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CHEM 121 Studioby Learn4Less · UBC CHEM 121

CHEM 121 glossary

VSEPR theory

Valence-shell electron-pair repulsion: the electron domains around a central atom repel one another and spread out to be as far apart as possible. The number of domains fixes the electron-domain geometry, and the lone pairs among them decide the molecular shape.

Central S atom bonded to 4 F atoms, with 1 lone pair.FFSFF90°120°180°Ideal bond angles: 90°, 120°, 180°
SFX4\ce{SF4}: five domains (four bonds, one lone pair) around S give a seesaw.

Example

PClX3\ce{PCl3}: 3 bonds + 1 lone pair on P = 4 domains, tetrahedral arrangement, so the molecule is trigonal pyramidal.

See alsoElectron domainSteric numberElectron-domain geometryMolecular geometry