The systematic discussion of molecular symmetry is known as group theory. Group theory is a systematic way of describing the symmetry of molecules using concepts/rules borrowed from mathematics. This tag should be applied to any question which involves the theory or application of point groups, symmetry elements, or character tables.
The systematic discussion of molecular symmetry is known as group theory. Group theory is a systematic way of describing the symmetry of molecules using concepts/rules borrowed from mathematics.
These rules can be applied in a rational, structured way, allowing chemists to quickly determine many properties of molecules.
In chemistry, groups are used to classify crystal structures, regular polyhedra, and the symmetries of molecules. The assigned point groups can then be used to determine physical properties (such as polarity and chirality), spectroscopic properties (particularly useful for Raman spectroscopy, infrared spectroscopy, circular dichroism spectroscopy, magnetic circular dichroism spectroscopy, UV/Vis spectroscopy, and fluorescence spectroscopy), and to construct molecular orbitals.
Applicability of the group-theory tag
- group-theory should be applied to any question which concerns the theory or application of point groups, symmetry elements, or character tables (i.e. any question that considers symmetry in a systematic way).
- The group-theory tag should not be applied to all questions relating to symmetry/geometry of molecules in a more general sense. Consider 'why does methane belong to the Td group?' vs 'why does methane have tetrahedral geometry?'. Clearly the tetrahedral point group is involved in both questions, however in the later, it is clear that molecular geometry is being discussed rather than any actual interest in the point group itself.
- group-theory is permissible by itself, however, many questions currently tagged with group-theory ask about applications of group theory, and as such additional tags should be used to further identify the question.
The following tags are related to group-theory, with multiple questions on chemistry.se already tagged with one of more of the following which may be useful as additional tags on questions identified as being related to group theory:
- @Orthocresol's MathJax Character Tables, hosted on meta.chem.se.
Group theory is a well developed area of chemistry, and many books have been published on the topic, ranging from simple qualitative introductions to math-heavy derivations. Some good examples are listed below, however any good physical chemistry textbook, and many inorganic textbooks will also devote a chapter to chemical group theory.
Kettle, S.; Symmetry and Structure, a readable group theory for chemists, Wiley: Sussex, 2007. An easy introduction to group theory, focusing on applications and qualitative description.
Cotton, F. A.; Chemical Applications of Group Theory, John Wiley & sons inc.: New York, 1990. An older book covering a lot of topics, less readable and more math-heavy, but a good reference for more advanced topics such as MO theory.