CHAPTER 1 Stereochemistry and Bonding in Main Group Compounds: VSEPR Theory One of the most important discoveries of the 20 th century was Lewis’s description of the chemical bond as a shared pair of electrons. This remarkably brilliant idea connected some of the most important inventions in chemistry from the 19 th century; like the Mendeleev’s periodic table of elements and the van 't Hoff’s formulation of the tetrahedral carbon. Lewis’s idea also laid down the foundation of some advanced theoretical models for chemical bonding used today. The cubical atoms and the concept of shared electron pairs proposed by Lewis in 1919 can be illustrated as shown below. Figure 1.
The Lewis concept of electron-pair sharing between cubical atoms. The valence-shell-electron-pair-repulsion (VSEPR) theory is actually the successor of Lewis's idea which also says that the covalent bond can be portrayed as a shared electron-pair. Now, although Lewis’s model explained the correlation between valence and bonding in an extremely beautiful manner, it had no theoretical basis at that time. Later in 1924, Wolfgang Pauli rationalized the electron pairing by proposing the Pauli exclusion principle. Now being an extension of the Lewis idea, the VSEPR theory also finds its roots in the Pauli exclusion principle.
The initial formulation of the VSEPR model was actually carried out by two British chemists, Nevil Sidgwick and Herbert Powell, who correlated the number of valence shell electron pairs of the central atom in a molecule to the bonding profile around. Copyright © Mandeep Dalal