The notorious sceptic


The comment "Nothing else is necessary" *) may be challenged. If we look at the electronic ground state of a molecule then this may really be all. That is the domain of Kimball's model. Some contributions on this site do probe deeper. And then: Nothing is so simple, anymore: Excite a molecule with photons as in photoelectron and electronic spectroscopy. Then you observe resonant processes revealing energy levels of CH4 as shown here. It turns out that the electrons of the four equivalent C-H bonds show two different resonances which we model by an occupation of two different energy levels with occupation 2 + 3*2, not 4*2 in one level!

Even the simple water molecule of highschool and tutorial6 appears to be more complex: the two lone pairs at O again show two resonances, hence are not equivalent. One is of σ-type and in the HOH plane, the other of π-type and perpendicular to that plane!

But this complex situation in CH4 and H2O does not manifest itself if you observe chemical reactions of these molecules not far away from the ground state.

Another case is the double bonded O in the carbonyl group >C=O>. This is shown as Kimball result for formamide. You may turn the 3D pictures around with the mouse if you have downloaded the free Wolfram-CDF player.
All these statements are experimentally proven and are predicted by good quantum chemistry. I may also mention the complex case of the O2 molecule, which is paramagnetic and has two unpaired electrons, nothing like <O=O> of highschool or the naive Lewis model. And this is observable macroscopically with the ground state molecule: Pour liquid oxygen into the polegap of a permanent magnet. The liquid is attracted magnetically and sticks to the poles contrary to liquid nitrogen which flows through the gap unimpeded and is diamagnetic.

Maybe, I'll make another tutorial to show that this "strange" behavior can be modelled by Kimball's idea. It has something to do with electrons not liking to pair up if there is a lower energy state available with two single electrons (in Switzerland wedded pairs pay higher taxes than unwed ones, certainly a valid analogy!).

However, let's not get too agitated: Our description of the electronic structure of molecules should be commensurate to what we want to explain or understand. For many observations of e.g. methane and its chemistry we do not need to know the reactions of its electron distribution to an exciting electromagnetic field.

*) You may have noticed in tutorials 5,6 that the electronic ground state of CH4 and its tetrahedral shape is completely derivable from electrostatics and Pauli's principle, applied to C+6 and 4 H+ nuclei and 10 electrons with zeropoint energy! Nothing else is necessary.