It is the maximum distance upto which a molecule can exert some appreciable force of attraction on other molecules. It is of the order of 10″ 9 m in solids and liquids.
Sphere of influence. A sphere drawn around a molecule as centre and with a radius equal to the molecular range is called the sphere of influence of the molecule. The molecule at the centre attracts all the molecules lying in its sphere of influence.
While studying the behaviour of a molecule under the influence of cohesive forces, we need to consider only the molecules lying in its sphere of influence.
Surface film:
A thin film of liquid near its surface having thickness equal to the molecular range for that liquid is called surface film.