Polyatomic ion

The prefix poly- carries the meaning "many" in Greek, but even ions of two atoms are commonly described as polyatomic.

Often, a polyatomic ion can be considered as the conjugate acid or base of a neutral molecule.

For example, the conjugate base of sulfuric acid (H2SO4) is the polyatomic hydrogen sulfate anion (HSO−4).

An alternative to the bi- prefix is to use the word hydrogen in its place: the anion derived from H+.

Most of the common polyatomic anions are oxyanions, conjugate bases of oxyacids (acids derived from the oxides of non-metallic elements).

The following tables give additional examples of commonly encountered polyatomic ions.

An electrostatic potential map of the nitrate ion ( N O − 3 ). Areas coloured translucent red, around the outside of the red oxygen atoms themselves, signify the regions of most negative electrostatic potential.