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CHEM 121 Studioby Learn4Less · UBC CHEM 121

CHEM 121 glossary

Steric number

The number of electron domains on a central atom: SN = (atoms bonded to it) + (lone pairs on it). SN 2, 3, 4, 5, 6 give linear, trigonal planar, tetrahedral, trigonal bipyramidal and octahedral electron-domain geometries.

Central Xe atom bonded to 2 F atoms, with 3 lone pairs.FXeF180°Ideal bond angle: 180°
XeFX2\ce{XeF2}: 2 atoms + 3 lone pairs, SN = 5.

Example

SOX2\ce{SO2}: 2 bonded O + 1 lone pair, SN = 3. BrFX5\ce{BrF5}: 5 bonded F + 1 lone pair, SN = 6.

See alsoElectron domainElectron-domain geometryAXE notationCentral atom