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CHEM 121 Studioby Learn4Less · UBC CHEM 121

CHEM 121 glossary

Incomplete octet

A central atom with fewer than 8 valence electrons in its best Lewis structure. It is typical of B and Be (and gas-phase Al halides), which form only single bonds to halogens and keep formal charges at zero.

ClBeCl
BeClX2\ce{BeCl2}: Be has only 4 electrons.

Example

BClX3\ce{BCl3} has 3+3(7)=243 + 3(7) = 24 valence electrons: three B–Cl bonds plus three lone pairs on each Cl use all 24, leaving B with 6. Such electron-deficient atoms accept a lone pair, acting as Lewis acids.

See alsoOctet ruleLewis acidExpanded octetRadical