# 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 –ane.

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.

NameMolecular formulaFull structural formula
MethaneCH4Monsters
EthaneC2H6Eat
PropaneC3H8Pupils
ButaneC4H10But
PentaneC5H12Prefer
HexaneC6H14Hairy
HeptaneC7H16Haggis
OctaneC8H18Occasionally

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 –ene 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.

### Step one

Two test tubes of bromine water. An alkane is added to one, an alkene to the other.

### Step two

2 of 3: The test tubes are shaken.

### Step three

3 of 3: The alkane liquid remains orange-brown. The alkene liquid has turned colourless.