The difference is that an isolated atom has discrete electron energy states and solid materials have electron band structures.
Explanation:
The difference is that an isolated atom has discrete electron energy states and solid materials have electron band structures.
An atom consists of electrons orbiting around a nucleus. That an isolated atom has discrete electron energy states means that electrons cannot choose any orbit they want because they are restricted to orbits with only certain energies. Electrons can jump from one energy level to another, but they can never have orbits with other energies than the permitted energy levels.
The atomic valence orbitals of the atoms of the solid material that will be forming a metallic bond, combine with each other to give molecular orbitals, with very similar energies to each other. So close are these formed molecular orbitals energetically, which give rise to a band. As many molecular orbitals are obtained as atomic orbitals are combined.
In metals, there are valence bands, which are bands in which valence electrons are found and can be full or half full, depending on the electronic configuration of the metal, and conduction bands, which can be empty or partially empty and facilitate driving because they are energetically accessible. In fact, metals are conductive because the valence and conduction bands overlap, causing electrons to move freely from one to another.
In contrast, in semiconductor materials, the valence and conduction bands do not overlap, but the energy difference between the two is small. Then a small energy contribution will allow them to promote electrons to the conduction band and, therefore, conduct the electric current.
Finally, in the insulators the two bands are so far apart that the conduction band is inaccessible. This is the reason why they are unable to conduct the electric current.
