Molecular Geometry and Polarization

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Molecular Geometry and Polarization
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Shapes of Molecules

• Valence Shell Electron Pair Repulsion Theory
  (VSEPR)
• Two types of Groups (NH3)
• a. Bonded electrons
• b. Lone Pairs
• VSEPR Valence electron pairs push as far apart
  as possible.

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• 1. Linear (180o)
• BeH2 H2 CO2

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• 2. Trigonal Planar (120o)
• NO3-

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• 3. Tetrahedral (109.5o)
• CH4

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• 4. Trigonal Pyramidal (107o)
• NH3

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• 5. Bent (104.5o)
• H2O

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O
H
H
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• 6. Trigonal Bipyramid (120o, 90o)
• PCl5

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• 7. Octahedral (90o)
• SF6

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Shapes of Molecules

• Ex Multiple Bonds
• N2
• H2CO
• HCN
• SO2

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Shapes of Molecules
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Models Activity

• XeF2
• CH4
• BF3
• BrF5
• SF4
• NO2-
• NH3
• XeF4
• CO2
• H2O
• ClF3
• SF6
• PCl5

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• Predict the molecular geometry of
• SnCl3-
• O3
• SeCl2
• CO32-
• SF4
• IF5
• ClF3
• ICl4-

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Polar Molecules

• 1. Polar molecule Overall, the electrons are
  attracted more to one end of an entire molecule
• 2. Non-Polar Molecule The electrons are spread
  out evenly over the entire molecule
• 3. d-/ d Partial (not full) charges

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• Examples
• H2 H2O
• CH4 BH2Cl (B is the center)

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• H2 H2O
• CH4 BH2Cl

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Polar Molecules

• BeCl2
• NH3
• CO2
• SO2
• SF6
• BCl3
• CH2Cl2

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Hybrid Orbitals

• A mixing of the atomic orbitals (s, p, d, f) of
  the central atom
• Electrons no longer move in the old orbitals, but
  in a new pattern

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• BeF2
• Isolated Be 1s22s2 (Note that all
• electrons are paired)
• To bond Be must unpair some electrons
• Bonded Be 1s22s12p1

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• Be is called an sp hybrid.
• Drawings
• Isolated Be BeF2

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• CH4
• Isolated C 1s22s22p2
• Bonded C 1s22s12p3

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• Isolated C
• Bonded C
• sp3

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Effect of Lone Pairs

• Lone pairs do count towards hybridization
• Ex H2O

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• Try BF3

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• Examples
• CCl4
• NH3
• PF5
• SF6
• XeF4
• BrF3

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Hybrid Orbitals and Multiple Bonds

• sigma (s) bonds single bonds formed by hybrid
  orbitals
• pi (p) bonds double or triple bonds, not formed
  by hybrid orbitals
• H H
• H H CC NN
• H H
• One s bond One s bond plus One s bond plus
• one p bond two p bonds

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• Consider C2H4
• Each C is sp2
• Double bond does not count toward hybridization

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• Consider C2H2
• Each C is sp hybridized
• Two p bonds do not count toward hybridization

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• What is the hybridization and bonding types for
• H2CO? Also, what are the bond angles?

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• What is the hybridization and bonding types for
• acetonitrile (shown)? Also, what are the bond
  angles?
• H
• H - C -CN
• H

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Delocalized Bonding

• Adjacent multiple bonds can overlap.
• Benzene (C6H6)
• All bond lengths are equal

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• Use hybrid orbital theory to explain why all the
  bonds in the NO3- ion are of equal length

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