High-speed footage of a hammer shattering a clump of copper (II) sulfate crystals. This demonstrates the brittleness of ionic compounds. Ionic compounds are those made up of ions, positively and negatively charged atoms or groups. The main force holding the material together is electrostatic, between neighbouring ions with opposite charge. This is a strong force that resists deformation, and also gives such compounds a high melting point. However, the lack of ability to deform means that when stress is applied, they either resist it, or the charges move out of alignment and the material deforms suddenly and catastrophically, as seen here.