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CHEM 121 Studioby Learn4Less · UBC CHEM 121

CHEM 121 glossary

Seesaw

The AX4E\mathrm{AX_4E} shape: a trigonal bipyramid with one equatorial lone pair, leaving two axial and two equatorial atoms. Its angles are a little below the ideal 90° and 120°.

Central S atom bonded to 4 F atoms, with 1 lone pair.FFSFF90°120°180°Ideal bond angles: 90°, 120°, 180°
SFX4\ce{SF4}: the equatorial lone pair pushes the four F atoms into a seesaw.

Example

SeFX4\ce{SeF4}, TeClX4\ce{TeCl4} and IFX4X+\ce{IF4+} are seesaw-shaped too. The shape cannot cancel its bond dipoles, so SFX4\ce{SF4} is polar.

See alsoTrigonal bipyramidalAxial and equatorial positionsT-shaped