Dancing Crystals: A Dramatic Illustration of Intermolecular Forces

Crystals of naphthalene form on the surface of an acetone solution and dance about in an animated fashion illustrating surface tension, crystallization, and intermolecular forces. Additional experiments reveal the properties of the solution. Flows within the solutions can be visualized by various means. Previous demonstrations of surface motion are explored and compared with the dancing crystals. London, dipole–induced dipole, and dipole–dipole forces are discussed. This demonstration can be used for discussion of intermolecular forces, properties of liquids, surface tension, Marangoni effects, crystallization, solubility, and heat of solution. Video presentations are also available for this article.