Metals usually have the following properties:

High melting temperature
Good electrical conductivity
Good thermal conductivity
Malleability
Ductility
Between one and three electrons in their outer shells
Low ionisation energies
Increasing electrical conductivity with increasing number of outer electrons

These properties are largely due to the presence of delocalised electrons - electrons that are free to move throughout the structure without being localised between any pair of cations.

There is an electrostatic force of attraction between the nuclei of the cations and the delocalised electrons which is known as metallic bonding.

Metallic Bonding