Metallic bonding

There are strong forces of attraction within a metal and this is attributed to metallic bonding.

Metals have a sea of delocalized electrons within its structure. These electrons have become detached and the remaining atoms have a positive charge. This positive charged is attracted to the delocalized sea of electrons due to electrostatic forces of attraction (forces which result from unlike charges), and as a result has a strong interaction. It is this interaction which makes the metals so hard and rigid.
The diagram below shows the metallic bonding.