An atom or a group of atoms which carries positive or negative charge is called an ION
The ions containing positive charge is called cation and having negative charge is called anion
divalent cation - Mg^2+(magnesium)
divalent anionĀ - O^2-(oxide)
An ion is a chemical species with a net electrical charge formed when neutral atom or group of atoms accepts or denotes one more electrons.Ions are of 2 types-cations & anions.Cations are formed when neutral atom loses one or more electrons.It has less electrons than neutral atom & so is positively charged.Eg.Sodium atom(Na) on losing an electron forms sodium cation,denoted by Na+,calcium atom on losing 2 electrons forms calcium ion,denoted by Ca2+.Similarly,anions are formed when neutral atom gains one or more electrons.It has more electrons than the neutral atom & is so negatively charged.Chlorine forms a -ve ion,Cl-(anion) by accepting one electron.