Homologous series

A series of organic molecules which contain the same reactive part of the molecule (called the functional group), but a different carbon skeleton. The molecules within the series have very similar chemical properties, but gradually changing physical properties (like solubility and melting point). For example, the alcohols:

CH₃OH, CH₃CH₂OH, CH₃CH₂CH₂OH, CH₃CH₂CH₂CH₂OH...

and the carboxylic acids:

HCOOH, CH₃COOH, CH₃CH₂COOH, CH₃CH₂CH₂COOH...