Assigning each molecule a point group classifies molecules into categories with similar symmetry properties. For example, PCl 3, POF 3, XeO 3, and NH 3 all share identical symmetry operations. They all can undergo the identity operation E, two different C 3 rotation operations, and three different σ v plane reflections without altering their identities, so they are placed in one point group, C 3v, with order 6. Similarly, water (H 2 O) and hydrogen sulfide (H 2 S) also share identical symmetry operations. They both undergo the identity operation E, one C 2 rotation, and two σ v reflections without altering their identities, so they are both placed in one point group, C 2v, with order 4. This classification system helps scientists to study molecules more efficiently, since chemically related molecules in the same point group tend to exhibit similar bonding schemes, molecular bonding diagrams, and spectroscopic properties. Point group symmetry describes the symmetry of a molecule when fixed at its equilibrium configuration in a particular electronic state. It does not allow for tunneling between minima nor for the change in shape that can come about from the centrifugal distortion effects of molecular rotation.