Write a note on homologous series.

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Homologous series:

A series of compounds of the same family in which each member has the same type of carbon skeleton and functional group, and differs from the next member by a constant difference of one methylene group (-CH₂ -) in its molecular and structural formula is called as homologous series.
The individual members of the series are called homologues and they can be represented by a same general formula.
Two successive homologues differ by one – CH² (methylene) unit (i.e., molecular weight of each successive member differs by 14 units).
Homologues show similar chemical properties.
Physical properties (like melting point, boiling point, density, solubility, etc.) of the homologues show a gradual change with increase in the molecular weight of the member.

Note: Consider the homologous series of straight chain aldehydes. The boiling point increases down the series as molecular weight increases.

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