MolecularGeometry - Molecular Geometry and Chemical Bonding...

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Unformatted text preview: Molecular Geometry and Chemical Bonding Chapter 10 Introduction Each molecule in the nature has a definite shape. BF 3 and NF 3 have the same general formula AX 3 , where A is the central atom to which surrounding atoms, X, are bonded. BF 3 is the planar molecule with a bond angle 120 where as NF 3 is a nonplanar molecule with a bond angle of 96 . The geometry of BF 3 is trigonal planar and that of NF 3 is trigonal pyramidal. There is no relation between the formula of a compound and the shape of its molecules. How do we explain the geometries of the molecules in terms of their electronic structures? Topics of Discussion The Valence-Shell Electron Repulsion(VSEPR) Theory Dipole Moment and Molecular Geometry Valence Bond Theory Description of Multiple Bonding Principles of Molecular Orbital Theory Electron Configurations of Diatomic Molecules of the Second Row Elements Molecular Orbitals and Delocalized Bonding Molecular Geometry and Directional Bonding Molecular geometry of a molecule is the arrange_ ments of atoms in space. Electron-pair geometry is the arrangements of electron pairs around the central atom. Structural formula(lewis electron-dot) indicates which atoms are bonded to each other with bonding e-pairs and where the non-bonding e- pairs are located in molecule. The Valence-Shell Electron Repulsion(VSEPR) Model The electrons are in pairs in the valence shell of atoms in a molecule. The bonding e-pair forms a covalent bond but nonbonding(lone) e-pair doesnt. VSEPR Model states that valence-shell e- pairs are arranged about each atom so that e- pairs stay as far away from another as possible, thus minimizing e-pair repulsions. The direction in space of the bonding pairs gives the geometry of the molecule. In VSEPR model, each multiple bond is treated as though it were a single bonding e- pair(except a slight distortion on bond angles) Prediction of Geometry by VSEPR : F Be F : .. .. .. ..-- pairs- e bonding 2 .. .. .. .. O C O = = pairs- e bonding ) 2(! L in ear Linear Linear L inear Two Electron Pairs 1. Write down the Lewis electron dot formula 2. Determine the number of e-pairs around the CA 3. Arrange the geometry of e-pairs around the CA 4. Decide the molecular geometry from direction of bonding e-pairs Steps to be followed to predict the geometry of an AX n molecule by VSEPR model. A is the central atom (CA) in the molecule....
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MolecularGeometry - Molecular Geometry and Chemical Bonding...

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