Discuss the general trends in ionisation enthalpy of the alkaline earth metals.

i) The alkaline earth metals owing to their large size of atoms have fairly low values of ionisation enthalpies. Within the group, the ionisation enthalpy decreases as the atomic number increases. It is because of increase in atomic size due to the addition of new shells and increase in the magnitude of screening effect of the electrons in inner shells.

ii) The first ionisation enthalpies of alkaline earth metals are higher than alkali metals because of smaller atomic size and higher than alkali metals because of smaller atomic size and higher effective nuclear charge. Second ionisation enthalpy  is smaller than that of alkali metals because alkali metals acquire noble gas configuration after losing one electron.