The ability of an element to give away its outermost electrons to form positive ions is manifested in the amount of energy supplied to its atoms sufficiently enough to take away the electrons out of them. This energy is known as Ionisation Energy. Simply speaking, the Ionisation Energy is the energy supplied to an isolated atom or molecule to knockout its most loosely bound valence shell electron to form a positive ion. Its unit is electron-volt eV or kJ/mol and is measured in an electric discha