. Why homologous series of carbon compounds are 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.
Ans. All the organic compounds having similar structures show similar properties and they are put together in the same groups or 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 CnH2n+2 .
• The two consecutive members of a homologous series are methane CH4 and ethane
(i) Any two adjacent homologues differ by 1carbon and 2 hydrogen atoms in their molecular 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 increase in molecular mass.
(ii) All the compounds of a homologous series show similar chemical properties because they have similar structures and similar bonding.