Molecular Shape

1
Molecular Shape

• Valence Shell Electron Pair Repulsion Model
  (VSEPR)
• Most Important Rule 1
• The bond angles around a central atom are those
  which maximize the distance between electron
  pairs in the valence shell of the atom
• Procedure
• Draw Lewis structure
• Count the number of electron pairs (both bonding
  and non-bonding)
• multiple bonds as single pair
• Determine Ideal Molecular Geometry
• Make Corrections to Ideal Geometry
• Nomenclature
• electronic geometry how all electron pairs
  (bonding and non-bonding) are arranged about the
  central atom
• molecular geometry how all bonding pairs are
  arranged about that central atom

2
Electron Pair Geometry
Electron Pairs Angle(s) Name Two
(sp) 180o linear Three (sp2 )
120o trigonal planar Four (sp3)
109.5o tetrahedral Five (sp3d) 120o
90o trigonal bipyramidal Six (sp3d2)
180o octahedral
3
Ideal Molecular Geometry
2 Electron Pairs 2 Bonding, 0 Non-bonding
Linear
4
Ideal Molecular Geometry
3 Electron Pairs 3 Bonding, 0 Non-bonding
Trigonal Planar 2 Bonding, 1 Non-bonding
Bent
5
Ideal Molecular Geometry
4 Electron Pairs 4 Bonding, 0 Non-bonding
Tetrahedral 3 Bonding, 1 Non-bonding
Trigonal Pyramidal 2 Bonding, 2 Non-bonding
Bent
6
Ideal Molecular Geometry
5 Electron Pairs 5 Bonding, 0 Non-bonding
Trigonal Bipyramidal 4 Bonding, 1 Non-bonding
See-Saw 3 Bonding, 2 Non-bonding
T-shaped 2 Bonding, 3 Non-bonding Linear
7
Ideal Molecular Geometry
6 Electron Pairss 6 Bonding, 0 Non-bonding
Octahedral 5 Bonding, 1 Non-bonding
Square Pyramidal 4 Bonding, 2 Non-bonding
Square Planar
8
Ideal Molecular Geometry
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Corrections to Ideal Geometry

• nonbonding domains
• nonbonding domains occupy more space than bonding
  domains
• dont see nonbonding domains, but do see their
  effects
• repulsions NBD-NBD gt NBD-BD gt BD-BD

correction H-N-H bond angle less than ideal
ideal geometry trigonal pyramidal
electronic geometry tetrahedral
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Corrections to Ideal Geometry

• Multiple Bonds
• count as 1 bonding pair
• larger than single bonds take up more room
• O
  O
• C
  C
• Cl Cl Cl
  Cl

ideal geometry trigonal planar
correction Cl-C-Cl bond angle less than ideal
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