Modelling molecules

3D constructional models

A ball and stick model can be used to show the structure of a simple molecule. This type of model has the advantage of showing how the atoms are connected and how they are arranged in space, including the angles between bonds.

A photo of a ball and stick model of ethane.
A ball and stick model of ethane

An alternative 3D model, often used in computer simulations, is a space-filled model. This has the disadvantage that it is no longer possible to see the angles between bonds. The main advantage is that it shows the overlap of the electron shells of the atoms.

A photo of a space-filled model of ethane.
A space-filled model of ethane

Displayed formula

You can represent a simple molecule by drawing its structure. In these structures:

  • show each atom by its element symbol
  • show each covalent bond as a straight line
  • show each double bond as two straight lines
Two letter Hs connected by a line

For example, a hydrogen molecule has two H atoms and one covalent bond. The diagram shows its structure.

A carbon dioxide molecule has one carbon atom that is connected to two oxygen atoms via double bonds.


The advantage of a displayed formula, compared with a molecular formula, is that it shows how the atoms are connected. The disadvantage is that it does not show how the atoms are arranged in 3D space.