trigonal pyramidal arrangement
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A trigonal pyramidal arrangement describes a three-dimensional molecular shape where one atom is at the apex of a pyramid, and three other atoms form the triangular base. This geometry arises from the repulsion of electron pairs around a central atom, as explained by the Valence-Shell Electron-Pair Repulsion (VSEPR) theory.12
For example, ammonia (NH₃) exhibits a trigonal pyramidal shape. The nitrogen atom is at the center, bonded to three hydrogen atoms. While the electron pairs around the nitrogen atom would ideally arrange tetrahedrally, the presence of a lone pair of electrons pushes the bonding pairs closer together, resulting in the pyramidal structure. This shape is distinct from a trigonal planar arrangement, where all atoms lie in a single plane.12
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