Polyatomic ion

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

A polyatomic ion is a molecule that bears ionic groups, that is, a molecule with a charge. The majority of biological compounds and inorganic species conform to this strict definition. Ordinarily however, the term refers to small collections of atoms, 3 to perhaps 50 atoms, such as many metal complexes and oxyanions such as sulfate. in Greek, the prefix poly- means "many," which to a chemist means three or more atoms.

Hydroxide ions and ammonium ions

* A hydroxide ion is made of one oxygen atom and one hydrogen atom: its chemical formula is (OH)−. It has a charge of −1.
* An ammonium ion is made up of one nitrogen atom and four hydrogen atoms: its chemical formula is (NH4)+. It has charge of +1.

A polyatomic ion can often be considered as the conjugate acid or conjugate base of a neutral molecule. For example the sulfate anion, SO42−, is derived from H2SO4 which can be regarded as SO3 + H2O.

There are two "rules" that can be used for the learning the nomenclature of polyatomic ions. First, when the prefix bi- is added to a name, a hydrogen is added to the ion's formula and its charge is increased by 1. It is a consequence of the hydrogen ion carrying a +1 charge. An alternate to the bi- prefix is to use the word hydrogen in its place: the anion derived from H+ + CO32−, HCO3− can be called either bicarbonate or hydrogencarbonate.

The second rule looks at the number of oxygens in an ion. Consider the chlorine oxoanion family:
oxidation state −1 +1 +3 +5 +7
anion name chloride hypochlorite chlorite chlorate perchlorate
formula Cl− ClO− ClO2− ClO3− ClO4−
structure The chloride ion The hypochlorite ion The chlorite ion The chlorate ion The perchlorate ion

First, think of the -ate ion as being the "base" name, in which case the addition of a per- prefix adds an oxygen. Changing the -ate suffix to -ite will reduce the oxygens by one, and keeping the suffix -ite and adding the prefix hypo- reduces the number of oxygens by two. In all situations, the charge is not affected.

It is important to note that these rules will not work with all polyatomic ions, but they do work with the most common ones (sulfate, phosphate, nitrate, chlorate).
Contents
[hide]

* 1 Polyatomic ions vs. radicals
* 2 List of polyatomic ions
* 3 See also
* 4 External links

[edit] Polyatomic ions vs. radicals

Although most polyatomic ions are diamagnetic (all electrons are paired), some are radicals. Some radicals are charged and as such are polyatomic ions, such as the radical anion of naphthalene, C10H8-. Some can be used in decomposition reactions, providing spectacular results, such as H2, O2 and iodine.

[edit] List of polyatomic ions

Caution: chemists classify ions and molecules even when such species do not exist to any appreciable extent. For example, small ions with high charges are very rare, as illustrated by the fact that oxide, O2-, has not been observed in solution and is not considered as a component in reaction mechanisms. Similarly, orthosilicate, SiO44- enjoys no status as an ion in aqueous solution, except perhaps under extreme temperatures. In general, ions that have charges greater than 2- do not exist in solution unless they are protonated.
Polyatomic ions
Acetate CH3COO− or C2H3O2−
Aluminate AlO2−, Al2O42−
Amide NH2−
Ammonium NH4+
Antimonate SbO43−
Antimonite SbO33−
Arsenate AsO43−
Arsenite AsO33−
Azide N3−
Benzoate C6H5COO−
Bicarbonate (hydrogen carbonate) HCO3−
Borate BO33−
Metaborate BO2−
Tetraborate B4O72−
Bromate BrO3−
Bromite BrO2−
Carbide C22−
Carbonate CO32−
Chlorate ClO3−
Chlorite ClO2−
Chromate CrO42−
Chromite CrO2−
Chromyl CrO22+
Citrate C6H5O73−
Cyanate OCN−
Cyanide CN−
Dichromate Cr2O72−
Dihydrogen arsenate H2AsO4−
Dihydrogen phosphate H2PO4−
Dihydrogen phosphite H2PO3−
Dioxygenyl O2+
Disulfide S22−
Ferrate FeO42−
Ferricyanide Fe(CN)63−
Ferrocyanide Fe(CN)64−
Formate (formiate) HCO2−
Fulminate CNO−
Hydrazide N2H3−
Hydrogen carbonate (bicarbonate) HCO3−
Hydrogen arsenate HAsO42−
Hydrogen phosphate HPO42−
Hydrogen phosphite HPO32−
Hydrogen sulfate HSO4−
Hydrogen sulfite HSO3−
Hydrogen telluride HTe−
Hydronium H3O+
Hydroxide OH−
Hypobromite BrO−
Hypochlorite ClO−
Hypoiodite IO−
Hypophosphite PO23−
Hyposulfite SO22−
Periodate IO4−
Iodate IO3−
Iodite IO2−
Isocyanate NCO−
Mercury(I) Hg22+
Manganate MnO42−
Molybdate MoO42−
Nitrate NO3−
Nitrite NO2−
Oxalate C2O42−
Ozonide O3−
Perbromate BrO4−
Perchlorate ClO4−
Permanganate MnO4−
Peroxide O22−
Perrhenate ReO4−
Peroxymonosulfate SO52−
Peroxydisulfate S2O82−
Pertechnetate TcO4−
Phosphate PO43−
Phosphite PO33−
Plumbate PbO32−
Plumbite PbO22−
Pyridinium C5H6N+
Pyrophosphate P2O74−
Pyrylium C5H5O+
Quaternary ammonium NR4+
Selenate SeO42−
Selenite (ion) SeO32−
Silicate SiO32−
Disilicate Si2O52−
Metasilicate SiO32−
Orthosilicate SiO44−
Pyrosilicate Si2O76−
Stannate SnO32−
Stannite SnO22−
Sulfate SO42−
Sulfite SO32−
Sulfonium R3S+
Superoxide O2−
Tartrate (CH(OH)COO)22−
Metatellurate TeO42−
Orthotellurate TeO66−
Tellurite TeO32−
Thiocyanate SCN−
Thiosulfate S2O32−
Tosylate (toluenesulfonate) CH3C6H4SO3−
Triflate (trifluoromethanesulfonate) CF3SO3−
Tungstate WO42−
Uranyl UO2+
Vanadate VO3−
Vanadyl VO2+
Pervanadyl VO2+

[edit] See also

* Monatomic ion
* Salt
* Mass spectrometry
* Hydrogen peroxide
* Molecule
* Organic elements

[edit] External links

* List of polyatomic ions
* A Beginner's Guide To Polyatomic Ions.
* Tables of Common Polyatomic Ions. Also a source for PDB files (PDB information)

Retrieved from "http://en.wikipedia.org/wiki/Polyatomic_ion"

Category: Ions
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