How do functional groups affect the affinity of a molecule for water?

Functional groups influence a molecule's affinity for water through their polarity and ability to form hydrogen bonds. Polar functional groups, such as hydroxyl (-OH) or carboxyl (-COOH), enhance a molecule's hydrophilicity, making it more soluble in water. In contrast, nonpolar groups, like alkyl chains, reduce water affinity, resulting in hydrophobic behavior. Thus, the presence and type of functional groups determine the overall hydrophilicity or hydrophobicity of the molecule.