Covalent bonding has directional characteristics. Because of this, the molecule containing a covalent bond acquires definite geometry. For example, the carbon dioxide molecule is linear with the bond angle equal to 1800, whereas sulphur dioxide is nonlinear with the bond angle equal to 119O. The methane molecule has a tetrahedral geometry with each bond angle equal to 109O 28'. The determination of the molecular geometry of molecules is one of the main interests of chemists. Various methods have been developed to determine molecular parameters including bond distances and bond angles. The main methods amongst them are X-ray diffraction studies on crystals, determination of the dipole moment and heat capacities of molecules, and molecular spectroscopy.