The second ionisation enthalpy of the elements of group `1` are higher than those of elements of group `2`. Explain.

Explanation

The second electron in case of alkali metals is to be removed from unipositive cation which has acquired highly stable noble gas configuration, e.g.
`underset([Ne]3s^(1))(Na)overset(IE_(1))underset(-e^(-))rarr underset(underset(underset("gas configuration")("Stable noble"))([Ne]3s^(0)))(Na^(+)) overset(IE_(2))underset(-e^(-))rarrNa^(2+)`
Whereas in case of alkaline earth metals, the seconds electron is to be removed from a cation which will acquire the stable noble gas configuration after the removal of second electron, e.g.
`underset([Ne]3s^(1))(Na) overset(IE_(1))underset(-e^(-))rarr underset([Ne]3s^(1))(Mg^(o+))overset(+IE_(2))underset(-e^(-))rarr underset([Ne]3s^(0))(Mg^(2+))`
That is whyc the second ionisation enthalpy of ground 1 elements is much higher than those of group 2 elements.