Question

What is a homologous series? State any four characteristics of a homologous series.

Answer 1

Hint: Compounds of carbon can be arranged in series of successive compounds showing a gradual change in physical properties of the constituents of the series. Homologous means the same or having a similar relation.

Complete step by step solution:
Let’s see the definition of homologous series:
> A homologous series is a series of hydrocarbons which have similar chemical properties and they share the same general formula. They are organic compounds having similar structure and functional groups. The constituents of the homologous series shoe a gradation in physical properties.
> Some examples of homologous series are:
- Alkane series having general formula ${{C}_{n}}{{H}_{2n+2}}$
\[C{{H}_{4}},\,{{C}_{2}}{{H}_{6}},\,{{C}_{3}}{{H}_{8}},...\]
- Alkene series having general formula ${{C}_{n}}{{H}_{2n}}$
\[{{C}_{2}}{{H}_{4}},\,{{C}_{3}}{{H}_{6}},\,{{C}_{4}}{{H}_{8}},...\]
Four characteristics of a homologous series are:
- They contain the same functional group throughout the series. Like a homologous series of alcohols will contain only OH groups.
- All the members of a homologous series can be represented by the same general formula, like the homologous series of alkanes can be represented by the same formula ${{C}_{n}}{{H}_{2n+2}}$, where n is an integer starting from 1.
- The members of a homologous series have the same chemical properties. This is because they contain the same functional group which determines the chemical properties of an organic compound.
- The members of the homologous series can be prepared by the same general method. They show a gradual increase in the values of physical properties.

Note: Members of a homologous series are called homologous. Two adjacent members differ by one $C{{H}_{2}}$ group. The mass of a higher homologue is greater by 14g than an adjacent lower homologue.