Chapter 12 · Liquids, Solids, and Intermolecular Forces
12.7Types of Crystalline Solids
10 min · two checks
Predict
What holds a crystal of solid argon together, compared with a crystal of sodium chloride?
The idea
- Classify solids as molecular, ionic, or atomic (including metallic and network).
- Match melting point to the force that is broken.
Molecular solids are lattices of molecules. Ice, dry ice, and sugar are examples. Melting them separates molecules; it does not break the covalent bonds inside. Melting points are relatively low. Ionic solids are lattices of ions. Melting them means prying ions apart, which takes much more energy. They are brittle and, when melted or dissolved, they conduct.
Atomic solids have atoms at the lattice points. Metallic solids conduct because valence electrons are shared across the metal. Network covalent solids — diamond, quartz — are one giant molecule of covalent bonds. Melting a network solid means breaking covalent bonds, so the melting points are enormous. Classify the solid before you predict the melting point. “It contains oxygen” does not tell you whether you are melting ice or quartz.
Keep these
- Molecular: weak intermolecular forces, low melting points.
- Ionic: high melting points, brittle, conduct when melted.
- Network covalent: covalent bonds throughout, very high melting points. Metals conduct as solids.