Monatomic ion

A monatomic ion is an ion consisting of one or more atoms of a single element (unlike a polyatomic ion, which consists of more than one element in one ion). For example calcium carbonate consists of the monatomic ion Ca2+ and the polyatomic ion CO32-.

A type I binary ionic compound contains a metal (cation) that forms only one type of ion. A type II ionic compound contains a metal that forms more than one type of ion, i.e., ions with different charges.