An ion is a material, atom, or molecular structure where the numbers of electrons and protons are not equal. An ion with more electrons is called an anion, and an ion with more protons a cation. Ionized materials are further categorized by their composition. An ionic material consisting of one element is a monatomic ion, An ionic material with more than one element is a polyatomic ion.
Ions are created by the addition or removal of electrons by stripping by radiation, or by acquiring electrons through chemical action. Ionic electrons are outer shell electrons, which are easier to separate from the atomic structure than the more tightly held electrons in the inner shells.