Question

Electron gain enthalpy of Cl is higher than F. Why?

Answer 1

Because due to small size of fluorine some energy is utilized in overcoming the force of repulsion between electrons, hence it has lesser value of electron affinity.

Answer 2

Answer:

Due to its small size, the electron–electron repulsions in the relatively compact 2p-sub-shell are comparatively large, and hence, the incoming electron is not accepted with the same ease as is the case with larger Cl atom. Consequently, electron gain enthalpy of Cl is more negative than that of F.