2.7.1 Metallic bonding and the properties of metals

Metallic bonding

1. In a solid metal, the atoms are packed closely together in a regular arrangement called a giant metallic lattice.
2. Each metal atom loses its outer-shell electrons, which turns the atoms into positive ions.
3. The electrons that have been lost do not belong to any one ion, so they become delocalised and move freely throughout the whole lattice.
4. These delocalised electrons form a sea of electrons that surrounds the positive ions.
5. Metallic bonding is the electrostatic attraction between the positive ions and the sea of delocalised electrons.
6. The attraction acts in all directions, so each positive ion is held in the lattice by the electrons all around it.
7. In magnesium, each atom gives up its two outer-shell electrons, so the lattice is made of ${Mg}^{2+}$ ions surrounded by a sea of delocalised electrons.

Electrical conductivity of metals

1. Metals are good conductors of electricity, because they contain delocalised electrons that are free to move through the lattice.
2. When a voltage is applied across a piece of metal, the delocalised electrons drift through the lattice towards the positive terminal.
3. This flow of charged electrons through the metal is an electric current.
4. The delocalised electrons are present whether the metal is solid or liquid, so metals conduct in both states.
5. The positive ions stay in their places in the lattice and do not carry the current.

Malleability and ductility

1. The positive ions in a metal lattice are arranged in layers.
2. When a force is applied to a metal, the layers of positive ions can slide over one another into new positions.
3. The delocalised electrons move with the ions, so the metallic bonding is not broken and still holds the ions together in their new positions.
4. Metals can therefore change shape without breaking.
   1. Metals are malleable, so they can be hammered or rolled into thin sheets, such as aluminium foil.
   2. Metals are ductile, so they can be drawn out into thin wires, such as copper wire.
5. An ionic lattice behaves differently, because sliding a layer brings ions with the same charge next to each other, so they repel and the crystal shatters.