Define ionization energy. The first ionization energy of Nitrogen is greater than that of Oxygen - give appropriate reason.

Explanation

Ionisation energy is defined as ''The minimum amount of energy required to remove the most loosely bound electron from the valence shell of the isolated neutralgaseous atoms in its ground state''. Nitrogen `(1s^(2), 2s^(2),2p^(3)) (1402 "kJ mol"^(-1))` has higher ionisation energy that Oxygen `(1s^(2), 2s^(2), 2p^(3)) (1314 "kJ mol"^(-1))`.
Since the half - filled electronic configuration is more stable, it requires higher energy to remove an electron from 2p orbital of nitrogen. Whereaas the removal one 2p electron from oxygen atoms leads to a stable half - filled configuration. This makes comparatively easier to remove 2p electron from oxygen.