Question

Why do nitrogen and phosphorus have high ionisation energies?

Answer 1

Well, because they are non-metal atoms, oxidizing agents, with relatively high, unshielded nuclear charge.....

Explanation:

So let us find some data....

AS nuclear charge increases, the ionization energy should also increase across the Period. However, there is a DECREASE in ionization energy observed for nitrogen, and oxygen, and for phosphorus and sulfur.

And note that we interrogate the ionization reactions....

`N(g)+DeltararrN^(+)(g) + e^(-)`

`P(g)+DeltararrP^(+)(g) + e^(-)`

The apparent anomalous ionization energy of nitrogen versus oxygen, is probably a consequence of Hund's rule of maximum multiplicity....the spin quantum number of the nitrogen atom is maximized here, with three unpaired electrons...and the `3p^3` electrons have a energetically stable configuration.....