Why Is Atom Stable When Valence Shell Is Filled With 8 Electrons?

[Dual Op Amp]

I have looked every where, my encyclopia set, the search engine even a different post on this forum, but I just can't find out why an atom is more stable, when the valence shell is filled with eight electrons.

 

[Mike H]

Dr. Transport answered this question in the Atoms, Molecules, and Solids forum - filling a valence shell is energetically favorable as seen by the physics of atoms and molecules. Its chemical inertness is a consequence of the filled valence shell - to either remove or attach an electron is far too costly in terms of the energetics.

The 8 electron rule is only valid for atoms and molecules in the early part of the periodic table (excluding, of course, hydrogen and helium). If you should in the course of your life study inorganic and organometallic chemistry, you will find mention of an "18-electron rule," which states that 18 valence electrons is the desired end result. This is because the d-orbitals become far more important in the chemistry of such atoms and compounds.

 

[gravenewworld]

As my P chem professor always used to say, science doesn't answer the question why but how.

 

[movies]

My Dad asked me this very question once and the only answer I could give him is that's just the way it is. I think that this is just an empirical observation, there isn't a particular reason. Isn't that also the case with the quantum mechanical explanation? Quantum mechanics is made to model the observed behavior of molecules.

If someone thinks I am wrong here and there is a solid quantum explanation for this, I would love to know too!