Chpt9 - Chapter 9 Molecular Geometries and Bonding Theories...

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Chapter 9 Molecular Geometries and Bonding Theories
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Molecular Shapes The shape of a molecule plays an important role in its reactivity. Lewis structures do not provide the molecular shape By noting the number of bonding and nonbonding electron pairs we can predict the shape of the molecule.
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Electron Domains We can refer to the electron pairs as electron domains . Nonbonding electrons, single, double or triple bonds all count as one electron domain. Lewis structures can be used to predict the number of electron domains This molecule has four electron domains.
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What Determines the Molecular Structure of a Molecule? Simply put, electron pairs, whether they be bonding or nonbonding, repel each other. By assuming the electron pairs are placed as far as possible from each other, we can predict the shape (structure) of the molecule.
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Valence Shell Electron Pair Repulsion Theory (VSEPR) “The best arrangement of a given number of electron domains is the one that minimizes the repulsions among them.” Only valid for compounds containing representative elements.
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Balloon Geometries
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Electron- Domain Geometries These are the electron-domain geometries for two through six electron domains around a central atom.
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Electron-Domain Geometries All one must do is count the number of electron domains in the Lewis structure. The geometry will be that which corresponds to that number of electron domains.
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Molecular Geometries The electron-domain geometry is often not the shape of the molecule, however. The molecular geometry is that defined by the positions of only the atoms in the molecules, not the nonbonding pairs.
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Molecular Geometries Within each electron domain, then, there might be more than one molecular geometry.
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Determination of Molecular Geometry 1. Draw Lewis structure. Determine number of electron domains. 2. Determine the electron geometry by minimizing repulsions between electron domains. 3. Draw the arrangement of the bonded atoms and don’t consider the nonbonding electrons to decide on molecular geometry.
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Linear Electron Domain In this domain, there is only one molecular geometry: linear. NOTE: If there are only two atoms in the molecule, the molecule will be linear no matter what the electron domain is.
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Trigonal Planar Electron Domain There are two molecular geometries: Trigonal planar, if all the electron domains are bonding Bent, if one of the domains is a nonbonding pair.
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Tetrahedral Electron Domain There are three molecular geometries: Tetrahedral, if all are bonding pairs Trigonal pyramidal if one is a nonbonding pair Bent if there are two nonbonding pairs
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Angles Nonbonding pairs are physically larger than bonding pairs. Therefore, their repulsions are
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This note was uploaded on 04/25/2008 for the course CHEM 131 taught by Professor Sykora during the Spring '08 term at S. Alabama.

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Chpt9 - Chapter 9 Molecular Geometries and Bonding Theories...

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