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Polyatomic ion

A polyatomic ion or molecule ion is an ion consisting of covalently bonded atoms that can be considered as acting as a single unit in the context of acid/base chemistry or in the formation of salts. For more information on polyatomic ions containing metals, and how to name these, see metal complex. Note, a polyatomic ion is also referred to in older works as a radical. In current usage the term radical refers to free radicals which are uncharged species with an unpaired electron.

Some commonly-occurring polyatomic ions and their charges are indicated below:

The atoms of a polyatomic ion are always associated with each other via covalent or coordinate-covalent bonds.

A large polyatomic ion will often be considered as the conjugate acid or conjugate base of a neutral molecule, for example the conjugate acid of adrenaline at the amine group.

Note that many of the common negatively-charged (anionic) polyatomic ions are conjugate bases of acids derived from the oxides of non-metallic elements. For example sulfate or SO42- ion is derived from H2SO4 which can be regarded as SO3 + H2O.

Bicarbonate is also called hydrogen carbonate in modern chemical nomenclature.

Last updated: 02-10-2005 17:06:00
Last updated: 02-26-2005 20:52:47