Homologous Series & Functional Groups (Edexcel A Level Chemistry)

Homologous series

• A homologous series is a group of organic compounds that have the same functional group, but each successive member differs by CH₂

Ethanol and propanol belong to the same homologous series

Homologous Series of Alkanes

• Things we can say about a homologous series:
  • Each member has the same functional group
  • Each member has the same general formula
  • Each member has similar chemical properties
  • Each successive member differs by  -CH₂ –
  • Members have gradually changing physical properties, for example, boiling point, melting point and density
• As a homologous series is ascended, the size of the molecule increases
• This has an effect on the physical properties, such as boiling point and density

Functional Groups

• Functional groups determine the physical and chemical properties of molecules
• The table below shows a summary of common functional groups found in compounds
• R is any other atom or group of atoms (except for hydrogen)

Functional Groups found in Compounds Table