Question

Question #14352

Answer 1

Oxygen has a complete pair of electrons in one of its 2p orbital and this causes more shielding (repulsion) which makes it easier to remove one of the electrons unlike nitrogen.

Explanation:

The electronic configurations of nitrogen and oxygen are:

Nitrogen: `1s^2 2s^2 2p^3`
Oxygen: `1s^2 2s^2 2p^4`

This means in their outermost p orbitals, Nitrogen has a pair of electron and one unpaired electron while Oxygen has 2 paired electrons.
Due to this difference, Oxygen experiences a greater shielding effect and requires less ionization energy.

N.B:
Mostly when explaining differences in ionization potentials, it is common to use differences in the electronegativities of the elements being compared. Nitrogen is higher up the electronegative series when compared with oxygen so this can't be the reason.