A homologous series is a series of carbon compounds that have different numbers of carbon atoms but contain the same functional group. It can be represented by the same general formula. Compounds of homologous series differ by CH₂ from their consecutive members. All the compounds of a homologous series show similar chemical and physical properties. For example, alkanes such as methane, ethane, propane, butane, etc. belong to the same homologous series. Similarly, all alkenes belong to a particular homologous series and all alkynes belong to another homologous series.