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