Homologous Series (Cambridge International IGCSE Science)

Spec point — C12.2.1

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

Exam Hint Make sure you can identify the functional group for each homologous series.

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

Exam Hint Be careful with your language for homologous series:

• SAME

  • The same functional group
  • The same general formula

• SIMILAR

  • Similar chemical properties, e.g. similar types of reactions

• TREND

  • A trend in physical properties, e.g. melting point