lecture 7 - Review of VB and MO theory Lecture 7, Chemistry...

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Review of VB and MO theory Lecture 7, Chemistry 312
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Brief history of VB theory After Gilbert Newton Lewis published “The Atom and the Molecule” in 1916, in which he introduced the idea of a covalent bond, chemists wanted to gain a better and more mathematical description of what the chemical bond actually was. In 1926, Erwin Schrodinger published the quantum mechanical interpretation of energy levels in an atom (Schrodinger’s equation), and the next year, Walter Heitler and Fritz London use it to come up with a mathematical model for the H 2 molecule – this is the forerunner of valence bond theory.
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VB theory Linus Pauling combined Lewis’s ideas of covalent bondng (shared electron pairs) with the Heitler-London calculation to expand VB theory to a larger group of molecules, published in a 1927 paper “The Shared-Electron Chemical Bond”. He added the ideas of resonance and orbital hybridization later, and in 1936, published The Nature of the Chemical Bond . Because of his insistence on the supremacy of the analysis of VB theory, Pauling did not embrace molecular orbital theory.
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Formation of σ and π (covalent) bonds
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The road to MO theory Molecular orbital theory began nearly at the same time as VB theory. Friedrich Hund and Robert Mulliken (electron delocalization over a whole molecule), John C Slater (linear combination of atomic orbitals), John Lennard-Jones (potential between two noble gas atoms), all published papers on these topics in 1927- 1928. Mulliken coined the word “orbital” in 1932,
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lecture 7 - Review of VB and MO theory Lecture 7, Chemistry...

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