What is the difference between valence and conduction bands in metallic bonding?

[Chemist20]

hello,
i have a question related to metallic bonding.

As far as i know, valence band is defined as the highest filled level in the band and conductionband as the 1st unfilled level. So, if I have 100 Li, we will have 100 orbitals which form a band. Since we have 100electrones, 50 pairs, so we occupy half of the band right? then... valence band would be level 50 and conduction band 51? or is it more like: the all the filled leves form de valence band and all the empty ones the conduction band?Also, for a transition metal for example, what would the valence bond be for eg Cr? i mean, how do you define valence band? does it always have to be full?

 

[Wolfgang2b]

You have to look not only at the available states as bands but also at the distribution probability (Fermi-Dirac for electrons)

The position of Fermi energy determines to which level electrons are filled at 0 K. The Fermi energy can be in the valence band/conduction band and the states till that level is filled.

It so happens that for metals, at the Fermi energy, both the conduction and valence bands overlap. Basically there is no energy higher than the thermal energy required for electrons to move in the conduction band.

You might check this page
http://hyperphysics.phy-astr.gsu.edu/hbase/solids/band.html