POLYATOMIC ION

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 ()⁻. It has a charge of −1.

★ An ammonium ion is made up of one nitrogen atom and four hydrogen atoms: its chemical formula is ()⁺. 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, ²⁻, 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	−	−	−	−	−
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

Polyatomic ions vs. radicals

List of polyatomic ions

See also

External links

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 , and iodine.

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, O^2-, has not been observed in solution and is not considered as a component in reaction mechanisms. Similarly, orthosilicate, SiO₄^4- 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+

See also

★ Monatomic ion

★ Salt

★ Mass spectrometry

★ Hydrogen peroxide

★ Molecule

★ Organic elements

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)