On Chemical Bonding

Let us cite from the Preface of The Chemical Bond Fundamental Aspects of Chemical Bonding (eds Frenking an Shaik) 2014) :

• One of the fundamental territories of chemistry is the chemical bond, the glue from which an entire chemical universe is constructed. 
• The bond is becoming again a central intellectual arena. This ‘‘return of the bond’’ has prompted the two editors to edit these two volumes on bonding, and it is only fitting that their publication date is close to the centenary of the Lewis seminal paper on electron-pair bonding.
• The first revolution is the ‘‘compositional revolution’’ that started with Lavoisier and culminated in the atomic hypothesis of Dalton.
• Starting in the late 1920s, the new quantum theory has entered chemistry and ushered the third revolution through the works of Heitler and London and subsequently by Pauling, Slater, Mulliken and Hund, Huckel, and so on. 
• Here, we have to digress for a moment and remark about the current tendency to classify chemistry as a service science and a sub-branch of physics.
• Covalent bonding involves a synergism between several interactions with quite different physical attributes and quantitative characteristics. 
• On the one hand, the lowering of the energy that establishes the bond is the result of a variational competition between the kinetic energy and potential energy. 
• On the other hand, there occurs an intricate interplay between various intra-atomic and interatomic interactions. 
• These basic agents have, moreover, to accommodate electron correlation. 
• It emerges that, in all cases, the driving force of covalent bond formation is the lowering of the kinetic energy gained by the delocalization of electronic waves over more than one atom. 
• This observation is only superficially discordant with the virial theorem which, as mentioned earlier, requires the molecule to have a higher total kinetic energy than the separated atoms. 
• The in-depth accounting of all interconnections between the various interactions shows that the information disclosed by the actual total kinetic and potential energies per se is insufficient for drawing any inferences regarding the origin of covalent bonding.

We learn from this exposition that the mystery of covalent chemical bonding has not been clarified by the new quantum theory and so awaits an explanation on physical grounds. This is were RealQM appears to open a window to new understanding.