Trigonal pyramidal molecular geometry
- Trigonal pyramidal molecular geometry
Infobox molecular geometry
Symmetry_group= C3v
Electron_direction=4
Atom_direction=3
Bond_angle=<109.5º, ≈107º
mu=
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 inversion[C. E. Cleeton & N. H. Williams, 1934 - [http://prola.aps.org/abstract/PR/v45/i4/p234_1 Online version; archive] . URL last accessed 8 May 2006] .]
References
ee also
*AXE method
*Molecular geometry
External links
* [http://www.3dchem.com/3D Chem| Chemistry, Structures, and 3D Molecules]
* [http://www.iumsc.indiana.edu/IUMSC| Indiana University Molecular Structure Center]
* [http://www.phys.ncl.ac.uk/staff/njpg/symmetry/Molecules_l3d.html Point Group Symmetry| Point Group Symmetry Interactive Examples]
* [http://chemlab.truman.edu/CHEM121Labs/MolecularModeling1.htm| Molecular Modeling]
* [http://intro.chem.okstate.edu/1314F97/Chapter9/3BP.html| Animated Trigonal Planar Visual]
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