Valence Bond Theory
In 1927, valence bond theory was formulated and it argues that a chemical bond forms when two valence electrons, in their respective atomic orbitals, work or function to hold two nuclei together, by virtue of effects of lowering system energies. Building on this theory, the chemist Linus Pauling published in 1931 what some consider one of the most important papers in the history of chemistry: "On the Nature of the Chemical Bond". In this paper, elaborating on the works of Lewis, and the valence bond theory (VB) of Heitler and London, and his own earlier works, Pauling presented six rules for the shared electron bond, the first three of which were already generally known:
- 1. The electron-pair bond forms through the interaction of an unpaired electron on each of two atoms.
- 2. The spins of the electrons have to be opposed.
- 3. Once paired, the two electrons cannot take part in additional bonds.
His last three rules were new:
- 4. The electron-exchange terms for the bond involves only one wave function from each atom.
- 5. The available electrons in the lowest energy level form the strongest bonds.
- 6. Of two orbitals in an atom, the one that can overlap the most with an orbital from another atom will form the strongest bond, and this bond will tend to lie in the direction of the concentrated orbital.
Building on this article, Pauling's 1939 textbook: On the Nature of the Chemical Bond would become what some have called the "Bible" of modern chemistry. This book helped experimental chemists to understand the impact of quantum theory on chemistry. However, the later edition in 1959 failed to adequately address the problems that appeared to be better understood by molecular orbital theory. The impact of valence theory declined during the 1960s and 1970s as molecular orbital theory grew in usefulness as it was implemented in large digital computer programs. Since the 1980s, the more difficult problems of implementing valence bond theory into computer programs have been solved largely, and valence bond theory has seen a resurgence.
Read more about this topic: Chemical Bond
Other articles related to "valence bond theory, valence bond, theory, bond, bonds":
... Modern valence bond theory is the application of valence bond theory, with computer programs that are competitive in accuracy and economy with programs for the Hartree-Fock method ... The early popularity of valence bond methods thus declined ... It is only recently that the programming of valence bond methods has improved ...
... In some respects valence bond theory is superior to molecular orbital theory ... When applied to the simplest two-electron molecule, H2, valence bond theory, even at the simplest Heitler-London approach, gives a much closer approximation to the bond energy, and it ... In contrast simple molecular orbital theory predicts that the hydrogen molecule dissociates into a linear superposition of hydrogen atoms and positive and negative hydrogen ions, a completely unphysical ...
... An important aspect of the VB theory is the condition of maximum overlap which leads to the formation of the strongest possible bonds ... This theory is used to explain the covalent bond formation in many molecules ... For example, in the case of the F2 molecule, the F - F bond is formed by the overlap of pz orbitals of the two F atoms, each containing an unpaired electron ...
... this representation, the octet rule is not broken, the bond orders are 1/2, and there is increased electron density in the fluorine atoms ...
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