Flexi Says: Electron affinity is the energy released when an atom gains an electron. Electron affinity increases across the period and decreases down the group. Halogens have high electron affinity. However, chlorine has a higher electron affinity than fluorine. The fluorine has seven electrons in the second shell, and there will be considerable repulsion between the electrons in the tightly packed 2p subshell. Therefore, fluorine has a lesser tendency to accept electrons than chlorine.