Why chlorine has more electron affinity than fluorine?

From a quantum chemistry perspective, it's all about orbital compactness and interelectronic repulsion:Fluorine (F): Small 2p orbitals High electron density in small space Strong repulsion for additional electron Electron affinity: ~328 kJ/molChlorine (Cl): Larger 3p orbitals * Electron cloud more spread out Less repulsion for additional electron Electron affinity: ~349 kJ/molThe size factor* dominates here - despite fluorine's stronger nuclear charge, the repulsion in its compact orbitals reduces the stability gained from adding an electron. This is a great example of how multiple factors (nuclear charge, atomic size, electron repulsion) compete in determining periodic trends. The trend continues downward - bromine has slightly lower EA than chlorine due to increased distance from nucleus.

This is a classic chemistry question! Chlorine has higher electron affinity than fluorine due to atomic size and electron repulsion: Fluorine atom is very small (atomic radius ~50 pm) Chlorine atom is larger (atomic radius ~100 pm)In fluorine's small atomic structure, the incoming electron experiences significant electron-electron repulsion from the existing electrons in the compact 2p orbital. This repulsion reduces the energy released when fluorine gains an electron.Chlorine's larger size means the incoming electron is further from the nucleus but experiences less repulsion from other electrons in the more spread-out 3p orbital. The balance favors chlorine - the reduced repulsion outweighs the smaller nuclear attraction at the larger distance.So while fluorine is more electronegative (stronger pull on bonded electrons), chlorine actually releases more energy when gaining an extra electron!