Question

Methane belongs to the homologous series of alkanes.
A ) True
B ) False

Answer 1

Homologous series contains compounds having similar chemical properties and same functional groups. Successive members of homologous series differ by a methylene group.

Complete step by step answer:
Organic compounds with the same general formula have carbon atoms of varying length. A series of compounds can be formed in which the general formula is the same and the individual members (organic compounds ) of the series differ by a repeating unit. Such a series is called a homologous series.

Alkanes form a homologous series. The general formula of alkanes is ${{\text{C}}_n}{{\text{H}}_{2n + 2}}$. Here, n represents the number of carbon atoms. In the homologous series of alkanes, the repeating unit is a methylene group. The methylene group is represented by the formula ${\text{C}}{{\text{H}}_2}$. Methane is the first member of alkane homologous series. The chemical formula of methane is ${\text{C}}{{\text{H}}_4}$. When n is 1, the chemical formula of methane is obtained.
${{\text{C}}_n}{{\text{H}}_{2n + 2}} = {{\text{C}}_1}{{\text{H}}_{2\left( 1 \right) + 2}} = {\text{C}}{{\text{H}}_4}$
Ethane is the second member of the alkane homologous series. The chemical formula of ethane is ${{\text{C}}_2}{{\text{H}}_6}$. When n is 2, the chemical formula of ethane is obtained.
${{\text{C}}_n}{{\text{H}}_{2n + 2}} = {{\text{C}}_2}{{\text{H}}_{2\left( 2 \right) + 2}} = {{\text{C}}_2}{{\text{H}}_6}$
Propane is the third member of the alkane homologous series. The chemical formula of propane is ${{\text{C}}_3}{{\text{H}}_8}$. When n is 3, the chemical formula of propane is obtained.
${{\text{C}}_n}{{\text{H}}_{2n + 2}} = {{\text{C}}_3}{{\text{H}}_{2\left( 3 \right) + 2}} = {{\text{C}}_3}{{\text{H}}_8}$

The molecular formula of methane, ethane, propane, butane, pentane and hexane are shown below.
${\text{C}}{{\text{H}}_4},{\text{ }}{{\text{C}}_2}{{\text{H}}_6},{\text{ }}{{\text{C}}_3}{{\text{H}}_8},{\text{ }}{{\text{C}}_4}{{\text{H}}_{10}}{\text{,}}{{\text{C}}_5}{{\text{H}}_{12}}{\text{,}}{{\text{C}}_6}{{\text{H}}_{14}}$

The structural formula of methane, ethane, propane, butane, pentane and hexane are shown below.

$${\text{C}}{{\text{H}}_4},{\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_3},{\text{ C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_3},{\text{ C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_3}{\text{, }} \\\ {\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_3}{\text{, C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_3} \\\$$

From the above structural formulae, you can conclude that each successive member of the alkane homologous family has one additional methylene $\left( {{\text{C}}{{\text{H}}_2}} \right)$ group.

Methane belongs to the homologous series of alkanes.
Hence, the given statement is true

So, the correct answer is “Option A”.

Note: Alkenes form a homologous series. The general formula of alkenes is ${{\text{C}}_n}{{\text{H}}_{2n}}$.
Alkynes form a homologous series. The general formula of alkynes is ${{\text{C}}_n}{{\text{H}}_{2n - 2}}$.