The bulk properties of a material, such as melting point, hardness and conductivity, come from the bonds in it and how its particles are arranged. A single atom of copper does not conduct electricity or melt like a piece of copper wire. These properties belong to the many atoms or ions bonded together.
- Ionic compounds: a giant lattice of oppositely charged ions held by strong electrostatic forces in all directions. They have high melting points. They conduct electricity when molten or dissolved because the ions are free to move, but not when solid. They are brittle.
- Simple molecules: strong covalent bonds inside the molecules but weak intermolecular forces between them. They have low melting and boiling points and do not conduct, because they have no free electrons or ions.
- Giant covalent structures: strong covalent bonds throughout, as in diamond, so they have very high melting points and are hard.
Polymers are long chains of atoms joined by covalent bonds. The intermolecular forces between long chains are stronger than those between small molecules, so polymers are solid at room temperature. Metals are giant structures of positive ions in a sea of delocalised electrons. The strong metallic bonding gives high melting points, and the moving electrons let metals conduct. The layers of ions can slide over each other, so metals can be bent and shaped.