The electron configuration of a Silicon atom in its ground state is $\ce{1s^2 2s^2 2p^2 3s^2 3p^2}$, or equivalently, $\ce{[Ne] 3s^2 3p^2}$.

When looking at the energy-level scheme of a silicon atom, the valence electrons are distributed over two separate energy levels; specifically, the $\ce{3s}$ and $\ce{3p}$ energy levels. It is then said that, as you bring multiple Silicon atoms closer together, the two energy levels will split and overlap. And because the two energy levels are splitting and overlapping, they will produce two energy bands separated by a region of energy that is not allowed. Of these two energy bands, the lower energy band is referred to as the valence band, and the higher energy band is referred to as the conduction band.

I am familiar with the phenomena of valence and conduction bands, as well as the "region of energy that is not allowed", otherwise commonly referred to as the "forbidden energy gap".

However, I'm wondering what this phenomenon of the valence electrons being distributed over two separate energy levels is? How does one reconcile this with the electron configuration $\ce{1s^2 2s^2 2p^2 3s^2 3p^2}$, which seems to suggest that the electrons remain in discrete, well-defined energy levels (rather than overlapping)?

I would appreciate it if people would please take the time to clarify this.

  • $\begingroup$ I have been asking leading spectroscopists as to how they came up the assigning electron configurations of elements. Most chemists are clueless yet we are happy to teach and regurgitate electronic configurations. Better ask in a physics forum where you might get an idea as to who came up with the concept of conduction band and valence bands and why. This was all done by physicists. $\endgroup$
    – AChem
    Jan 17, 2020 at 4:23
  • $\begingroup$ @M.Farooq Oh really? So it would be better to ask physics.stackexchange? $\endgroup$ Jan 17, 2020 at 4:24
  • $\begingroup$ Yes, and even better find the original papers (you can add a request in the question). By going through the original papers you will get a feeling of their line of thinking and reasoning. $\endgroup$
    – AChem
    Jan 17, 2020 at 4:27
  • $\begingroup$ Honestly I might agree with the comments above but I don't understand the question. $\endgroup$
    – Alchimista
    Jan 17, 2020 at 8:55
  • 1
    $\begingroup$ chemistry.stackexchange.com/questions/22354/… might be what you are looking for. Plus does this pic, eg, helps? - - > wiki.chemprime.chemeddl.org/articles/m/o/l/… $\endgroup$
    – Alchimista
    Jan 17, 2020 at 9:36