E

Electron Affinity

EA = E(X) − E(X⁻); usually negative (exothermic for most nonmetals)
Quick Reference
Formula / NotationEA = E(X) − E(X⁻); usually negative (exothermic for most nonmetals)
Also Known AsElectron attachment energy, EA, electron gain enthalpy

What is Electron Affinity?

The energy change when a neutral gaseous atom gains an electron to form a negative ion. Elements with high electron affinity (like halogens) readily accept electrons. Generally increases across a period and decreases down a group in the periodic table.

Formula & Notation

EA = E(X) − E(X⁻); usually negative (exothermic for most nonmetals)

Other Names / Synonyms: Electron attachment energy, EA, electron gain enthalpy

Properties & Characteristics

Electron affinity (EA) is the energy change when a neutral gaseous atom gains one electron to form a gaseous anion: X(g) + e⁻ → X⁻(g). By convention, a negative EA indicates energy is released (exothermic, favourable). Most nonmetals have negative EA (Cl: −349 kJ/mol); noble gases and alkaline earth metals have positive EA (endothermic, unfavourable). EA increases across a period and generally decreases down a group. Second electron affinity is always endothermic.

Uses & Applications

Electron affinity values are used in Born-Haber cycle calculations to determine lattice energies, in assessing the oxidising power of elements, in explaining the stability of anions, and in predicting the reactivity of nonmetals toward electron-rich reagents.

Safety Information

No direct safety concern for the concept. Elements with strongly negative EA (F₂, Cl₂) are powerful oxidisers and require appropriate containment and PPE. The high EA of halogens explains their extreme reactivity.

Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.

Key Facts

Term Electron Affinity
Formula EA = E(X) − E(X⁻); usually negative (exothermic for most nonmetals)
Synonyms Electron attachment energy, EA, electron gain enthalpy

Frequently Asked Questions

The energy change when a neutral gaseous atom gains an electron to form a negative ion. Elements with high electron affinity (like halogens) readily accept electrons. Generally increases across a period and decreases down a group in the periodic table.

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