nitroge has positive electron gain enthalpy whereas oxygen has negative,however oxygen has lower ionization enthalpy than nitrogen.explain.

Electronic configuration:
N = 1s2 2s2 2p3 
O = 1s2 2s2 2p4

Nitrogen has a stable configuration with half filled 2p orbitals. Therefore, its ionisation enthalpy is more than oxygen.

Due to the presence of half filled 2p orbitals, nitrogen donot possess the tendency to gain electrons. Thus energy has to be supplied to nitrogen atom for gaining an electron. Thus, it has a positive electron gain enthalpy.

Oxygen on the other hand has a tendency to gain electrons. Thus energy would be released while gaining an electron. So, electron gain enthlapy of oxygen is negative. 

​So, it can be concluded that an atom having higher ionisation enthalpy doesnot necessarily have a negative electron gain enthalpy.


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