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1 subject chemistry paper no and title paper 3 stereochemistry metal ligand equilibria and reaction mechanism of transition metal complexes module no and title module 1 valence shell electron pair ...

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                  Subject                 Chemistry 
                  Paper No and Title      Paper  3:  (Stereochemistry,  Metal-Ligand  Equilibria  and 
                                          Reaction Mechanism of Transition Metal Complexes) 
                  Module No and Title     Module 1: Valence-Shell Electron-Pair Repulsion (VSEPR) 
                                          Theory 
                  Module Tag               CHE_P3_M1 
                  
                  
                                                                                                   
                  
      CHEMISTRY                    Paper 3: (Stereochemistry, Metal-Ligand Equilibria and 
                                   Reaction Mechanism of Transition Metal Complexes) 
                                   Module 1: Valence-Shell Electron-Pair Repulsion (VSEPR) 
                                   Theory 
                  
                  2 
      
                   
                  TABLE OF CONTENTS                  
                   
                     1.  Learning Outcomes 
                     2.  Introduction 
                     3.  Basic Assumptions of VSEPR Theory 
                     4. The Valence Shell Electron-pair Repulsion (VSEPR) Model 
                     5. Predicting Molecular Geometries    
                     6.  Four or Fewer Valence-Shell Electron Pairs 
                     7.  The Effect of Nonbonding Electrons and Multiple Bonds on Bonds    Angles  
                     8.  Molecules with no central atom 
                     9.  Summary 
                      
                      
                      
                   
                      
                                                     
                   
       CHEMISTRY                    Paper 3: (Stereochemistry, Metal-Ligand Equilibria and 
                                    Reaction Mechanism of Transition Metal Complexes) 
                                    Module 1: Valence-Shell Electron-Pair Repulsion (VSEPR) 
                                    Theory 
                   
                     3 
       
                              
                     1. Learning Outcomes 
                      
                     After studying this module, you shall 
                         •   Learn the basic assumptions of VSEPR theory  
                         •   Understand the VSEPR Model 
                         •   Be able to predict molecular geometries that deal with Lewis structures containing 
                             bonding & nonbonding pairs of electrons 
                         •   Analyze the effect of Nonbonding Electrons and Multiple Bonds on Bond Angles 
                         •   Know the application of VSEPR model for predicting the geometrical shapes of 
                             molecules through their Lewis structures.  
                         •   Explore  the  application  of  VSEPR  Model  for  determining  the  structure  of 
                             molecules with no-central atom. 
                     2. Introduction                                                                                                     
                      
                     Molecules of different substances have diverse shapes. Atoms attach to each other in 
                     various geometric arrangements. The overall molecular shape is determined by its bond 
                     angles in space. The shapes of the molecules can be predicted from their Lewis structures 
                     as  prescribed  in  the  model  presented  in  the  Valence-Shell  Electron-Pair  Repulsion 
                     (VSEPR) theory. The base of VSEPR theory was laid down by N.V. Sidgwick and H.M. 
                     Powell in the 1930’s but modern formulation of VSEPR theory was proposed by R. 
                     Nyholm and R.J. Gillespie. VSEPR theory is used for predicting the shapes of individual 
                     molecules based on the extent of interactions of electron pairs in the valence shell of the 
                     atoms. It explains the shape of the molecules having localized electron pairs, bonded or 
                     nonbonded. The shape of a molecule is very important for studying its physical and 
                     chemical properties. 
                      
