1. Solids  Ionic Crystals  Strength of attractive forces in ionic crystals is indicated by Coulomb’s law,  F = q 1 q 2 /r  Forces tend to be very large  Crystals are very rigid and brittle

2. Solids  Molecular Crystals  Composed of either atoms of nonmetals or of covalent molecules  Held together by London forces, dipole- dipole attractions, hydrogen bonding or a mixture of the 3 (weak forces).  Tend to be soft crystals, with low MP

3. Solids  Network (Covalent) Crystals  Has a lattice structure in which the atoms are covalently bonded to each other  Result is one large molecule with a continuous network of covalent bonds.  Ex. Diamond, silicon dioxide, silicon carbide, graphite In diamond- each C atom is covalently bonded to 4 other C atoms in a tetrahedral (sp 3 ) geometry. In graphite, each C atom is covalently bonded to 3 other C atoms in a trigonal planar (sp 2 ) geometry. The extra p e - that isn’t used in bonding holds the sheets weakly together, allowing them to slide. Silicon carbide

4. Solids  Amorphous (noncrystalline) solids  Do not have a distinct, sharp MP. They soften gradually over a large temp. range  Examples are glass and many plastics