What's a good primer of band theory (metals and semiconductors).

[aleksbooker]

Edit: I've made some progress on this one, and I now understand that the valence and conductance bands are composed of molecular orbitals contributed by each metallic atom joining the molecule.

For example, three lithium atoms would contribute three total molecular orbitals, resulting in three bands. The bottom two might be the valence bands and hold all the elections, while the third might be the conductance band.

Here's the question:

Why does that third band (the conductance band) have a higher energy level than the valence bands, especially if they were all the same type of orbital (2s) contributed by lithium atoms?

 

[DrClaude]

Edit: I've made some progress on this one, and I now understand that the valence and conductance bands are composed of molecular orbitals contributed by each metallic atom joining the molecule.

For example, three lithium atoms would contribute three total molecular orbitals, resulting in three bands. The bottom two might be the valence bands and hold all the elections, while the third might be the conductance band.

Here's the question:

Why does that third band (the conductance band) have a higher energy level than the valence bands, especially if they were all the same type of orbital (2s) contributed by lithium atoms?

All orbitals of the same type will contribute the the same band. In the case of lithium, the 2s orbitals will make up the s-band. Since each lithium atom contributes only one electron to the s-band, it is half-filled and electrons can move from one atom to the next, so it is a conduction band.

If the s-band was completely filled, then it would become a valence band, and the higher energy p orbitals would form the p-band, which would be the conduction band, and there would be a band gap between the two, due to the difference in energy between s and p orbitals.

 

[aleksbooker]

Oh. That's a great explanation. Why didn't they put *that* in the textbooks?