What is ionisation energy?

The easiest way to understand ionisation energy is to look at the equation for ionisation.For example, the ionisation of magnesium is shown by the following:Mg---> Mg⁺ + e^- The ionisation energy is then the energy required for this process to take place. Technically, the definition of ionisation energy is the energy required to remove one electron from every atom in a mole of atoms.