Electron Afinity: Definition, example, trend in periodic table

Electron Affinity

Electron affinity may be defined as the amount of energy released when an electrons add up in the valence shell of an isolated gaseous atom.

X + e ⎯⎯→ X- + electron affinity

Units

Units of electron affinity are kJ/mole-1 or kJ/mole.

Trend in Periodic Table

In period: Generally, electron affinity values of elements increase from left to right within the period. In fact, that atomic size decreases and nuclear charge (atomic number) gradually increases on moving left to right within the period. As a result, nucleus bind with incoming extra electron more tightly and hence has more electron affinity.

For example, halogens have higher electron affinity than alkali metals in each period because of smaller atomic size and greater nuclear charge than alkali metals.

In group: Electron affinity decreases from top to bottom within the group because size of atom and shielding effect increase which results in decrease in attractive forces between nucleus and incoming extra electron. As a result, electron affinity decreases down the group.

For example, F has higher electron affinity than other halogens due to smaller size and lesser shielding effect than other halogens.

Electronegativity: Electronegativity may be define as the ability of an atom to attract the electrons towards itself in covalent bond.

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