Question

Q.17. 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

The electronic configurations are as follows:

Na - [Ne] 3s

1

Mg - [Ne] 3s

2

Sodium has one valence electron in 3s

1

and by losing this electron it attains stable configuration. Therefore the 1st ionization energy of Na is less than Mg. After removing an electron the Na attains noble gas configuration whereas Mg has one electron left. To remove an electron from a noble gas configuration high energy is required.

Therefore the second ionization enthalpy is higher than that of magnesium.