and that the corpuscles were their building blocks. To explain the overall neutral charge of the atom, he proposed that the corpuscles were distributed in a uniform sea or cloud of positive charge; this was the [[plum pudding model]].<ref name="thomson2">Thomson, J.J. "[http://dbhs.wvusd.k12.ca.us/webdocs/Chem-History/Thomson-Structure-Atom.html On the Structure of the Atom: an Investigation of the Stability and Periods of Oscillation of a number of Corpuscles arranged at equal intervals around the Circumference of a Circle; with Application of the Results to the Theory of Atomic Structure]." ''Philosophical Magazine'' March 1904. Series 6, Vol 7, No 39. Retrieved on [[August 29]], [[2007]].</ref> |
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Since atoms were found to be actually divisible, physicists later invented the term "[[elementary particle]]s" to describe indivisible particles. |
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===Discovery of the nucleus=== |
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[[Image:Gold foil exp conclusions.jpg|right|200px|thumb|'''The gold foil experiment'''<br> |
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''Top:'' Expected results: alpha particles passing through the plum pudding model of the atom with negligible deflection.<br> |
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''Bottom:'' Observed results: a small portion of the particles were deflected, indicating a small, concentrated positive charge.]] |
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Thomson's [[plum pudding model]] was disproved in 1909 by one of his students, [[Ernest Rutherford]], who discovered that most of the mass and positive charge of an atom is concentrated in a very small fraction of its volume, which he assumed to be at the very center. |
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In the [[Geiger-Marsden experiment|gold foil experiment]], [[Hans Geiger]] and [[Ernest Marsden]] (colleagues of Rutherford working at his behest) shot [[alpha particle]]s through a thin sheet of [[gold]], striking a [[fluorescence|fluorescent screen]] that surrounded the sheet.<ref name="geiger">Geiger, H. "[http://dbhs.wvusd.k12.ca.us/webdocs/Chem-History/Geiger-1910.html The Scattering of the α-Particles by Matter]." ''Proceedings of the Royal Society'' [[February 17]], [[1910]]. Series A 82: 495–500. Retrieved on [[August 29]], [[2007]].</ref> Given the very small mass of the electrons, the high [[momentum]] of the alpha particles and the unconcentrated distribution of positive charge of the plum pudding model, the experimenters expected all the alpha particles to either pass through without significant deflection or be absorbed. To their astonishment, a small fraction of the alpha particles experienced heavy deflection. This led Rutherford to propose the [[Rutherford model|planetary model]] of the atom in which pointlike electrons orbited in the space around a massive, compact [[atomic nucleus|nucleus]]—like [[planet]]s orbiting the [[Sun]].<ref name="rutherford">Rutherford, Ernest. "[http://dbhs.wvusd.k12.ca.us/webdocs/Chem-History/Rutherford-1911/Rutherford-1911.html The Scattering of α and β Particles by Matter and the Structure of the Atom]." ''Philosophical Magazine.'' May 1911. Series 6, Vol. 21. Retrieved on [[August 29]], [[2007]].</ref> |
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===Discovery of isotopes=== |
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While experimenting with the products of [[radioactive decay]], in 1913 [[radiochemistry|radiochemist]] [[Frederick Soddy]] discovered that there appeared to be more than one element at each position on the [[periodic table]].<ref>{{cite web |
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| url=http://nobelprize.org/nobel_prizes/chemistry/laureates/1921/soddy-bio.html |
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| title=Frederick Soddy, The Nobel Prize in Chemistry 1921 |
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| publisher=Nobel Foundation |
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| accessdate=2008-01-18 |
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}}</ref> The term [[isotope]] was coined by [[Margaret Todd (doctor)|Margaret Todd]] as a suitable name for these elements. |
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That same year, [[J.J. Thomson]] conducted an experiment in which he channeled a stream of [[neon]] [[ion]]s through magnetic and electric fields, striking a photographic plate at the other end. He observed two glowing patches on the plate, which suggested two different deflection trajectories. Thomson concluded this was because some of the neon ions had a different mass.<ref name="thompson3">Thomson, J.J. "[http://web.lemoyne.edu/~giunta/canal.html Rays of positive electricity]." ''Proceedings of the Royal Society.'' 1913. A 89, 1–20 [as excerpted in Henry A. Boorse & Lloyd Motz, ''The World of the Atom'', Vol. 1 (New York: Basic Books, 1966)]. Retrieved on [[August 29]], [[2007]].</ref> The nature of this differing mass would later be explained by the discovery of [[neutron]]s in 1932. |
