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CHEM 121 Studioby Learn4Less · UBC CHEM 121

CHEM 121 glossary

Trigonal pyramidal

The AX3E\mathrm{AX_3E} shape: three atoms and one lone pair in a tetrahedral arrangement, so the central atom sits at the top of a low pyramid over a triangle of atoms. Bond angles are a little under 109.5°.

Central N atom bonded to 3 H atoms, with 1 lone pair.HHNH109.5°Ideal bond angle: 109.5°
NHX3\ce{NH3}: H–N–H ≈ 107°.

Example

HX3OX+\ce{H3O+}, PClX3\ce{PCl3} and ClOX3X−\ce{ClO3-} are all trigonal pyramidal. With polar bonds this shape is always polar.

See alsoTetrahedralLone pairPolar molecule