Formulae & Properties

Specification Point 8.6:
  • Explain an homologous series as a series of compounds which:
    a) have the same general formula
    b) differ by CH2 in molecular formulae from neighbouring compounds
    c) show a gradual variation in physical properties, as exemplified by their boiling points
    d) have similar chemical properties
  • Homologous series are families or groups of organic compounds that have similar features and chemical properties due to them having the same functional group.
  • All members of a homologous series have:
    • The same general formula.
    • The difference in the molecular formula between one member and the next is CH2
    • Gradation in their physical properties.
    • Same functional group.
    • Similar chemical properties.
  • Gradation in the physical properties of a homologous series can be seen in the trend in boiling points of the alkanes.
  • Each alkane has a boiling point that is higher than the one before it.

Homologous series bp table, Edexcel GCSE Chemistry

  • This is more easily seen on a graph:

Alkane Boiling Point, Edexcel GCSE Chemistry

Graph showing gradation in the boiling points of the first 8 alkanes

Edexcel GCSE Chemistry Notes

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Morgan Curtin Chemistry

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.