Question

How would you explain the fact that the first ionization enthalpy of sodium is lower

than that of magnesium but its second ionization enthalpy is higher than that of

magnesium.

Answer 1

Electronic configuration:

Na: [Ne] 3s¹

Mg:[Ne] 3s²

Sodium(Na) has only one valence electron.By loosing this electron, it attains stable configuration.Therefore, its first ionization energy is less than magnesium(Mg).

After removal of an electron, sodium attains configuration of noble gas Neon whereas magnesium has one valence electron.To remove an electron from, this configuration requires lot of energy.Therefore, its second ionization energy is more than magnesium.