Question

magnitude of electron gain enthalpy of f is less than of CL why?

Answer 1

Even though Fluorine has the highest electronegativity among all elements and it should have highest electron gain enthalpy among all Halogens

But

This is an exception and chlorine has higher electron gain enthalpy than Fluorine

The reason for this is that the size of Fluorine atom is very small and hence there is very high inter-electronic repulsion among the electrons of Fluorine

This makes incoming of another electron not favorable

Even though Fluorine has large negative electron gain enthalpy but for chlorine its even more negative

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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.