Ionisation Energy

Ionisation energy may be defined as, “the amount of energy required to remove the most loosely bound electron from an isolated gaseous atom.”

M (g)   +   Energy (I.E)   ----->    M⁺ (g)    +    e ^–

Ionisation energy is also called Ionisation Potential. It is most expressed in terms of electron volts (e.v) (1 e.v = 1.603 ´ 10 ^{– 19} J).