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Introduction
Linear Combination of Atomic Orbitals
Larger Molecules
Reactions
Elementary Symmetry
Symmetry Elements
Point Groups
Irreducible Representations
Degenerate Orbitals
Glossary
Molecules in VRML
General Information - Installation - Use
| 5.2. Point Groups Point groups are mathematical entities defined by group theory that describe the complete symmetry of an object or moelcule (i.e. all its symmetry elements). It is necessary to determine the point group of a molecule in order to be able to use its symmetry to determine, for instance, the symmetries of the molecular vibrations or molecular orbitals. It is not, however, necessary to recognise all the symmetry elements of a molecule in order to be able to determine its point group. Figure 5.11 gives a simple scheme that allows the point group to be determined by recognising only key symmetry elements. Figure 5.11 A simple scheme for determining the point group of a molecule. The most common point groups are C1 (no symmetry at all) and Cs (just one mirror plane). The Cn, Cnv and Cnh point groups have just one proper rotation axis of order n and are distinguished from each other by their mirror planes. The Dn, Dnh and Dnd point groups are those with additional C2-axes perpendicaular to the principal axis. The point groups of the molecule shown in the molecular orbital plots are given in the long list of molecules in Sect. 6, so that you can try to use Figure 5.11 to reproduce these point group assignments in order to familiarise yourself with the concept. Symmetry Elements Point Groups Next: Irreducible Representations and Character Tables Degenerate Orbitals