Why is electron gain enthalpy of fluorine is less negative than that of chlorine

Generally as we go down a group electron gain enthalphy decreases. Accordingly Fluorine should have higher negative electron gain enthalphy. But this is not so. Chlorine has higher negative electron gain enthalphy. The reason is when an electron is added to fluorine,it goes to a compact second level energy cell where electro-electrn repulsion is more and hence negative electron gain enthalphy is less. But in Chlorine additional electron goes to larger third level energy cell where electron-electron repulsion is less due to large size and thus has higher negative electron gain enthalphy

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