The 'sea of electrons' model
In a metal, the atoms are packed closely in a regular lattice. Each atom releases its valence electrons, which are free to move throughout the whole structure — they are said to be delocalised. This leaves behind a lattice of positive metal ions (cations) surrounded by a 'sea' of delocalised electrons.
A metallic bond is the strong electrostatic attraction between the positive metal ions and this sea of mobile electrons. Because the electrons belong to no single atom, the bond acts in all directions.
Key idea / 要点
Metallic bond = positive metal ions + a sea of delocalised electrons, held together by electrostatic attraction. The free electrons explain most metal properties.
Properties explained
- Electrical conductivity — delocalised electrons drift when a voltage is applied, carrying current.
- Thermal conductivity — mobile electrons transfer heat energy quickly.
- Malleable and ductile — layers of ions can slide over one another without breaking the bond, because the electron sea moves with them.
- High melting points — strong attractions need much energy to overcome.
Worked example / 例题
Why can copper be drawn into thin wires? When a force is applied, layers of Cu+ ions slide over each other. The delocalised electrons flow around them and keep the metallic bond intact, so the metal changes shape instead of shattering — it is ductile.
Remember / 记住
- Metallic bonding occurs in metals and alloys.
- Delocalised electrons explain conduction, malleability and ductility.
- Metals stay conductive as both solids and liquids.