AQA GCSE Chemistry

Revision Notes

7.2.1 Alkenes

Structure & Formula

  • All alkenes contain a double carbon bond, which is shown as two lines between two of the carbon atoms i.e. C=C
  • All alkenes contain a double carbon bond, which is the functional group and is what allows alkenes to react in ways that alkanes cannot
  • The names and structure of the first four alkenes are shown below:

Table Showing the Formulae and Structures of the First Four Alkenes

Alkenes - First 5 members 1 1, downloadable IGCSE & GCSE Chemistry revision notesAlkenes - First 5 members 1 2, downloadable IGCSE & GCSE Chemistry revision notes

  • Compounds that have a C=C double bond are also called unsaturated compounds
  • That means they can make more bonds with other atoms by opening up the C=C bond and allowing incoming atoms to form another single bond with each carbon atom of the functional group
  • Each of these carbon atoms now forms 4 single bonds instead of 1 double and 2 single bonds
  • This makes them much more reactive than alkanes

Double Bond Opening, IGCSE & GCSE Chemistry revision notes

A carbon-carbon double can break and form a single bond, allowing more atoms to attach to the carbon atoms

Exam Tip

The numbers in butene, pentene and hexene refer to the carbon atom in which the C=C begins, counting from the left. E.g. pent-2-ene, C5H10 has the C=C between the 2nd and 3rd carbon atoms. In pent-3-ene the C=C bond is between the 3rd and 4th carbon atoms from the left.

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.

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