3.3 Metallic bonding

Metal atoms are arranged in a regular, tightly packed lattice. When the atoms pack together, their outer-shell electrons become delocalised, so they are no longer associated with one particular atom.

The metallic structure is therefore a lattice of positive metal ions surrounded by a mobile sea of delocalised electrons. The positive ions remain in the lattice while the delocalised electrons move through the structure.

Metallic bonding is the strong electrostatic attraction between the positive metal ions and the surrounding delocalised electrons. This attraction holds the ions in place, counteracts repulsion between positive ions and maintains the stability of the metal structure.

Do not describe metallic bonding as attraction between neutral atoms or as one covalent electron pair shared by two atoms. The delocalised-electron model defines the bond here; detailed explanations of conductivity, malleability, alloys or property trends belong to later supported objectives.