For small numbers of atoms, you can draw the possible overlaps to understand the patterns of energy levels, as done with allyls in a previous post. But the important result of band theory is that the molecular orbitals are approximated as blending into a continuous line.
The band has finite end points. Electrons are considered free to move inside the band. This stuff is why metals are described in A-level as "a sea of freely moving electrons". The above example is a s-band, but this merging can also be done with p orbitals to make a p-band:
Since p orbitals are higher in energy than s, p-bands are higher in energy than s-bands. These bands can overlap, or they can have a band-gap between them:
You can likewise create d-bands. In fact, orbital overlap in band theory (and MO in general) does not have to happen between orbitals with the same letters. For example, the d orbitals of a metal might overlap with the p orbitals of oxygen.
Elements in the first period do this at room temperature with their s electron. Why does hydrogen form H2 instead? What makes the 1s orbital so special? The s orbital is spherical so it can't be directionality.
ReplyDeleteThe 1s orbital also lacks electron shielding, is very unpolarizable, and doesn't have a p band to overlap with.
DeleteI don't yet know how they translate into explaining why hydrogen isn't a metal.