AQA GCSE Chemistry 8462
Atomic Structure and the Periodic Table
Bonding, Structure, and the Properties of Matter
Chemical Analysis
Chemical Changes
Chemistry of the Atmosphere
Energy Changes
Organic Chemistry
Quantitative Chemistry
The Rate and Extent of Chemical Change
Using Resources
Organic Chemistry
Structure and formulae of alkenes
- 3 things to know
- Paper 2
Overview
Alkenes as hydrocarbons with a carbon–carbon double bond, their general formula CₙH₂ₙ, unsaturated alkenes and saturated alkanes, the first four alkenes and their formulae, why ethene is the smallest alkene, and telling an alkene from an alkane by its formula.
What you need to know
Answer each one before you reveal it.
State the general formula of the alkenes.
Propane is C₃H₈. Compare the formula of propene with it.
Questions from this subtopic
Each one with the model answer underneath.
- 1
What feature of its structure makes a hydrocarbon an alkene?
Model answer
It contains a carbon–carbon double bond.
- 2
State the general formula of the alkenes.
Model answer
The general formula of the alkenes is CₙH₂ₙ.
- 3
Use the general formula of the alkenes to give the molecular formula of the alkene with four carbon atoms.
Model answer
C₄H₈.
- 4
An alkene molecule contains 10 hydrogen atoms. How many carbon atoms does it contain?
Model answer
Five.
- 5
What does it mean to say that an alkene is unsaturated?
Model answer
It contains a carbon–carbon double bond, so it does not hold the maximum possible number of hydrogen atoms.
- 6
How many fewer hydrogen atoms does an alkene have than the alkane with the same number of carbon atoms?
Model answer
Two fewer.
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