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===Discovery of nuclear particles=== |
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{{seealso|Prout's hypothesis}} |
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In 1918, [[Ernest Rutherford|Rutherford]] bombarded [[nitrogen]] gas with [[alpha particle]]s and observed [[hydrogen]] nuclei being emitted from the gas. Rutherford concluded that the hydrogen nuclei emerged from the nuclei of the nitrogen atoms themselves (in effect, he split the atom).<ref>Rutherford, Ernest. "[http://web.lemoyne.edu/~GIUNTA/rutherford.html Collisions of alpha Particles with Light Atoms. IV. An Anomalous Effect in Nitrogen.]" ''Philosophical Magazine.'' 1919. 6th series, 37, 581. Retrieved on [[August 29]], [[2007]].</ref> He later found that the positive charge of any atom could always be equated to that of an integer number of hydrogen nuclei. This, coupled with the facts that hydrogen was the lightest element known and that the [[atomic mass]] of every other element was roughly equivalent to a whole multiple of hydrogen's atomic mass, led him to conclude hydrogen nuclei were singular particles and a basic constituent of all atomic nuclei: the [[proton]]. Further experimentation by Rutherford found that the nuclear mass of most atoms exceeded that of the protons it possessed; he speculated that this surplus mass was composed of hitherto unknown neutrally charged particles, which were tentatively dubbed "[[neutron]]s". |
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In 1928, [[Walter Bothe]] observed that [[beryllium]] emitted a highly penetrating, electrically neutral radiation when bombarded with alpha particles. It was later discovered that this radiation could knock hydrogen atoms out of [[paraffin wax]]. Initially it was thought to be high-energy [[gamma radiation]], since gamma radiation had a similar effect on electrons in metals, but [[James Chadwick]] found that the [[ionisation]] effect was too strong for it to be due to electromagnetic radiation. In 1932, he exposed various elements, such as hydrogen and nitrogen, to the mysterious "beryllium radiation", and by measuring the energies of the recoiling charged particles, he deduced that the radiation was actually composed of electrically neutral particles with a mass similar to that of a proton.<ref>Chadwick, James. (February 27, 1932), "[http://dbhs.wvusd.k12.ca.us/webdocs/Chem-History/Chadwick-neutron-letter.html Possible Existence of a Neutron]." ''Nature.'' [[February 27]], [[1932]]. p. 312. Retrieved on [[August 29]], [[2007]].</ref> For his discovery of the [[neutron]], Chadwick received the Nobel Prize in 1935. |
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===Quantum physical models of the atom=== |
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[[Image:Bohr atom model English.svg|thumb|right|The [[Bohr model]] of the atom]] |
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The planetary model of the atom had shortcomings. Firstly, according to the [[Larmor formula]] in [[classical electromagnetism]], an accelerating [[electric charge]] emits [[electromagnetic wave]]s; an orbiting charge would steadily lose energy and spiral towards the nucleus, colliding with it in a small fraction of a second. Another phenomenon the model did not explain was why excited atoms only emit light within certain [[emission spectrum|discrete spectra]]. |
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[[Quantum mechanics|Quantum theory]] revolutionized physics at the beginning of the 20th century, when [[Max Planck]] and [[Albert Einstein]] postulated that light energy is emitted or absorbed in discrete amounts known as [[Quantum|quanta]] (singular, ''quantum''). In 1913, [[Niels Bohr]] incorporated this idea into his [[Bohr model]] of the atom, in which the electrons could only orbit the nucleus in particular circular orbits with fixed [[angular momentum]] and energy, their distances from the nucleus (i.e., their radiuses) being proportional to their respective energies.<ref name="NBohr">Bohr, N. "[http://dbhs.wvusd.k12.ca.us/webdocs/Chem-History/Bohr/Bohr-1913a.html On the constitution of atoms and molecules]." ''Philosophical Magazine''. July 1913. 26, 1-25. Retrieved on [[August 29]], [[2007]].</ref> Under this model electrons could not spiral into the nucleus because they could not lose energy in a continuous manner; instead, they could only make instantaneous "[[quantum leap]]s" between the fixed [[energy level]]s.<ref name="NBohr"/> When this occurred, light was emitted or absorbed at a frequency proportional to the change in energy (hence the absorption and emission of light in discrete spectra).<ref name="NBohr"/> |
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Bohr's model was only able to predict the [[spectral line]]s of hydrogen; it couldn't predict those of multielectron atoms. Worse still, as [[Spectrophotometry|spectrographic]] technology improved, additional spectral lines in hydrogen were observed which Bohr's model couldn't explain. In 1916, [[Arnold Sommerfeld]] added elliptical orbits to the Bohr model to explain the extra emission lines, but this made the model very difficult to use, and it still couldn't explain complex atoms. |
