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CHEM 121 Studioby Learn4Less · UBC CHEM 121

CHEM 121 glossary

Expanded octet

A central atom holding more than 8 valence electrons. It is possible only for atoms in period 3 or below (P, S, Cl, Br, I, Xe, …); period-2 atoms never expand.

SFFFF
SFX4\ce{SF4}: S has 4 bonds and 1 lone pair, 10 electrons in all.

Example

IClX4X−\ce{ICl4-}: 7+4(7)+1=367 + 4(7) + 1 = 36 e⁻. After four I–Cl bonds and the Cl octets, 4 electrons remain as 2 lone pairs on I, which then holds 12 electrons.

See alsoOctet ruleIncomplete octetCentral atom