Ion

For other uses, see Ion (disambiguation).

An electrostatic potential map of the nitrate ion (NO₃⁻). Areas coloured red are lower in energy than areas colored yellow

A 'IONS' is an atom or molecule which has lost or gained one or more electrons, giving it a positive or negative electrical charge. According to the Model of Bohr this will be from or in the outer shield 'n'.

A negatively charged ion, which has more electrons than it has protons, is known as an anion (ἀνά ana: Greek 'up') (Template:PronEng; an-eye-on). Conversely, a positively-charged ion, which has fewer electrons than protons, is known as a cation (κατά kata: Greek 'down') (Template:PronEng; cat-eye-on).

An ion consisting of a single atom is called a monatomic ion, but if it consists of two or more atoms, it is a polyatomic ion. Polyatomic ions containing oxygen, such as carbonate and sulfate, are called oxyanions.

Ions are denoted in the same way as electrically neutral atoms and molecules except for the presence of a superscript indicating the sign of the net electric charge and the number of electrons lost or gained, if more than one. For example: H⁺ and SO₄²⁻.

Formation

Formation of polyatomic and molecular ions

Polyatomic and molecular ions are often formed by the combination of elemental ions such as H⁺ with neutral molecules or by the gain of such elemental ions from neutral molecules. A simple example of this is the ammonium ion NH₄⁺ which can be formed by ammonia NH₃ accepting a proton, H⁺. Ammonia and ammonium have the same number of electrons in essentially the same electronic configuration but differ in protons. The charge has been added by the addition of a proton (H⁺) not the addition or removal of electrons. The distinction between this and the removal of an electron from the whole molecule is important in large systems because it usually results in much more stable ions with complete electron shells. For example NH₃·⁺ is not stable because of an incomplete valence shell around nitrogen and is in fact a radical ion.

Ionization potential

Main article: Ionization potential

The energy required to detach an electron in its lowest energy state from an atom or molecule of a gas with less net electric charge is called the ionization potential, or ionization energy. The nth ionization energy of an atom is the energy required to detach its nth electron after the first n − 1 electrons have already been detached.

Each successive ionization energy is markedly greater than the last. Particularly great increases occur after any given block of atomic orbitals is exhausted of electrons. For this reason, ions tend to form in ways that leave them with full orbital blocks. For example, sodium has one valence electron, in its outermost shell, so in ionized form it is commonly found with one lost electron, as Na⁺. On the other side of the periodic table, chlorine has seven valence electrons, so in ionized form it is commonly found with one gained electron, as Cl⁻. Caesium has the lowest measured ionization energy of all the elements and helium has the greatest. The ionization energy of metals is generally much lower than the ionization energy of nonmetals, which is why metals will generally lose electrons to form positively-charged ions while nonmetals will generally gain electrons to form negatively-charged ions

A neutral atom contains an equal number of Z protons in the nucleus and Z electrons in the electron shell. The electrons' negative charges thus exactly cancel the protons' positive charges. In the simple view of the Free electron model, a passing electron is therefore not attracted to a neutral atom and cannot bind to it. In reality, however, the atomic electrons form a cloud into which the additional electron penetrates, thus being exposed to a net positive charge part of the time. Furthermore, the additional charge displaces the original electrons and all of the Z + 1 electrons rearrange into a new configuration.

Ions

• Anions are negatively charged ions, formed when an atom gains electrons in a reaction. Anions are negatively charged because there are more electrons associated with them than there are protons in their nuclei.

• Cations are positively charged ions, formed when an atom loses electrons in a reaction. Cations are the opposite of anions, since cations have fewer electrons than protons.

• Radicals or radical ions are atom groups that contain unpaired electrons and are highly reactive.

Ionic bonding

An ionic bond is a type of chemical bond that involves a metal and a non-metal ion (or polyatomic ions such as ammonium) through electrostatic attraction. In short, it is a bond formed by the attraction between two oppositely charged ions.

The metal donates one or more electrons, forming a positively charged ion or cation with a stable electron configuration. These electrons then enter the non metal, causing it to form a negatively charged ion or anion which also has a stable electron configuration. The electrostatic attraction between the oppositely charged ions causes them to come together and form a bond.

For example, common table salt is sodium chloride. When sodium (Na) and chlorine (Cl) are combined, the sodium atoms each lose an electron, forming a cation (Na+), and the chlorine atoms each gain an electron to form an anion (Cl-). These ions are then attracted to each other in a 1:1 ratio to form sodium chloride (NaCl).

Na + Cl → Na+ + Cl− → NaCl

Electron configurations of lithium and fluorine. Lithium has one electron in its outer shell, held rather loosely because the ionization energy is low. Fluorine carries 7 electrons in its outer shell. When one electron moves from lithium to fluorine, each ion acquires the noble gas configuration. The bonding energy from the electrostatic attraction of the two oppositely-charged ions has a large enough negative value that the overall bonded state energy is lower than the unbonded stateThe removal of electrons from the atoms is endothermic and causes the ions to have a higher energy. There may also be energy changes associated with breaking of existing bonds or the addition of more than one electron to form anions. However, the attraction of the ions to each other lowers their energy.

