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CHEM 121 Studioby Learn4Less · UBC CHEM 121

CHEM 121 glossary

Electron affinity

The energy change when a gaseous atom gains an electron, X(g)+eX−→XX−(g)\ce{X(g) + e- -> X-(g)}. Many tables list the energy released as a positive number; the most is released toward the upper right of the table, peaking at chlorine rather than fluorine.

Bar chart of values in kJ/mol releasedF: 328 kJ/mol released; Cl: 349 kJ/mol released; Br: 325 kJ/mol released; I: 295 kJ/mol released0100200300400kJ/mol released328F349Cl325Br295I

The halogens: Cl releases the most; fluorine's small 2p2p shell repels the added electron.

Example

Down group 17 the energy released falls from Cl (349) to Br (325) to I (295 kJ/mol), because the added electron sits farther from the nucleus.

See alsoIonization energyAnionEffective nuclear chargeElectronegativity