Trigonal pyramidal molecular geometry

Trigonal pyramidal molecular geometry

Infobox molecular geometry

Symmetry_group= C3v
Bond_angle=<109.5º, ≈107º
Examples= NH3, PCl3

In chemistry, a trigonal pyramid is a molecular geometry with one atom at the apex and three atoms at the corners of a trigonal base. When all three atoms at the corners are identical, the molecule belongs to point group "C3v"Fact|date=January 2008. One example of a molecule with a trigonal pyramidal geometry is ammonia (NH3). Some molecules and ions with trigonal pyramidal geometry include the xenon trioxide molecule, XeO3, the chlorate ion, ClO3, the sulfite ion, SO32−, and the phosphite ion, PO33−. In organic chemistry, molecules which have a trigonal pyramidal geometry are sometimes described as sp3 hybridized. The AXE method for VSEPR theory states that the classification is AX3EFact|date=January 2008.

Trigonal pyramidal geometry in ammonia

The nitrogen atom in ammonia has 5 valence electrons and bonds with three hydrogen atoms to complete the octet. This would result in the geometry of a regular tetrahedron with each bond angle cos−1(−⅓) ≈ 109.5°. However, the three hydrogen atoms are repelled by the electron lone pair in a way that the geometry is distorted to a trigonal pyramid (regular 3-sided pyramid) with bond angles of 107°. In contrast, boron trifluoride is flat, adopting a trigonal planar geometry because the boron does not have a lone pair of electrons.

In ammonia the trigonal pyramid undergoes rapid nitrogen inversionC. E. Cleeton & N. H. Williams, 1934 - [ Online version; archive] . URL last accessed 8 May 2006] .


ee also

*AXE method
*Molecular geometry

External links

* [ Chem| Chemistry, Structures, and 3D Molecules]
* [| Indiana University Molecular Structure Center]
* [ Point Group Symmetry| Point Group Symmetry Interactive Examples]
* [| Molecular Modeling]
* [| Animated Trigonal Planar Visual]

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