After studying chemical bonding I am stuck at a question that is fundamental to my understanding of chemistry:

What is it that makes 8 electrons in the valence shell stable?

I googled it and got answers like it is a "noble gas electron configuration". But that doesn't answer my question. What is so special in the configuration of noble gases that makes them so stable? How does octet give stability to an atom?

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    $\begingroup$ A simple answer would be that there are no empty, low-energy orbitals (it is good to fill those), and also no filled, high-energy orbitals (it is bad to fill those). In truth the octet rule has its limitations. It is only an empirical observation and is not always true. $\endgroup$ – orthocresol Sep 12 '16 at 7:46
  • $\begingroup$ @orthocresol how do you classify a low-energy orbital and a high-energy orbital. Isnt it a comparitive term (what I can infer from ur comment is that s and p are called low-energy while d and f are called high-energy. Am I right?) $\endgroup$ – oshhh Sep 12 '16 at 7:56
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    $\begingroup$ No. The energy increases in the order 1s, 2s, 2p, 3s... for the purposes of this discussion, we talk about Ne. Here we might consider 1s, 2s, 2p "low" and 3s "high" because it is in a higher shell. Therefore it is advantageous to fill 1s, 2s, 2p, but not to fill 3s. The same logic applies when discussing why fluorine forms $\ce{F-}$ and not $\ce{F^2-}$. The rationalisation of the octet rule is therefore just a generalisation of that to covalent compounds. $\endgroup$ – orthocresol Sep 12 '16 at 7:58