Question

Explain why electron gain enthalpy of flourine is lesser than that of Chlorine

Answer 1

The fluorine atom is smallerand has a higher effective nuclear charge than chlorine which result in very high inter-electronic repulsion among electrons of fluorine. ... Due to this electron gain enthalpy of fluorine is less negative than that of chlorine

Answer 2

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.