Alkanes and Alkenes
- Hydrocarbons that contain single bonds only are called alkanes.
- Hydrocarbons that have at least two carbon atoms joined together by a double bond are called alkenes.
Displayed formula of alkanes
Bromine water is an orange solution of bromine. It becomes colourless when shaken with an alkene. Alkenes can decolourise bromine water, while alkanes cannot.
Polymer displayed formula
Polymer molecules are very large compared with most other molecules, so the idea of a repeating unit is used when drawing a displayed formula. When drawing one, starting with the monomer:
- change the double bond in the monomer to a single bond in the repeating unit
- add a bond to each end of the repeating unit.
What does polymerisation need?
- High pressure
Saturated and unsaturated
Alkanes are saturated - they have only single bonds.
Alkenes have a double bond - they are unsaturated.
Displayed formula of saturated hydrocarbons
Lots of unsaturated monomer molecules (alkenes) can open up their double bonds and join together to form polymer chains