NSCI 1322 Lecture Notes - Lecture 18: Crystal Field Theory, Ligand Field Theory, Valence Bond Theory
12 Jan 2017
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Document Summary
A complex is formed when electron pairs from ligands are donated to a metal ion. This does not explain how the metal ion can accept electron pairs. Nor does it explain the paramagnetism often observed in complexes. Valence bond theory provided the first detailed explanation of the electronic structure of complexes. According to this view, a covalent bond is formed by the overlap of two orbitals, one from each bonding atom. In the usual covalent bond formation, each orbital originally holds one electron, and after the orbitals overlap, a bond is formed that holds two electrons. In the formation of a coordinate covalent bond in a complex, however, a ligand orbital containing two electrons overlaps an unoccupied orbital on the metal atom. Although valence bond theory explains the bonding and magnetic properties of complexes, it is limited in two important ways: first, the theory cannot easily explain the color of complexes, second, the theory is difficult to extend quantitatively.