                     The VESPs are regarded as occupying the localized orbitals with proper orientations in 
                     space so as to minimize the coulombic repulsion between the electron pairs leading to 
                     stable spatial arrangement. The stable spatial arrangements of 2,3,4,5 and 6 electron pairs 
                     with minimum inter-electron repulsion are linear, trigonal planar, tetrahedral, trigonal 
                     bipyramidal and octahedral respectively. 
                         3.  Basic Assumptions of the VSEPR Theory  
                                                                                                      
                     The  bond  angles  in  a  species  depends  upon  (i)  interatomic  van  der  waal  repulsion 
                     amongst the nonbonded atoms, (ii) coulombic repulsion due to partial charges on the 
                     atoms due to electronegativity differences, or (iii) repulsion between the electron pairs on 
                      
        CHEMISTRY                          Paper 3: (Stereochemistry, Metal-Ligand Equilibria and 
                                           Reaction Mechanism of Transition Metal Complexes) 
                                           Module 1: Valence-Shell Electron-Pair Repulsion (VSEPR) 
                                           Theory 
                      
                     4 
       
                     the bonded atoms. Of all the three terms, (iii) i.e. repulsion between the electron pairs on 
                     the bonded atoms, is the most important affecting the geometry of the species.  There are 
                     three types of repulsion that take place between the electron pairs of a molecule: 
                      
                         •   The lone pair-lone pair repulsion 
                         •    The lone pair-bonding pair repulsion 
                         •    The bonding pair-bonding pair repulsion. 
                      
                     The repulsion between the lone pair (LP) electrons are greater than those between the 
                     bonded pairs (BP). For a stable molecule these repulsions must be minimised. When 
                     repulsion cannot be avoided, the weaker repulsion (i.e. the one that causes the smallest 
                     deviation from the ideal shape) is preferred. The order of the repulsion between various 
                     types of LP is given as: 
                      
                     LP-LP>LP-BP>BP-BP 
                      
                     This is due to the absence of second nucleus at the distal end of the LP. The nucleus at 
                     the either ends of the electron pair tends to polarize the electron cloud in the internuclear 
                     regions. The LP is attracted only its own nucleus tends to occupy larger angular volume 
                     then  BP.  Further,  double  bonds  occupy  more  angular  space  than  single  bonds.  Also 
                     bonding to more electronegative substituent occupies less space than bonding to a less 
                     electronegative substituent. If the central atom belongs to a third or higher period, the 
                     above rules apply for bonding to halogens and oxygen atoms only. For other atoms, the 
                     LP occupies nonbonding s orbitals and bonding is through p orbitals, e.g. in phosphine 
                     (bond angle 94̊) or in arsine (bond angle 92̊). 
                     The valence bond theory and VSEPR theory is usually compared with each other. The 
                     valence bond theory deals with the molecular shape through orbitals that are energetically 
                     accessible for bonding and mainly concerns with the formation of sigma and pi bonds. 
                     Another  model  named  molecular  orbital  theory  also  describes  that  how  atoms  and 
                     electrons are assembled into molecules and polyatomic ions.  
                     VSEPR theory was structurally accurate and molecular geometries of covalent molecules 
                     have  been  predicted  successfully.  VSEPR  theory  has  been  criticized  for  not  being 
                     quantitative.  The  shape  of  a  molecule  can  be  related  to  following      five  basic 
                     arrangements. 
                      
                      
                      
                      
        CHEMISTRY                          Paper 3: (Stereochemistry, Metal-Ligand Equilibria and 
                                           Reaction Mechanism of Transition Metal Complexes) 
                                           Module 1: Valence-Shell Electron-Pair Repulsion (VSEPR) 
                                           Theory 
                      
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...Subject chemistry paper no and title stereochemistry metal ligand equilibria reaction mechanism of transition complexes module valence shell electron pair repulsion vsepr theory tag che p m table contents learning outcomes introduction basic assumptions the model predicting molecular geometries four or fewer pairs effect nonbonding electrons multiple bonds on angles molecules with central atom summary after studying this you shall learn understand be able to predict that deal lewis structures containing bonding analyze bond know application for geometrical shapes through their explore determining structure different substances have diverse atoms attach each other in various geometric arrangements overall shape is determined by its space can predicted from as prescribed presented base was laid down n v sidgwick h powell s but modern formulation proposed r nyholm j gillespie used individual based extent interactions it explains having localized bonded nonbonded a molecule very important ...

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