Welcome to practical physicsPracticle physics - practical activities designed for use in the classroom with 11 to 19 year olds

Finding the size of atoms

The fact that matter is made of particles is perhaps the most powerful idea in science. Understanding the scale of the particles is important. This collection shows how students can estimate the size of molecules and atoms for themselves. 
In a classic experiment, first performed by Lord Rayleigh, a small drop of oil spreads out to form a circular patch on the surface of water. Simple measurements lead to the length of the oil molecule, from which the diameter of carbon atoms can be deduced. 


Change in volume from a liquid to a gas for nitrogen

Simple molecular model of different states of matter

Introducing the oil film experiment

Illustration of oil spreading

Estimating the size of a molecule using an oil film

Dependence of size on method of measurement

Related Guidance

Estimating the size of a molecule using oil