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.