Molecular point group

Molecular point group is a classification that helps group similar chemical molecules together based on their symmetry properties. Given the rapid increase of discovered chemical molecules, chemists saw the need to develop a classification scheme that would categorize molecules into groups of similar properties. Since molecular symmetry plays a central role in the field of inorganic chemistry, it was proposed that the molecular classification would be based on molecular symmetry. In other words, molecules that undergo the same symmetry operations without changing their identities would be grouped together. This choice of classifying molecules can be understood by the fact that molecular symmetry is used extensively to determine molecular orbitals, vibrations, and other molecular properties. therefore, molecules that share the same symmetry operations tend to have similar molecular and vibrational properties, such as moleuclar orbital diagrams.

Overview

Given that symmetry is an obvious way to classify molecules, scientists developed a scheme based on what symmetry operations a molecules can undergo without changing its identities. For example, PCl₃, POF₃, XeO₃, and NH₃ all share identical symmetry operations.^[1] They all can undergo E, two different C₃, and three different σ_v planes without altering their identities Therefore, observing that all four molecules are symmetry-similar, they are placed in one point group, C_3v to be shown later.^[2] Similarly, water, H₂O, and Hydrogen sulfide, H₂S, also share identical symmetry operations. They all undergo E, one C₂, and two σ_v planes without altering their identities.^[3] Therefore, they are both placed in one point group, C_2v to be shown later.

Determining point groups

A molecule's point group can be determined from the symmetry operations that the molecule can undergo without changing its identity. A list of common point groups is found in the article on molecular symmetry. A flow chart can be used to easily determine a molecule's point group without the need to figure out all symmetry operations.

References

^ Pfennig, Brian. Principles of Inorganic Chemistry. Wiley. p. 191. ISBN 978-1-118-85910-0.
^ pfennig, Brian. Principles of Inorganic Chemistry. Wiley. ISBN 978-1-118-85910-0.
^ Miessler, Gary. Inorganic Chemistry. Pearson. ISBN 9780321811059.

[1] Pfennig, Brian. Principles of Inorganic Chemistry. Wiley. p. 191. ISBN 978-1-118-85910-0.

[2] , Brian. Principles of Inorganic Chemistry. Wiley. ISBN 978-1-118-85910-0.

[3] Miessler, Gary. Inorganic Chemistry. Pearson. ISBN 9780321811059.

[1]

[2]

[3]