An electrically charged atom or group of atoms formed by the loss or gain of one or more electrons is called an Ion.
Cation:
An ion is a cation (positive ion) if it is created by electron loss and is attracted to the cathode in electrolysis.
Anion:
An ion is an anion (negative ion) if it is created by an electron gain and is attracted to the anode.
The valence of an ion is equal to the number of electrons lost or gained and is indicated by a plus sign for cations and a minus sign for anions.
Ex: Na +, Cl−, Ca ++,...
