Explain how the structure of metals allow them to form metallic bonds.

A giant metallic lattice – the crystal lattice of metals consists of regularly arranged  ions (NOT atoms) surrounded by a ' delocalised sea of electrons' that form the giant lattice. 

The outer electrons (–) from the original metal atoms are free to move around between the positive metal ions formed (+).

These 'delocalised' electrons from the outer shell of the metal atoms are the 'electronic glue' holding the particles together.

There is a strong electrostatic force of attraction between the 'sea' of delocalised electrons) (–) and the 'immobile' positive metal ions (+) that form the giant lattice and this is the metallic bond. The attractive force acts in all directions.

Metallic bonding is not directional like covalent bonding, it is like ionic bonding in the sense that the force of attraction between the positive metal ions and the mobile electrons acts in every direction about the fixed (immobile) metal ions of the metal crystal lattice, but in ionic lattices none of the ions are mobile.

This a big difference between a metallic bond and an ionic bond.