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Chemical Analysis, Organic Chemistry and Materials

Alkenes and why they are unsaturated

  • 2 things to know
  • Paper 2

Overview

The formulae of ethene, propene and butene, the general formula CₙH₂ₙ, the structures of but-1-ene and but-2-ene, the C=C functional group, and why alkenes are unsaturated.

What you need to know

Answer each one before you reveal it.

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Key term

What is the general formula of the alkenes?

Key term

In a molecule of ethene, how many hydrogen atoms are joined to each carbon atom, and what joins the two carbon atoms?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Give the formula of a molecule of ethene.

    Model answer

    C₂H₄.

  2. 2

    Give the formula of a molecule of propene.

    Model answer

    C₃H₆.

  3. 3

    Give the formula of a molecule of butene.

    Model answer

    C₄H₈.

  4. 4

    What is the general formula of the alkenes?

    Model answer

    CₙH₂ₙ, so propene with three carbon atoms has six hydrogen atoms.

  5. 5

    In a molecule of ethene, how many hydrogen atoms are joined to each carbon atom, and what joins the two carbon atoms?

    Model answer

    Two hydrogen atoms are joined to each carbon atom, and the carbon atoms are joined to each other by a double bond.

  6. 6

    How do the structures of but-1-ene and but-2-ene differ?

    Model answer

    But-1-ene has its double bond between the first and second carbon atoms, while but-2-ene has it between the second and third.

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