Molecular Geometry
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Molecular Geometry
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VSEPR Theory
 VSEPR: Valence Shell Electron Pair
Repulsion
 This theory is useful in predicting the
geometry of a molecule
 Our focus will be to look at the arrangement
of electron pairs around the central atom
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VSEPR Theory
 Assumptions:
– the structure around a given atom is determined
principally by minimizing electron pair
repulsions
– electron pairs (both bonding and nonbonding)
around a given atom should be positioned as far
apart as possible to minimize electron-electron
repulsion
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Valence Shell Electron Pair Repulsion Theory
Nonbonding pairs
Bonding pairs
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Valence Shell Electron Pair Repulsion Theory
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Valence Shell Electron Pair Repulsion Theory
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VSEPR:Four or Fewer Valence-Shell Electron
Pairs Around a Central Atom
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VSEPR:Four or Fewer Valence-Shell Electron
Pairs Around a Central Atom
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Common Bonding Geometries
AB2
AB2
AB3
AB4
•Atoms (B) which are bonded to a central atom (A): ABn
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VSEPR:The Effect of Nonbonding Electrons
and Multiple Bonds on Bond Angles
Nonbonding electron pairs exert greater repulsive forces on adjacent electron pairs
and thus tend to compress the angles between the bonding pairs
Nonbonding electron pairs
109. 5°
Methane (CH4)
107°
Ammonia (NH3)
2 Nonbonding electron pairs
104 .°5
Water (H2O)
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VSEPR: Molecules with No Single Central Atom
Tetrahedral
Trigonal Planar
Bent
H
H
O
C
C
..
..O
H
H
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Example: Determine the molecular
geometry of CO2
O
C
The central atom (C) has
2 bonding pairs, 0 lone pairs
Shape is linear,
bond angle = 180
O=C=O
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O