Molecular geometry for nh3

Ammonia, NH₃, has trigonal pyramidal molecular geometry in the usual VSEPR model. Nitrogen has three bonding domains and one lone pair. The four electron domains have a tetrahedral arrangement, but the atom positions form a pyramid.

Meaning and context

Electron-domain geometry includes lone pairs as well as bonds. Molecular geometry describes the arrangement of atoms. That distinction explains why tetrahedral and trigonal pyramidal can both appear in an accurate discussion of the same molecule.

Examples and usage

A common approximate H–N–H bond angle is about 107°, slightly below the ideal tetrahedral angle. The lone pair and the bonding environment affect the actual geometry; a simple model should not imply that every four-domain species has exactly the same angle.

What to check

Start with the total valence-electron count and a valid Lewis structure before assigning a shape. The NH₄⁺ ion is a different species with different central-atom lone-pair bookkeeping. A formula’s charge matters.

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