What is here?

Hydrocarbons are compounds containing hydrogen and carbon atoms only. The alkanes are a homologous series of hydrocarbons with the general formula CnH2n+2.

The models show the first four unbranched members of this series. You can also see the structural and displayed formulae for these alkanes.

Use your mouse (or finger on touch devices) to move or scale molecules. Double tap to stop and start each animation.

atom labels
ball and stick model
space-filling model
perspective view

methane, CH4

ethane, C2H6

propane, C3H8

butane, C4H10

Homologous series

A homologous series is a series of compounds which:

  • have the same functional group
  • have the same general formula
  • differ by CH2 in molecular formulae from neighbouring compounds
  • show a gradual variation in physical properties, such as their boiling points
  • have similar chemical properties.

Functional groups

A functional group is an atom, group of atoms or a bond responsible for the characteristic chemical reactions of a substance. The functional group in alkanes is most easily shown as —CH3.

General formulae

A general formula is a chemical formula used to represent the members of a homologous series. The general formula for the alkanes is CnH2n+2.

Hexane molecules, for example, contain six carbon atoms:

n = 6
2n + 2 = (2 × 6) + 2 = 14

So the molecular formula for hexane is C6H14.

Structural and displayed formulae

A structural formula shows the number of atoms of each element in a molecule, and their positions in the molecule.

A displayed formula shows the same information as a structural formula, but in addition it shows the bonds between the atoms.

Name of alkaneStructural formulaDisplayed formula