Ionic bonding will occur only if the overall energy change for the reaction is favourable – when the bonded atoms have a lower energy than the free ones. The larger the resulting energy change the stronger the bond. The low electronegativity of metals and high electronegativity of non-metals means that the energy change of the reaction is most favorable when metals lose electrons and non-metals gain electrons. An ionic bond doesn't need metal.

Pure ionic bonding is not known to exist. All ionic compounds have a degree of covalent bonding. The larger the difference in electronegativity between two atoms, the more ionic the bond. Ionic compounds conduct electricity when molten or in solution. They generally have a high melting point and tend to be soluble in water.

New thinking on ionic bonding

In March 2009, a team of scientists from the University of Dallas shocked the scientific world when they discovered that in order for the electrons to be displaced from their original molecule; a free roaming neutron must collide with an electron from the outer shell. This process results in the electron being pushed from one atom to the other, thus forming the separate ions.

Plasma

Main article: Plasma (physics)

A collection of non-aqueous gas-like ions, or even a gas containing a proportion of charged particles, is called a plasma, often called the fourth state of matter because its properties are quite different from solids, liquids, and gases. Astrophysical plasmas containing predominantly a mixture of electrons and protons, may make up as much as 99.9% of visible matter in the universe.

Applications

Ions are essential to life. Sodium, potassium, calcium and other ions play an important role in the cells of living organisms, particularly in cell membranes. They have many practical, everyday applications in items such as smoke detectors, and are also finding use in unconventional technologies such as ion engines. Inorganic dissolved ions are a component of total dissolved solids, an indicator of water quality in the world.

Common ions

Common Cations Common Name Formula Historic Name Simple Cations Aluminium Al3+ alumen Barium Ba2+ Baryta Beryllium Be2+ beryl Cadmium Cd2+ cadmia Caesium Cs+ caesius Calcium Ca2+ calx Chromium(II) Cr2+ Chromous Chromium(III) Cr3+ Chromic Chromium(VI) Cr6+ Chromyl Cobalt(II) Co2+ Cobaltous Cobalt(III) Co3+ Cobaltic Copper(I) Cu+ Cuprous Copper(II) Cu2+ Cupric Copper(III) Cu3+ cuprum Gallium Ga3+ Gallia Gold (I) Au+ Gold (III) Au3+ Helium He2+ (Alpha particle) Hydrogen H+ (Proton) Iron(II) Fe2+ Ferrous Iron(III) Fe3+ Ferric Lead(II) Pb2+ Plumbous Lead(IV) Pb4+ Plumbic Lithium Li+ lithos Magnesium Mg2+ Magnesia Manganese(II) Mn2+ Manganous Manganese(III) Mn3+ Manganic Manganese(IV) Mn4+ Manganese(VII) Mn7+ Mercury(II) Hg2+ Mercuric Nickel(II) Ni2+ Nickelous Nickel(III) Ni3+ Nickelic Potassium K+ potash Silver Ag+ siolfur Sodium Na+ soda Strontium Sr2+ Strontian Thallium (I) Tl+ Thallium (III) Tl3+ Tin(II) Sn2+ Stannous Tin(IV) Sn4+ Stannic Zinc Zn2+ zink Polyatomic Cations Ammonium NH4+ Hydronium H3O+ Nitronium NO2+ Uranyl UO22+ Vanadyl VO2+ Mercury(I) Hg22+ Mercurous

Common Anions Formal Name Formula Alt. Name Simple Anions Arsenide As3− Azide N3− Bromide Br− Chloride Cl− Fluoride F− Hydride H− Iodide I− Nitride N3− Oxide O2− Phosphide P3− Sulfide S2− Peroxide O22− Oxoanions Arsenate AsO43− Arsenite AsO33− Borate BO33− Bromate BrO3− Hypobromite BrO− Carbonate CO32− Hydrogen carbonate HCO3− Bicarbonate Hydroxide OH− Chlorate ClO3− Perchlorate ClO4− Chlorite ClO2− Hypochlorite ClO− Chromate CrO42− Dichromate Cr2O72− Iodate IO3− Nitrate NO3− Nitrite NO2− Phosphate PO43− Hydrogen phosphate HPO42− Dihydrogen phosphate H2PO4− Permanganate MnO4− Phosphite PO33− Sulfate SO42− Thiosulfate S2O32− Hydrogen sulfate HSO4− Bisulfate Sulfite SO32− Hydrogen sulfite HSO3− Bisulfite Anions from Organic Acids Acetate C2H3O2− Formate HCO2− Oxalate C2O42− Hydrogen oxalate HC2O4− Binoxalate Other Anions hydrosulfide HS− Bisulfide Telluride Te2− Amide NH2− Cyanate OCN− Thiocyanate SCN− Cyanide CN−

See also

• Air ionizer
• Cathode
• Anode

External links

• Department of Education, Newfoundland and Labrador-Canada "Template:PDFlink". A Periodic table reporting ionic charges for every chemical element.