Metallic bonding
- Metals have giant structures of atoms arranged in a regular pattern.
- The electrons in the outer shells of the metal atoms are delocalised: they are free to move through the whole structure.
- Metallic bonding is the strong attraction between the positive metal ions and the sea of delocalised electrons.
Properties of metals
- Most metals have high melting and boiling points, because metallic bonds are strong.
- Metals are good conductors of electricity, because the delocalised electrons carry charge through the metal.
- They are good conductors of thermal energy, because energy is transferred by the delocalised electrons.
- The layers of atoms can slide over each other, so metals can be bent and shaped (they are malleable and ductile).
Alloys
- Most pure metals are too soft for many uses, so they are mixed with other metals to make alloys, which are harder.
- In an alloy, atoms of different sizes distort the regular layers, making it harder for them to slide over each other.
- Examples: steel (iron with carbon and other elements), brass (copper and zinc), and gold alloys used in jewellery, where purity is measured in carats (24 carat is pure gold).
Key terms
- Metallic bond
- The strong attraction between positive metal ions and delocalised electrons.
- Delocalised electrons
- Electrons that are free to move through a structure.
- Alloy
- A mixture of a metal with other elements, usually other metals.
- Malleable
- Able to be hammered or bent into shape.
- Ductile
- Able to be drawn out into wires.
- Steel
- An alloy of iron with carbon and other elements.
- Brass
- An alloy of copper and zinc.
- Carat
- A measure of the purity of gold; 24 carat is pure gold.