Summary:
- There are four types of crystals: (1) ionic, (2) metallic, (3) covalent network, and (4) molecular.
- Properties and several examples of each type are listed in the following table.
- Ionic crystals are hard and brittle and have high melting points.
- Metallic crystals consist of metal cations surrounded by a “sea” of mobile valence electrons.
- Molecular crystals typically consist of molecules at the lattice points of the crystal, held together by relatively weak intermolecular forces.