What is Homologous series? Explain with an example.

A homologous series is a series of organic compounds which belong to the same family (i.e. possess same functional group) and show similar chemical properties. The members of this series are called homologue and differ from each other by the number of CH₂ units in the main carbon chain. Following are the characteristics of a homologous series

• All homologues of a series have the same general formula e.g., all alkanes have the general formula C_n H_{2n + 2}, alkyl halides have the general formula C_nH_(2n+1)X, alkenes have the general formula C_nH_2n etc.
• Each consecutive member differs from the next by one carbon atom and two hydrogen atoms (-CH₂ group).
• The difference in the molecular mass between two consecutive homologues is 14 amu.
• The physical properties of homologues show a regular gradation.
• Homologues of a series have similar chemical properties.