There are 7 basic symmetry operations that can account for all molecular symmetries. We define an operation based on observation that the molecule appears unchanged after the operation. However, if we labeled the atoms we would see that they have been moved by the operation. These basic symmetry operations are:
The symmetry operations can be applied to molecules in order to determine the collection of appropriate symmetry operations that correspond to the molecular symmetry. Such a collection is known as a group. In the next section we define a group. Then we show how to assign a molecule to a point group. Finally, we proceed to applications in which the point group forms the basis for construction of molecular orbitals in electronic structure theory and vibrational normal modes. Based on the insight from applications that include the interaction of electromagnetic radiation in the description the point group can be used to predict allowed and forbidden electronic transitions,infrared and Raman active modes and numerous other properties.
