More about fractions


Crude oil is mostly made up of a group of hydrocarbons called the alkanes.

A homologous series is a series of molecules which:

The table shows four alkanes, their molecular formula, displayed formula and ball-and-stick model diagram.

Table showing four alkanes, their molecule formulae and their structures

General formula

The formula of any alkane can be worked out using the general formula CnH2n+2 where n = the number of carbon atoms.

For example, for a hydrocarbon with ten carbon atoms:

  • n = 10 and 2n+2 = 22
  • the formula is C10H22

Work out the formula for a hydrocarbon molecule with 6 carbon atoms.