Alkanes and alkenes
There are two different sub-sets of hydrocarbons: alkanes and alkenes.
Alkanes
The alkanes are a subset of hydrocarbons whose names all end in 鈥揳ne.
The names, molecular formulae and the structural formulae of the first eight alkanes must be learned. Using a mnemonic can make learning the names easier.
| Name | Molecular formula | Full structural formula |
| Methane | CH4 | Monsters |
| Ethane | C2H6 | Eat |
| Propane | C3H8 | Pupils |
| Butane | C4H10 | But |
| Pentane | C5H12 | Prefer |
| Hexane | C6H14 | Hairy |
| Heptane | C7H16 | Haggis |
| Octane | C8H18 | Occasionally |
| Name | Methane |
|---|---|
| Molecular formula | CH4 |
| Full structural formula | Monsters |
| Name | Ethane |
|---|---|
| Molecular formula | C2H6 |
| Full structural formula | Eat |
| Name | Propane |
|---|---|
| Molecular formula | C3H8 |
| Full structural formula | Pupils |
| Name | Butane |
|---|---|
| Molecular formula | C4H10 |
| Full structural formula | But |
| Name | Pentane |
|---|---|
| Molecular formula | C5H12 |
| Full structural formula | Prefer |
| Name | Hexane |
|---|---|
| Molecular formula | C6H14 |
| Full structural formula | Hairy |
| Name | Heptane |
|---|---|
| Molecular formula | C7H16 |
| Full structural formula | Haggis |
| Name | Octane |
|---|---|
| Molecular formula | C8H18 |
| Full structural formula | Occasionally |
Alkanes contain more than double the number of hydrogen atoms than carbon atoms. To calculate how many hydrogen atoms an alkane has, double the number of carbons and add two. The general formula of the alkanes is \({C_n}{H_{2n + 2}}\).
Alkenes
The second subset of hydrocarbons is called the alkenes. Their names all end in 鈥揺ne for example ethene.
Alkenes all contain a carbon to carbon double bond which makes them more reactive than the alkanes.
Alkenes contain twice as many hydrogen atoms as carbon atoms. The alkenes have the general formula \({C_n}{H_{2n}}\).
Alkenes are more reactive than alkanes because they have a double bond.