Question

The first ionization energy of nitrogen is higher than that of oxygen or carbon. Explain.

Answer 1

It is natural to expect that oxygen has a higher ionisation energy than nitrogen due to the fact that the first ionisation energy increases across a period. This is because when moving from left to right, the atomic number increases which means that the nuclear charge increases. As a result, the valence electrons are held more tightly to the nucleus and hence we expect the first ionisation energy to increase across the group.