Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. They determine the properties and behaviors of organic compounds, such as alcohols, carboxylic acids, and amines. Each functional group has a unique structure and reactivity, which helps chemists predict how different substances will interact. For example, the hydroxyl group (-OH) is a functional group found in alcohols, making them polar and able to form hydrogen bonds. This property influences their solubility in water. Understanding functional groups is essential for studying organic chemistry and designing new compounds in fields like pharmaceuticals and materials science.