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Ch. 6.5 Bonding Theories Molecular Geometry
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POINT > Explain VSEPR Theory
POINT > Use VSEPR and Lewis structures to predict molecular geometry POINT > Identify common molecular shapes POINT > Describe 4 types of intermolecular forces
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POINT > Explain VSEPR Theory
Valence-Shell Electron-Pair Repulsion theory Electron pairs in the valence shell want to be as far apart from each other as possible Molecular shapes adjust so that the valence-electron pairs stay as far apart as possible In VSEPR, we treat double or triple bonds as one set of electrons
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POINT > Explain VSEPR Theory
Example: Methane. What geometric shape will put the e- pairs as far apart as possible? C H
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POINT > Explain VSEPR Theory
Tetrahedral bond angle =109.5◦
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WB CHECK: Draw the Lewis structure for methane. How many bonds in a methane molecule? How many unshared electron pairs? What is the bond angle in a tetrahedron?
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POINT > Explain VSEPR Theory
Unshared pairs must be accounted for when predicting geometric shapes Unshared pairs “repel harder” than bonding pairs Ex. ammonia (NH3)
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POINT > Use VSEPR and Lewis structures to predict molecular geometry
H .. Ex. ammonia (NH3) Lewis structure: **The geometry is determined by the position of the atoms
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POINT > Use VSEPR and Lewis structures to predict molecular geometry
H .. The e- pairs would be arranged in a tetrahedron The atoms are arranged as a pyramid The unshared pair of e- are close to the N and repel the bonding pairs into a narrower angle
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The geometry is pyramidal, the bond angles are 107 ◦
POINT > Use VSEPR and Lewis structures to predict molecular geometry The geometry is pyramidal, the bond angles are 107 ◦
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WB CHECK: How many bonds in a molecule of ammonia? How many unshared electron pairs? What is the bond angle in a pyramidal molecule?
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.. .. O H How about water? Lewis structure:
POINT > Use VSEPR and Lewis structures to predict molecular geometry How about water? Lewis structure: O H
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.. .. O H Again, the e- pairs would be spaced in a tetrahedron
POINT > Use VSEPR and Lewis structures to predict molecular geometry Again, the e- pairs would be spaced in a tetrahedron The atoms are in a geometry called bent The 2 pair of unshared e- force the angle narrower, 105◦ O H
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POINT > Use VSEPR and Lewis structures to predict molecular geometry
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WB CHECK: How many bonds in a molecule of water? How many unshared electron pairs? What is the bond angle in a bent geometry (like water)?
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POINT > Identify common molecular shapes
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WB CHECK: Draw the Lewis structure for CO2. What would the geometry of the atoms be?
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109.5° CH4 Bonds Lone Total Bond angle Example Geometry tetrahedral
Electron pairs around central atom Bonds Lone Total Bond angle Example Geometry 109.5° CH4 tetrahedral
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4 109.5° CH4 107° NH3 Bonds Lone Total Bond angle Example Geometry
Electron pairs around central atom 4 Bonds Lone Total Bond angle Example Geometry 109.5° CH4 tetrahedral 107° NH3 trigonal pyramidal
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3 4 1 109.5° CH4 105° 107° H2O NH3 bent Bonds Lone Total Bond angle
Electron pairs around central atom 3 4 Bonds 1 Lone Total Bond angle Example Geometry 109.5° CH4 tetrahedral 105° 107° H2O NH3 pyramidal bent
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180° CO2 linear 2 3 4 1 109.5° CH4 104.5° 107° H2O NH3 bent Bonds Lone
Electron pairs around central atom 180° CO2 linear 2 3 4 Bonds 1 Lone Total Bond angle Example Geometry 109.5° CH4 tetrahedral 104.5° 107° H2O NH3 pyramidal bent
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2 180° CO2 linear 3 4 1 109.5° CH4 104.5° 107° BF3 H2O NH3 bent
Electron pairs around central atom 2 180° CO2 linear 3 4 Bonds 1 Lone Total Bond angle Example Geometry 109.5° CH4 tetrahedral 104.5° 107° BF3 H2O NH3 pyramidal trigonal planar bent
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2 180° linear 3 4 1 109.5° 120° 104.5° 107° bent CH4 NH3 H2O CO2 BF3
Electron pairs around central atom 2 180° linear 3 4 Bonds 1 Unshared Total Bond angle Example Geometry 109.5° tetrahedral 120° 104.5° 107° pyramidal trigonal planar bent CH4 NH3 H2O CO2 BF3
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2 180° linear 3 4 1 109.5° 120° 104.5° 107° bent trigonal planar Bonds
Electron pairs around central atom 2 180° linear 3 4 Bonds 1 Lone Total Bond angle Example Geometry 109.5° tetrahedral 120° 104.5° 107° pyramidal trigonal planar bent
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a) linear b) bent c) tetrahedral d) trigonal planar e) pyramidal
WB CHECK: A molecule with 3 bonds and 1 unshared pair on the central atom would have a ___________ geometry. a) linear b) bent c) tetrahedral d) trigonal planar e) pyramidal
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WB CHECK: A molecule with 3 bonds and no unshared pair on the central atom would have the ___________ geometry. a) linear b) bent c) tetrahedral d) trigonal planar e) pyramidal
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WB CHECK: A molecule with 2 single bonds and 1 double bond (no unshared pairs) on the central atom would have the ___________ geometry. a) linear b) bent c) tetrahedral d) trigonal planar e) pyramidal
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WB CHECK: A molecule with 1 triple bond and 1 single bond (no unshared pairs) on the central atom would have the ___________ geometry. a) linear b) bent c) tetrahedral d) trigonal planar e) pyramidal
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Homework: Read pages Practice 1a and 1b page 191 #2-3 page 197
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