Valence bond theory

Valence bond theory describes chemical bonds as overlaps between atomic orbitals and represents molecular structure through resonance among localized bonding arrangements.

Atomic orbital: A quantum-mechanical description of an electron’s spatial state in an atom. Valence bond theory builds bonds from the overlap of these atomic electron states.
Schrödinger equation: The equation governing how quantum-mechanical states evolve or satisfy energy conditions. Valence bond theory approximates molecular states using solutions built from atomic wavefunctions.
Molecular orbital theory: A quantum-chemical model that assigns electrons to orbitals extending over an entire molecule. It contrasts with valence bond theory’s localized bonds by treating molecular orbitals as delocalized.
Hydrogen molecule: A molecule consisting of two hydrogen atoms joined by a covalent bond. Its bond is the simplest example of overlap between two atomic orbitals.
Quantum chemistry: The application of quantum mechanics to the structure, properties, and reactions of molecules. Valence bond theory is one of quantum chemistry’s foundational approaches to molecular structure.
Orbital overlap: The shared spatial region of two orbitals, where electron density can contribute to a bond. The model treats overlap between atomic orbitals as the basis of covalent bonding.
Wavefunction: A mathematical function encoding a quantum system’s state and the probabilities of measurement outcomes. Atomic orbitals and molecular bonding arrangements are represented by wavefunctions.
Lewis structure: A diagram showing valence electrons as bonds and lone pairs around atoms. Lewis structures depict bonding patterns, while valence bond theory gives them a quantum-mechanical basis.
Methane: A molecule with one carbon atom bonded to four hydrogen atoms. Its tetrahedral bonds are commonly described using carbon hybrid orbitals.
Walter Heitler: A German physicist who, with Fritz London, developed an early quantum-mechanical treatment of the hydrogen molecule. His 1927 work helped establish the quantum-mechanical account of chemical bonding.

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