Question

What is the difference in the molecular formula of any two adjacent homologs in terms of :

The number and kind of atoms per molecule

Answer 1

Definition of homologous series

• Homologous series is a series of compounds with very similar chemical properties and functional groups differing from the successive member by ${\mathrm{CH}}_2$.
• Carbon chains having varying lengths have a general formula.
• These series are common in organic compounds.

For example series of alkanes whose general formula of the compound is ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}+2}$ and the compounds are methane ${\mathrm{CH}}_4$ethane ${\mathrm{C}}_2{\mathrm{H}}_6$ propane ${\mathrm{C}}_3{\mathrm{H}}_8$ and butane ${\mathrm{C}}_4{\mathrm{H}}_{10}$
Therefore, the difference in the molecular formula of any two adjacent homologs is: ${\mathrm{CH}}_2=$$12+2\times 1=14amu$ in terms of molecular mass.
The number and kind of atoms per molecule are one carbon and two hydrogens. (${\mathrm{CH}}_2$)