A positively charged ion is known as cation. For example : Sodium ion:Na , Magnesium ion: Mg2 A cation is formed by the loss of one or more electrons by an atom For example : sodium atom, loses one electron to form a sodium ion Na Sodium atom (A cation)

A negatively charged ion is known as anion. Cl- (chloride ion), O-2 (oxide ion) etc. An anions is formed by the gain of one or more electrons by an atom. For example a chlorine atom gains one electron to form a chloride ion Cl-. Chlorine atom Chloride ion (An anion).