The energy change when a gaseous atom gains an electron; halogens have the most negative values.
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Electron affinity is the energy change when a gaseous atom gains an electron to form a negative ion. A negative value means energy is released, as is typical for the halogens, which have the most negative values in the periodic table. Noble gases have values near zero or positive, because the added electron must enter a new shell or be strongly repelled. The second electron affinity of an atom is always positive, because adding an electron to a negative ion requires energy to overcome repulsion. Electron affinity helps explain why halide ions form readily.
Key ideas: The energy change when a gaseous atom gains an electron: X(g) + e- gives X-(g). Cl = -349 kJ per mol (most negative), F = -328, O = -141, N is about +7 (not favorable). A negative sign means energy release. Second electron affinity is positive since adding to an anion is repulsive (O- to O2- is +744).
Common mistakes and connections: Students confuse the sign convention (some books use positive for release) and think fluorine has the highest EA, but Cl is higher because F's small 2p orbital increases electron repulsion. Noble gases and group 2 have near zero or positive values. It leads to electronegativity and the Born-Haber cycle.
Halogens release a lot of energy on gaining an electron; chlorine is highest, since the small fluorine atom has extra electron repulsion. The interactive lesson shows this as a live animation or chart.
Chlorine releases about 349 kJ/mol when it gains an electron, the largest energy release of any element.
The energy change when a gaseous atom gains an electron; halogens have the most negative values.
Electron Affinity is a intermediate topic in Atomic Structure & Periodicity. It builds on the vocabulary of beginner topics in this area.
Study these earlier topics in Atomic Structure & Periodicity first: Ionization Energy, Successive Ionization Energies, Anomalies in Ionization Energy.
The next topics in Atomic Structure & Periodicity are Electronegativity and Pauling Scale.
Yes. The interactive lesson includes a self-check question on Electron Affinity, and the Atomic Structure & Periodicity quiz draws on every topic in this area.
Electron Affinity is topic 89 of 115 in Atomic Structure & Periodicity.