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| Trigonal pyramidal molecular geometry | |
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| Examples | NH3, PCl3 |
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| Point group | C3v |
| Steric number | 4 |
| Coordination number | 3 |
| Bond angle(s) | <109.5º, ≈107º |
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 C3vcitation needed. 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 AX3Ecitation needed.
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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 inversion1.
References
- ^ C. E. Cleeton & N. H. Williams, 1934 - Online version; archive. URL last accessed 8 May 2006
See also
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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Wikipedia content modification information:
- This page was last modified on 2 September 2008, at 01:17.
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