Chemical Bond

Credit for the development of the modern theory of chemical bonding belongs largely to the great American chemist Linus Pauling. Early in his career, Pauling learned about the revolution in physics that was taking place largely in Europe during the 1920s. That revolution had come about with the discovery of the relativity theory, quantum mechanics, the uncertainty principle, the duality of matter and energy, and other new and strikingly different concepts in physics.

Most physicists recognized the need to reformulate the fundamental principles of physics because of these discoveries. Relatively few chemists, however, saw the relevance of the revolution in physics for their own subject. Pauling was the major exception. By the late 1920s, he had already begun to ask how the new science of quantum mechanics could be used to understand the nature of the chemical bond.

In effect, the task Pauling undertook was to determine the way in which any two atoms might react with each other in such a way as to put them in the lowest possible energy state. Among the many discoveries he made was that, for most cases, atoms form neither a purely ionic nor purely covalent bond. That is, atoms typically do not completely lose, gain, or share equally the electrons that form the bond between them. Instead, the atoms tend to form hybrid bonds in which a pair of shared electrons spend more time with one atom and less time with the second atom.