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Unformatted text preview: Chapter 9 MOLECULAR GEOMETRY AND BONDING THEORIES Molecular Geometry - the general shape of a molecule, as determined by the relative positions of the atomic nuclei Board discussion of molecules of the general type AB 2 : CO 2 , BeF 2 , SO 2 , and H 2 O VSEPR (The Valence-Shell Electron Pair Repulsion) MODEL A model that accounts for the geometric arrangement of shared and unshared electron pairs around a central atom in terms of the repulsion between electron pairs. The VSEPR Model is used for predicting shapes of molecules. bonding pair (bonding domain) - electron pair that is shared by two atoms in a bond. The VSEPR model counts a single bond, double bond or a triple bond as one “electron domain”. nonbonding pair (nonbonding domain) - an electron pair that remains on one atom and is not shared (lone pair). The VSEPR model counts a lone pair of electrons as one “electron domain”. Rules for Using the VSEPR Model to Predict Molecular Structure 1. Determine the Lewis structure for the molecule or ion. 2. For molecules with resonance structures, use any of the structures to predict the shape of the molecule. 3. Sum the “electron domains” around the central atom. 4. In counting electron pairs, count each single bond and each multiple bond as a single “electron domain”. Count each lone pair on the central atom as an “electron domain”. 5. Arrangement of the pairs is determined by minimizing the electron pair repulsions. (See Figure 9.1 on page 345) 6. Lone pairs require more space than bonding pairs. Give lone pairs as much. room as possible....
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- Fall '11