Which halogen has the highest electron affinity?

Electron affinity is the energy change when an atom gains an electron. Among halogens, electron affinity generally decreases down the group: fluorine < chlorine > bromine > iodine.

Chlorine has the highest electron affinity. Although fluorine is more electronegative, its small atomic size causes strong electron-electron repulsion in the small 2p orbital. This reduces its ability to accept an extra electron compared to chlorine. Chlorine, with a larger 3p orbital, can accommodate an additional electron more comfortably, releasing more energy.

Bromine and iodine have lower electron affinities because as we go down the group, atomic size increases and the added electron is farther from the nucleus, making the energy released smaller. Electron affinity reflects how strongly an atom attracts electrons, which influences chemical reactivity, especially for halogens.

Halogens like chlorine are strong oxidizing agents due to their high electron affinity, making them useful in chemical synthesis, water purification, and disinfection. Understanding these properties helps students predict reaction behavior, such as displacement reactions and halogen reactivity trends.

This question highlights periodic trends in electron affinity and shows why chlorine is highly reactive among halogens. Knowing which halogen has the highest electron affinity is key to understanding halogen chemistry and redox behavior in inorganic chemistry.