Hydrocarbons are molecules containing only carbon and hydrogen, they are named according to the number of carbons present.

A homologous series is a group of hydrocarbons which all have the same general formula, an example of this is all alkanes have the general formula CnH2n+2 where 'n' is the number of carbons in the chain. Physical properties of molecules change up a homologous series.

When all carbon atoms are bonded to four different atoms, a molecule is considered saturated. Sometimes a carbon atom is only bonded to three different molecules and a double bond forms between two carbon atoms, this is an unsaturated molecule.

Isomers are compounds with the same molecular formula but different structural formulae, meaning they have the same atoms but are arranged differently.