Does overlapping of valence orbitals take place in metallic bonding?
Yes, it does. It’s a little complex, so the explanation really depends on what level of chemistry you’re studying, but in a nutshell the valence atomic orbitals of a metal (for example the 3s orbital of Na) overlap to form MO’s in much the same way that H 1s orbitals overlap to form the MO’s of H2. Bonding and antibonding combinations, in other words. The difference in a metallic solid is that there are vast numbers of AO’s being combined to form the MO’s, so an equally vast number of bonding and antibonding combinations are possible, with those different MO’s being very close in energy. As a consequence, instead of having discrete (quantized) energy levels as you do in “normal” MOs like those of H2, you generate a continuum of MO energy levels called a band. There will actually be two bands, one of which is more bonding in character, while the other is more antibonding. In a metal, those two bands actually overlap. The lowest energy MO’s fill up with the appropriate number of valence
