Monatomic ion

A monatomic ion (also called simple ion ) 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. For example, calcium carbonate consists of the monatomic cation Ca2+ and the polyatomic anion ; both pentazenium (N5+) and azide (N3-) are polyatomic as well.