Delocalized Electrons

Also known as Bloch electrons.

These are formed when atoms combine together, and hence the electron shells come closer together but remain in two different states - of being closer or farther.

Thus a close valence band and a far away conduction band are formed.

The electrons in the conduction band are called delocalized electrons, and these can move about from one atom to another when free, and therefore provide the ability to conduct current.