Second ionization enthalpy (IE2) for alkali metals (Li, Na, K etc.) is very high as compared to their `IE_1` values. Explain why?

Explanation

This is due to following reasons:
(i) After the removal of first electron, the atom changes into a positive ion in which the electrons are held more tightly by the nucleus.
(ii) The second electron is to be removed from a lower shell and more energy is required for this purpose.
(iii) Positive ion formed by the removal of first electron in case of alkali metals has a stable noble gas configuration. Due to the similar reasons, the third I.E. values for Be and Mg are also very high.