Upon completion of this module, you should be able to understand the differences in bonding between metallic, ionic, and covalent crystals and understand the differences between unit cells of metallic, ionic, and covalent crystals. Crystals can be classified as metallic, ionic, or covalent. The classification is dependent upon the type of bonding that the crystal exhibits. Metallic crystals, known as metals, consist entirely of metal atoms and may possess a primitive, body-centered, or face-centered cubic lattice. The delocalization of valence electrons characterizes bonding in metallic crystals.