Monatomic ion

A monatomic ion (also called simple ion^[1][2]) is an ion consisting of exactly one atom. If, instead of being monatomic, an ion contains more than one atom, even if these are of the same element, it is called a polyatomic ion.^[3] For example, calcium carbonate consists of the monatomic cation Ca²⁺ and the polyatomic anion CO²⁻
₃; both pentazenium (N+5) and azide (N−3) are polyatomic as well.