Chem1201PReviewCh9

Chem1201PReviewCh9 - Chemistry 1201 Review/Preview Chapter...

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Chemistry 1201 Review/Preview Chapter Nine Review Guide Dr. Saundra McGuire Spring 2007 Director, Center for Academic Success Adj. Prof., Dept. of Chemistry Molecular Geometry and Bonding Theories I. Molecular Shapes The three dimensional shape of a molecule is determined from the number of electron domains (atoms and nonbonding pairs of electrons) connected to the central atom. The steps involved in determining the shape of a molecule are written below: 1. Draw the correct electron dot structure. 2. Count the number of electron domains (atoms plus lone pairs) around the central atom. 3. Determine the electron arrangement around the central atom. (This is the shape of the molecule if there are no lone pairs.) 4. If lone pairs are present, describe the shape of the molecule ignoring the position(s) occupied by any lone pairs See figures 9.1, 9.2, 9.3, and 9.4 for pictures of the possible shapes of molecules. II. The VSEPR Model The Valence Shell Electron Pair Repulsion Model, or VSEPR (pronounced “vesper”) is based on the concept that the valence electrons in a molecule will repel each other. The shape that a molecule (or ion) assumes is the one that allows the valence electrons to be as far apart as possible. A. Determining the Molecular Shape To correctly determine molecular shape we must always begin with a correct Lewis structure that will tell us how many valence electrons are in the molecule. (If we start with an incorrect Lewis structure, we will most probably assign the molecule an incorrect shape. Always exercise extreme care when drawing Lewis structures to make sure they are correct.) When we have the correct dot structure, we can determine the number of electron domains (the number of electron groups around the central atoms of the molecule). The steps to follow in determining the shape of a molecule are summarized below. 1.
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This note was uploaded on 03/23/2011 for the course CHE 1201 taught by Professor Staff during the Summer '09 term at UC Davis.

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Chem1201PReviewCh9 - Chemistry 1201 Review/Preview Chapter...

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