Many of the chemicals of life contain components called functional groups. These small molecules, consisting of only a few atoms, are quite common; indeed, most organic compounds have one or more. For instance, the illustration that introduces this WebModule is of an amino acid. It, like all amino acids, has two functional groups, an amine and a carboxyl. In some respects, functional groups behave like atoms. They tend to be passed from molecule to molecule relatively unaltered. Unlike atoms, their behavior in a molecule is consistent. They give molecules their characteristic properties. For instance, any molecule containing the hydroxyl group (-OH) is readily soluble in water, while those containing the methyl group (-CH3) are insoluble. In this WebModule, which is really an exercise, you will learn about the structure and occurrence of functional groups.