Question

Electron gain enthalpy of chlorine is more negative value as compared to that of flourine (F). Why?

Answer 1

The size of fluorine atom is small. As a result there are strong electron -electron repulsions in the 2p orbital.
Any upcoming electron into the atom feels a large amount of repulsion by the electron cloud of F and thus its not easy for the electron to enter into the atom.

Thus electron gain enthalpy of fluorine is less negative than that of chlorine.

Answer 2

Explanation:

Electron gain enthalpy of F is less negative than that of Cl because when an electron is added to F,the added electron goes to the smaller n=2 quantam level and suffers repulsion from other electons present in this level. In case of Cl,the added electron goes to the larger n=3 quantam level and suffers much less repulsion from other electron.

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