Intermolecular and Surface Forces, 3rd Edition

4 Interactions Involving Polar Molecules

4.1 What Are Polar Molecules?

Most molecules carry no net charge, but many possess an electric dipole. For example, in the HCl molecule the chlorine atom tends to draw the hydrogen’s electron toward itself, and this molecule therefore has a permanent dipole. Such molecules are called dipolar or simply polar molecules. The dipoles of some molecules depend on their environment and can change substantially when they are transferred from one medium to another, especially when molecules become ionized in a solvent. For example, the amino acid molecule glycine contains an acidic group on one side and a basic group on the other. In water at neutral pH, the NH₂ group acquires a proton and the OH group loses ...