Carbon and its Compounds | Class 10 Science Notes

4.2.4 Homologous Series

A homologous series is a group of organic compounds that have the same functional group and similar chemical properties but differ by a CH2 unit in their molecular formula. This section explains that carbon chains can vary in length and branching, and the presence of the same functional group across these compounds results in similar chemical behavior. For example, alcohols like methanol (CH3OH), ethanol (C2H5OH), propanol (C3H7OH), and butanol (C4H9OH) form a homologous series. The difference between successive members is a CH2 group, and their molecular masses increase accordingly. Physical properties such as melting and boiling points show gradual changes with increasing molecular mass, while chemical properties remain similar due to the functional group. The section also discusses the general formulae for alkanes (CnH2n+2), alkenes (CnH2n), and alkynes (CnH2n-2), highlighting the relationship between carbon and hydrogen atoms in these series. An activity encourages students to calculate molecular mass differences and generate homologous series for various functional groups.

📊 Diagram: Table on page 7 (7×4) showing formulae and structures of saturated compounds; Table on page 9 (6×3) listing functional groups; no new figure.

🧪 Activity: Activity 4.2: Calculate differences in formulae and molecular masses of alcohols; arrange alcohols in homologous series; generate series for other functional groups.

🔗 Connection: Prepares for the nomenclature of carbon compounds based on functional groups and chain length.

Table on page 7 (7×4)

Table on page 9 (6×3)