9 Molecular Geometries & Bonding Theories

9 Molecular Geometries & Bonding Theories - 1 Chapter 9...

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Unformatted text preview: 1 Chapter 9 Molecular Geometries and Bonding Theories Molecular Shapes • The shape of a molecule plays an important role in its reactivity. •By noting the number of bonding and nonbonding electron pairs we can easily predict the shape of the molecule. 2 2 Molecular Shapes (cont) What Determines the Shape of a Molecule? • Electron pairs, whether they are 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 of the molecule. Electron Domains • We can refer to the electron pairs as electron domains. • In a double or triple bond, all electrons shared between those two atoms are on the same side of the central atom; therefore, they count as one electron domain. The central atom A has four electron domains. 4 3 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. Electron-Domain Geometries The electron-domain geometries for two through six electron domains around a central atom. Fig 9.1 6 4 Electron-Domain Geometries (cont) • 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. Fig 9.6 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. Fig 9.6 8 5 Molecular Geometries (cont) Within each electron domain, then, there might be more than one molecular geometry. Table 9.2 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. Table 9.2 10 6 Example: Predict the electron-domain geometry and the molecular geometry for: PH 3 Molecular geometry: trigonal pyramidal P H H H .. P H H H .. Electron-domain: Tetrahedral Example 2: Predict the electron-domain geometry and The molecular geometry for: SeCl 2 Molecular geometry: bent Electron-domain: Tetrahedral 12 Se Cl Cl .....
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This note was uploaded on 04/18/2008 for the course CHEM 121 taught by Professor Wyzlouzil during the Winter '07 term at Ohio State.

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9 Molecular Geometries & Bonding Theories - 1 Chapter 9...

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