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In 1924, [[Louis de Broglie]] proposed that all moving particles–particularly subatomic particles such as electrons–exhibit a degree of wave-like behavior. [[Erwin Schrödinger]], fascinated by this idea, explored whether or not the movement of an electron in an atom could be better explained as a wave rather than as a particle. [[Schrödinger's equation]], published in 1926,<ref name="schrodinger">Schrödinger, Erwin. "Quantisation as an Eigenvalue Problem." ''Annalen der Physik.''</ref> describes an electron as a [[wavefunction]] instead of as a point particle, and it elegantly predicted many of the spectral phenomena Bohr's model failed to explain. Although this concept was mathematically convenient, it was difficult to visualize, and faced opposition.<ref name="Mahanti">Mahanti, Subodh. "[http://www.vigyanprasar.gov.in/scientists/ESchrodinger.htm Erwin Schrödinger: The Founder of Quantum Wave Mechanics]." Retrieved on [[August 29]], [[2007]].</ref> One of its critics, [[Max Born]], proposed instead that Schrödinger's wavefunction described not the electron but rather all its possible states, and thus could be used to calculate the probability of finding an electron at any given location around the nucleus.<ref>Mahanti, Subodh. "[http://www.vigyanprasar.gov.in/scientists/MBorn.htm Max Born: Founder of Lattice Dynamics]." Retrieved on [[August 29]], [[2007]].</ref> |
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[[Image:neon orbitals.JPG|frame|right|The five atomic orbitals of a neon atom, separated and arranged in order of increasing energy from left to right, with the last three orbitals being [[Degenerate energy level|equal in energy]]. Each orbital holds up to two electrons, which exist for most of the time in the zones represented by the colored bubbles. Each electron is equally in both orbital zones, shown here by color only to highlight the different wave phase.]] |
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Since a wavefunction incorporates time as well as position, it is impossible to simultaneously derive precise values for both the position and momentum of a particle for any given point in time; this became known as the [[uncertainty principle]]. This invalidated Bohr's model, with its neat, clearly defined circular orbits. The modern model of the atom describes the positions of electrons in an atom in terms of probabilities. An electron can potentially be found at any distance from the nucleus, but—depending on its energy level—tends to exist more frequently in certain regions around the nucleus than others; this pattern is referred to as its [[atomic orbital]]. |
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==See also== |
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<div style="-moz-column-count:2; column-count:2;"> |
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*[[History of the molecule]] |
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*[[Discoveries of the chemical elements]] |
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*[[Introduction to quantum mechanics]] |
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*[[Kinetic theory]] |
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</div> |
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==Notes== |
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{{reflist|2}} |
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==External links== |
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*[http://plato.stanford.edu/entries/atomism-ancient/ Ancient Atomism] |
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*[http://www.chemcases.com/nuclear/nc-01.htm Discovery of the Neutron] |
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*[http://library.thinkquest.org/19662/low/eng/main.html Atom: The Incredible World] |
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[[Category:Atomic physics| ]] |
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[[Category:Statistical mechanics]] |
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[[Category:Chemistry theories]] |
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[[Category:Foundational quantum physics]] |
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[[Category:Amount of substance]] |
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[[ar:نظرية ذرية]] |
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[[bs:Atomska teorija]] |
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[[cs:Atomová teorie]] |
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[[es:Teoría atómica]] |
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[[fr:Théorie atomique]] |
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[[id:Teori atom]] |
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[[simple:Atomic theory]] |
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Revision as of 16:26, 30 September 2008
Amanda Allegrucci deleted all of this. Shes a meathead.