Valence Bond Theory - Philosophical Concept | Alexandria
Valence Bond Theory: A quantum mechanical theory that explains chemical bonding as the overlap of atomic orbitals, leading to the formation of a covalent bond. This seemingly straightforward explanation masks a complex history and a continuing evolution of understanding, challenging preconceived notions about how atoms truly interact. Early seeds of Valence Bond (VB) Theory can be traced to Gilbert N. Lewis’s 1916 publication, “The Atom and the Molecule,” laying the groundwork for understanding electron pair bonds. However, the theory formally took shape in the late 1920s, spearheaded by Walter Heitler and Fritz London's quantum mechanical treatment of the hydrogen molecule in 1927. Their work, appearing in Zeitschrift fur Physik, marked a profound shift in understanding chemical bonding, moving beyond classical electrostatics. Linus Pauling further popularized and expanded the theory in his seminal 1931 paper "The Nature of the Chemical Bond," published in the Journal of the American Chemical Society.
Over the decades, VB theory has undergone periods of both prominence and relative decline. While conceptually intuitive and adept at describing localized bonding, it faced computational challenges in handling larger, more complex molecules compared to Molecular Orbital Theory. The rise of computational chemistry in the latter half of the 20th century initially favored Molecular Orbital approaches due to their easier implementation. However, in recent years, there has been a resurgence of interest in VB theory, driven by advances in computational methods and a renewed appreciation for its ability to provide chemically insightful descriptions of bonding, particularly in systems with strong electron correlation. The persistent allure of VB theory lies in its grounding in readily visualizable concepts – atomic orbitals, overlap, and resonance – offering a compelling, if sometimes simplified, narrative of the chemical bond. The modern interpretations continue to evolve, raising questions about the limits of localization and the true nature of electron behavior in the making and breaking of chemical bonds.