GRADE XII CHEMISTRY READ AND GET THE CLEAR CONCEPT ABOUT: Valence Shell Electron Pair Repulsion Theory This is a theory to predict the shapes of molecules. It was given by Sidwick and Powel in 1940. VSEPR theory stands for Valence Shell Electron Pair Repulsion theory. This theory is based on the idea that electron pairs try to be as far apart as possible to minimize the repulsion. The main assumptions of VSEPR theory are as follows: 1. In a simple co-valent compound, there is a central atom to which all other atoms are attached. 2. The valence shell of the central atom contains electrons in pairs which may be bonding pairs or non-bonding (lone) pairs. 3. A lone pair of electron repels more than a bonded pair, so that the order of repulsion is, BP, BP < BP, LP < LP, LP 4. The molecules take the shape that tends to minimize the electrostatic repulsion between electron pairs. 5. Greater is the electro-negativity difference between central atom and the atom attached to it, greater is the magnitude of repulsion. 6. In multiple bonding for molecular geometry consideration, the multiple bonds are to be considered as only one electron pair. Notes: a) Shape of molecule is determined by α-ray (alpha-ray) diffraction and by determining the bond length and bond angles. b) In case of diatomic molecules, there will be only one bond and the molecules have linear geometry. VSEPR theory is an important topic for plus two chemistry in HSEB exam. It is because of the inclusion frequency of questions regarding to various applications (e.g. prediction of geometry) of this theory in Grade 12, Chemistry.
Posted on: Fri, 25 Oct 2013 01:59:18 +0000
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