Homologous Series

Specification Point 9.32C:
  • Recall members of a given homologous series have similar reactions because their molecules contain the same functional group and use this to predict the products of other members of these series
  • 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.
  • The chemistry of homologous series is therefore determined by the functional group.
  • We can use this to predict how molecules further down a homologous series will react.
  • For example we know that ethene will decolourise bromine water, so we can predict that hexene and septene will do the same, even though they are bigger molecules.
  • This is due the the alkene functional group, the C=C double bond, which is present in all alkenes.

Need help?

Edexcel GCSE Chemistry Notes

Want to aim for a Level 9?

See if you’ve got what it takes. Test yourself with our topic questions.

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.