Homologous Series (Cambridge (CIE) IGCSE Combined Science): Revision Note

Homologous series

Extended tier only

• A homologous series is a family of organic compounds with similar chemical properties

• This is because all members of a homologous series contain the same functional group

  • The functional group is a group of atoms bonded in a specific arrangement that is responsible for the characteristic reactions of the series

Table of compounds & their functional groups

General characteristics of a homologous series

• All members of a homologous series have the same general formula

  • This means that each member differs from the next by a CH₂ unit

• They also show a trend in physical properties

  • For example, as the molecules get larger:

    • Boiling point increases

    • Melting point increases

    • Viscosity increases