The purpose of learning group theory is that molecular symmetry can be applied to understand the properties of molecules. This chapter introduces two applications of symmetry: chirality and molecular vibrations (in the context of analyzing IR and Raman spectra). An additional application of symmetry, to understand molecular bonding, deserves its own chapter and will be explored in Chapter 5. 2.4.1: Molecular Vibrations Symmetry and group theory can be applied to understand molecular vibrations. This is particularly useful in the contexts of predicting the number of peaks expected in the infrared (IR) and Raman spectra of a given compound. We will use water as a case study to illustrate how group theory is used to predict the number of peaks in IR and Raman spectra. 2.4.2: Chirality