Polyatomic ion
A polyatomic ion is an ion consisting of multiple atoms associated together by covalent bonds which can be considered as acting as a single unit in the context of acid/base chemistry or in the formation of salts. Note that in this context, a polyatomic ion is also referred to as a radical.
Some commonly-occurring polyatomic ions and their charges are
indicated below
carbonate CO32-
bicarbonate HCO3-
nitrate NO3-
phosphate PO43-
sulfate SO42-
acetate CH3C(=O)O-
ammonium NH4+
hydroxide OH-
pyridinium C5H5NH+
The atoms of a polyatomic ion are always associated with
each other via covalent or coordinate-covalent bonds.
A polyatomic ion that is primarily associated with other atoms by
covalent, rather than ionic, forces might more properly be referred to as a
functional group.
Note that many of the common negatively-charged (anionic) polyatomic ions are oxides of non-metallic elements, and can be considered the conjugate bases of the corresponding acids.
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