Molecular Geometry and 3D Structures of Molecules

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Molecular Geometry and 3D Structures of Molecules
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Methane Lewis Dot Structure
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Sites on an atom

• A site is something that takes up space around
  the atom.
• Attached atoms
• Unshared pairs of electrons
• Total sites attached atoms unshared
  pairs

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Sites in Methane

• Carbon is central atom
• 4 atoms (H) attached
• no unshared pairs
• sites 4 0 4
• 4 sites

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VSEPR Theory

• Electrons repel
• Will move as far apart as possible in 3
  dimensions
• Actually electron clouds that repel.
• Attached atoms positioned by repulsion of
  electrons clouds bonded to.

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Methane Summary

• clouds arrange tetrahedrally
• clouds 109.5o apart
• Shape is tetrahedral

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Methane ball and stick
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3D representation of methane

• Wedge is coming out of plane of paper
• dash behind
• compare to ball and stick

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Comparison of Methane Structures
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Space filling model of methane
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Summary sheet
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Ammonia Lewis Dot Structure
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Sites in Ammonia

• 3 attached atoms
• 1 unshared pair
• total of 4 sites
• Clouds tetrahedral

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Ammonia Ball and Stick
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3D Representation of Ammonia

• Clouds still tetrahedral
• one cloud has unshared pair
• invisible cloud
• repels more strongly than bonds
• pushes bonds together
• bond angle 107.7
• trigonal pyramidal

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Comparison of Ammonia Structures
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Ammonia space fill
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Summary sheet
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Water Lewis Dot Structure
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Sites in Water

• 2 attached atoms
• 2 unshared pairs
• 4 sites
• Clouds tetrahedral

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Water Ball and Stick
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3D Representation of Water

• Clouds still tetrahedral
• two clouds have unshared pairs
• invisible clouds
• repel more strongly than bonds
• push bonds together
• bond angle 105
• bent

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Comparison of Water Structures
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Water Space Fill
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Summary sheet
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HCl Lewis Dot Structure
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Sites in HCl

• 1 attached atom
• 3 unshared pairs
• 4 sites
• Clouds tetrahedral

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HCl Ball and Stick
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3D Representation of HCl

• Clouds still tetrahedral
• three clouds have unshared pairs
• invisible clouds
• bond angle 180
• linear

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Comparison of HCl Structures
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HCl Space Fill
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Summary sheet
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CH2O Lewis Dot Structure
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Sites in CH2O

• 3 attached atoms
• 0 unshared pairs
• 3 sites
• Clouds trigonal planar

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CH2O Ball and Stick
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3D Representation of CH2O

• clouds go to corners of equilateral triangle
• bond angle 120
• trigonal planar

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Comparison of CH2O Structures
Since planar, both structures are the same.
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CH2O Space Fill
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Summary sheet
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SO2 Lewis Dot Structure
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Sites in SO2

• 2 attached atoms
• 1 unshared pairs
• 3 sites
• Clouds trigonal planar

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SO2 Ball and Stick
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3D Representation of SO2

• Clouds go to corners of equilateral triangle
• unshared pair is invisible cloud
• bond angle between 105 and 120
• bent

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Comparison of SO2 Structures
Since bent, both structures are the same.
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SO2 Space Fill
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Summary sheet
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SO2 Lewis Dot StructureDouble bonded oxygen
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Sites on O in SO2

• 1 attached atoms
• 2 unshared pairs
• 3 sites
• Clouds trigonal planar

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3D Representation of SO2

• Clouds go to corners of equilateral triangle
• unshared pairs are invisible clouds
• bond angle 180
• linear around double bound oxygen

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Comparison of SO2 Structures
Linear around double bonded O
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Summary sheet
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CO2 Lewis Dot Structure
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Sites in CO2

• 2 attached atoms
• 0 unshared pairs
• 2 sites
• Clouds linear

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CO2 Ball and Stick
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3D Representation of CO2

• Clouds linearly arranged.
• bond angle 180
• linear

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Comparison of CO2 Structures
Since linear, both structures are the same.
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CO2 Space Fill
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Summary sheet
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N2 Lewis Dot Structure
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Sites in N2

• 1 attached atom
• 1 unshared pair
• 2 sites
• Clouds linear

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N2 Ball and Stick
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3D Representation of N2

• Clouds linearly arranged.
• bond angle 180
• linear

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Comparison of N2 Structures
Since linear, both structures are the same.
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N2 Space Fill
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Summary sheet