CHAPTER 1 Stereochemistry and Bonding in Main Group Compounds: 23 Limitations of VSEPR Theory The VSEPR theory is pretty much successful in explaining a wide range of geometries in main group chemistry but there are some serious limitations also for which it offers no rational solution. Some of the most common limitations of the VSEPR theory are given below. 1. The valence-shell-electron-pair-repulsion theory has no sound explanation for molecular geometries having very polar bonds; like Li 2 O is linear whereas its counterpart H 2 O is bent is nature. 2. The VSEPR theory offers no solution for molecular geometries with a high magnitude of π-cloud delocalization. 3.
It does not consider the “inert pair effect”, and thus fails to rationalize the bonding characteristic in molecular geometries possessing the same. For example, [SeCl 6 ] , [TeCl 6 ] and [BrF 6 ] are expected to adopt a pentagonal bipyramidal structure due to seven electron pair domains but are found to be octahedral systems. 4. It fails to predict the structure of transition metal complexes. For example, many bivalent complexes of nickel are square-planar and not tetrahedral. 5. The VSEPR theory does not consider the wave function treatment of chemical bonds and therefore fails to explain many bond length and bond angle variations.
For example, the bond C−Cl bond length decreases as we move from CH 3 Cl to CCl 4 , which is unexpected because of the larger size of Cl in comparison to H. Copyright © Mandeep Dalal