Why are homologous series of carbon compounds so called? Write chemical formula of two consecutive members of a homologous series and state the part of these compounds that determines their (i) physical properties, and (ii) chemical properties.

Explanation

All the organic compounds having similar structures show similar properties and theyare put together in the same groups of series called homologous series.
For example, all the alkanes have similar structures with single covalent bonds and show similar chemical properties so they are grouped together in a homologous series having general formula `C_(n)H_(2n+2).`
The two consecutive members of a homologous series are methane `CH_(4)` and ethane `C_(2)H_(6)`.
(i) Any two adjacent homologues differ by 1 carbon and 2 hydrogen atoms in their molecualr formulae. So the difference in molecular masses of any two adjacent homologues is 14 u. Thus the members of a homologous series show a gradual change in their physical properties with increas in molecular mass.
(ii) All the compounds of a homologous series show similar chemical properties because they have similar structures and similar bonding.