Nitrogen has positive electron gain enthalpy whereas oxygen has negative. However, oxygen has lower ionisation enthalpy than nitrogen. Explain.
Electronic cofiguration of N = ${{1s}^{2}}$ ${{2s}^{2}}$ ${{2px}^{1}}$ ${{2py}^{1}}$ ${{2pz}^{1}}$
Nitrogen has stable configuration because /(-orbital is half-filled. Therefore, addition of extra electron to any of the /(-orbital requires energy.
Electronic configuration of O = ${{1s}^{2}}$ ${{2s}^{2}}$${{2px}^{2}}$${{2py}^{2}}$${{2pz}^{2}}$
Oxygen has ${{2p}^{4}}$ electrons,'so process of adding an electron to the /(-orbital is exothermic.
Oxygen has lower ionisation enthalpy than nitrogen because by removing one electron from 2/>-orbital, oxygen acquires stable configuration, i.e., ${{2p}^{3}}$. On the other hand,
in case of nitrogen it is not easy to remove one of the three 2p-electrons due to its stable configuration.