Quick Notes Carbon Chains
- Prefixes are used when naming organic molecules to show how many carbon atoms are bonded together successively (in a ‘chain’).
- meth = 1 carbon, eth = 2 carbons, pro = 3 carbons, but = 4 carbons, pent = 5 carbons, hex = 6 carbons, hept = 7 carbons, oct = 8 carbons, non = 9 carbons, dec = 10 carbons
- Hydrocarbons are molecules made up of only carbon and hydrogen atoms.
- Alkanes have single bonds between each carbon atom, all other available bonds are made to hydrogen atoms – they are called ‘saturated’ hydrocarbons.
- Alkenes have a double bond between two of their carbon atoms – they are called ‘unsaturated’ hydrocarbons.
- Alkly groups are carbon chain groups bonded to another carbon chain.
Full Notes Carbon Chains
Within organic molecules, carbon atoms can be bonded to other carbon atoms. This creates a ‘chain’ of carbon within a molecule. The properties of an organic molecule can alter depending on the size of this chain, so it’s important to be able to recognise and name the carbon chain present within an organic molecule.
If there are only carbon and hydrogen atoms in a molecule, it’s called a hydrocarbon. When the carbon atoms are all bonded with single carbon-carbon bonds, it’s called an alkane.
We name alkanes based on the length of the carbon chain. The prefix (start!) of the name is unique to the carbon chain and the suffix (end!) of the name is simply –ane. The -ane just tells us that the molecule is an alkane. The suffix can and does change depending on what else is bonded to the chain.
1 carbon = meth-
2 carbons = eth-
3 carbons = prop-
4 carbons = but-
5 carbons = pent-
6 carbons = hex-
7 carbons = hept-
8 carbons = oct-
9 carbons = non-
10 carbons = dec-
Most A-level specifications require you to know and memorise the prefix for molecules containing up to 10 carbons.
For alkanes, each carbon atom is bonded to another carbon atom and any remaining available bonds are made to hydrogen atoms. The alkane is described as a ‘saturated’.
If there is a double bond between two carbon atoms within the molecule, the hydrocarbon becomes an alkene and is described as ‘un-saturated’.
A carbon chain group bonded to another carbon chain is called an alkyl group and follows the same prefix as usual.