1. Crystal structures

2. Sodium chloride (Giant) ionic crystal Face centred cubic
High mp – lots of energy needed to break many strong ionic bonds to separate ions.
Conduct electricity when molten or aqueous – ions are free to move and carry the current.
Brittle -

3. magnesium (Giant) metallic crystal Hexagonal close packed.
Conducts heat and electricity (delocalised electrons from outer shell of atoms can move).
Malleable and ductile (delocalised electrons allow layers to slide over each other) – after small distortion, each metal ion is in same environment so new shape is retained.

4. diamond Face Giant covalent/macromolecular crystal
Each carbon covalently bonded to four others in tetrahedral arrangement [bond angle 109.5o]
Very hard
Very high mp – lots of energy needed to break many strong covalent bonds
Electrical insulator – no free charged particles to carry current

5. graphite Giant covalent/macromolecular crystal
Each carbon atom covalently bonded to three others forming hexagons [trigonal planar - bond angle 120o]
Layers
4th p electron delocalised – holds layers together; free to move – graphite conducts electricity
Soft
High mp

6. iodine Molecular crystal Strong covalent bonds within molecules
Weak van der Waals forces between molecules

7. ice Molecular crystal Strong covalent bonds within molecules
Strong hydrogen bonds between molecules