Nitrogen has positive electron gain enthalpy whereas oxygen has negative. However, oxygen has lower ionisation enthalpy than nitrogen. Explain.

Explanation

The outermost electronic configuration of nitrogen `(2s^(1) 2p_(x)^(1) 2p_(y)^(1) 2p_(z)^(1))` is quite since it has exactly half- filled 2p - orbitals . Therefore it has no tendency to accept an extra electron. In other words energy has to be supplied to add an extra electron. thus electron gain enthalpy of N is slightly positive . In contrast, outermost elecronic configuration of O is `2s^(2) 2p_(x)^(2) 2p_(y)^(1) 2p_(z)^(1)` . It has highest nuclear charge ( + 8) than N (+7) and hence it has a high tendency to accept an extra electron . In other words energy in released when an electron is added to O and Hence electron gain enthalpy of O is highly negative .Further since O has four after losing one electron therefore ionization enthalpy of O is lower than that of N.