chem notes 11-26

chem notes 11-26 - -3D shapes: entirely based on v alence s...

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November 26, 2007 Dr. Stevens Gen. Chem. 1 Formal Charges: -total # valence e- – total # non-bonding e- – ½ total # bonding e- -do for each atom in a molecule -neutral molecule: FC must = 0 -ionic molecule: FC must = ion q -for predicting better structures -want fewer small charges rather than more/large charges - –FC more likely on an electronegative atom -ex: NCS-1 -N–C=–S - 5-4- ½ (4) = -1 - 4-0- ½ (8) = 0 - 6-4- ½ (4) = 0 -N+C+S = -1 -N=C=S - 5-6- ½ (2) = -2 - 4-0- ½ (8) = 0 - 6-2- ½ (6) = 1 -N+C+S = -1 -A is better structure b/c smaller charges Chapter 10: Shapes of Molecules 1. use VSEPR theory to predict geometries 2. use VSEPR theory to predict polarity 3. learn hybridization theory to predict bonding and shapes 4. learn MO theory to predict bonding/strength Geometry
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Unformatted text preview: -3D shapes: entirely based on v alence s hell e- p air r epulsion (VSEPR)-VSEPR theory focuses on central atoms-maximizes distances b/w e- pairs (minimize repulsion)-uses e- frameworks-count # of e- regions-spread out equivalently (radially) around central atom-if n=2:-X – A – X-name = linear, angle = 180-ex: CO2-if n=3-name = trigonal planar, angle = 120-ex: COH2 = formaldehyde-if n=4-3D – tripod base with one standing up- triangle: further forward atom – base (right) = forward, point (left) = away-parallel lines creating a triangle: further back atom-ex: CH4-very common: perfect octet-tetrahedral-angle: 109.5-if n=5-flat triangle (on its side), one straight up, one straight down-expanded A (central atom)-ex: PCl5-trigonal bipyramid...
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This note was uploaded on 04/23/2008 for the course CH 151 taught by Professor Stevens during the Fall '08 term at Whitworth University.

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chem notes 11-26 - -3D shapes: entirely based on v alence s...

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