4.23 Meet the alkenes
The Alkenes are another Homologous series of Hydrocarbons. They differ from the Alkanes because they contain in their molecules at least one double bond between two of the carbon atoms.
Because of their double bonds, the alkenes are more reactive than the alkanes and thus they are useful for making new compounds. Alkenes can be made into polymers - such as polyethene and polystyrene - synthetic materials which have a wide variety of uses.
This video shows the steam distillation of limonene from orange peel. Steam distillation is used to avoid the limonene becoming too hot.
4.23 - 4.24 Activity 1.Find the formula
Ethene is the simplest unsaturated hydrocarbon (Alkene)
Students should:
- 4.23 know that alkenes contain the functional group C=C
- 4.24 know the general formula for alkenes
4.25 Activity 2. What's unsaturated?
Students should:
- 4.25 explain why alkenes are classified as unsaturated hydrocarbons
For a molecule to be saturated it must have the maximum possible number of Hydrogen atoms on it. Butene's double bond means that it does not have the maximum number of Hydrogen atoms. This means that butene is unsaturated.
Since butane has the maximum number of Hydrogen atoms, it is a saturated molecule.
Unsaturated means there is a C=C functional group present.
4.25 Activity 3. Healthy options
4.26 Activity 4. Name ene and draw ene!
Students should:
- 4.26 understand how to draw the structural and displayed formulae for alkenes with up to four carbon atoms in the molecule, and name the unbranched-chain isomers
4.27 Activity 5. Alkenes with bromine
Students should:
- 4.27 describe the reactions of alkenes with bromine to produce dibromoalkanes
- 4.28 describe how bromine water can be used to distinguish between an alkane and an alkene