The holistic molecule

Abstract

The quantum and classical views of a molecule are worlds apart, and only the latter has gained popularity in the chemical community. The classical model considers a molecule as a set of atoms connected through electron-pair bonds, structured according to simple valence rules. What is widely considered to be a quantum-mechanical molecular model is defined by electron-pair bonds directed by hybrid orbitals. By showing that orbital hybridization amounts to a simple rotation of coordinate axes and that a linear combination of hybrid orbitals violates the exclusion principle, all LCAO models are shown to reduce to the classical. The familiar classical concepts that feature in theories of chemical bonding have no operational meaning in quantum theory. Grafting these variables on a quantum-mechanical description of a molecule amounts to an abstraction that irreversibly breaks the holistic symmetry and conceals the molecule's quantum properties. A molecule is defined quantum-mechanically with a molecular wave function, a quantum potential and quantum torque. The observables associated with these functions are electron density (the unit operator), total energy, electronegativity and orbital angular momentum. No other derived concepts are needed to characterize a molecule or rationalize its chemical and physical properties. The universally valid holistic nature of quantum theory has the important implication that non-local interactions, mediated by the quantum potential, pervade the entire fabric of a molecule. Once this property is recognized, the mysterious attributes of molecules disappear. In principle, quantum potential plays a significant role elucidating chemical reactions, intramolecular rearrangements, crystal growth, polymorphism, polytypism, quasi-crystallinity, enzyme catalysis, allosteric effects, protein folding and the magic of DNA. © 2008 Springer.