Chemical Species

Ion - Any specie that contains charge knowns as Ion that charge can be negative (Anion) or it be positive (Cation) e.g. $Na^{+}{1},O^{-2}$.

Anion - An atom or group of atom that has a negative charge on it e.g. - Cl - (negative )

Cation - An atom or group of atom that has a positive charge on it e.g. Na+.

Molecular ions - when a molecule loses or gains electrons called molecular ions. it can be positive or negative for example $CH_4^+$.

Free Radical - Free radicals are atoms and group of atoms having number of unpaired electrons - . It is represented by putting a dot over the symbol of an element.