Second ionisation enthalpies of alkali metals are much higher than those of the alkaline earth metals. Explain.
Alkali metals have only one valence electron, while alkaline earth metals have two valence electrons. After the removal of one electron from alkali metals, they form M+which is a stable noble gas configuration. Removal of another electron from the unipositive ion of alkali metal, therefore, would require a very large amount of enthalpy.
On the other hand, after the removal of one electron from alkaline earth metals, they do not acquire stable noble gas configuration and still have a tendency to lose another electron. As a result, the second ionisation enthalpies of alkali metals are much higher than those of the alkaline earth metal.