There are several main types of atomic models in use today: two of the most common are 'ball and spoke' and 'space-filling' types; each is useful for displaying different information about the molecules. Whilst ball and spoke models are designed to show how the atoms are bonded together, space-filling models accurately demonstrate the size and shape of the molecule.
Most sets of models differentiate between different types of atoms using colours, whilst some vary the size of the atoms, often to allow visually impaired people to use the sets.
Read more: types of molecular models
What colour is an atom?
We don't think about single atoms of elements as having a colour. It is only on a much bigger scale that solids (and some liquids and gases) display colours. The colours used in modelling kits are chosen for identification purposes and do not correspond to any actual colour in the atoms. Although oxygen atoms are coloured red in kits, liquid oxygen is actually blue in colour.
There are several conventions for the colours of molecular models. Many use the colour scheme shown in the table below, which was recommended by the Institute of Physics.(1) Models using this scheme include the plastic space-filling models developed by Corey and Pauling, and later improved on by Kultun (known as CPK models). Not all models use this convention though; in the Griffin and George model set, the colours were chosen on the basis of how clearly they would show up in black and white photographs.
The Institute of Physics recommended colour scheme for molecular models
Element |
Atom colour |
| carbon | black |
| hydrogen | white or cream |
| oxygen | red |
| nitrogen | blue |
| fluorine | yellowish green |
| chlorine | light green |
| bromine | mid-green |
| iodine | dark green |
| sulphur | yellow |
| phosphorus | purple |
References
- Institute of Physics, 'The standardisation of crystal structure models', Journal of Scientific Instruments, Vol. 24, no. 9 (1947), 249-250.
Further reading
- A. Walton, Molecular & Crystal Structure Models (Chichester: Ellis Horwood Limited, 1978).
- E. Francoeur, 'The forgotten tool: the design and use of molecular models', Social Studies of Science, Vol. 27, No. 1 (1997), 7-40.
Ruth Horry
Ruth Horry, 'Modelling chemistry', Explore Whipple Collections, Whipple Museum of the History of Science, University of Cambridge, 2008.