What determines molecular shape

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Chapter 9 Molecular Geometry and Bonding Theories
What determines molecular shape?
Bond angles angle formed between two adjacent
bonds on the same atom
e.g. CCl4
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Chapter 9 Molecular Geometry and Bonding Theories
What determines molecular shapes?
gt tell us how atoms are physically connected
Lewis Structures
No information regarding the actual 3-D
structure of molecules
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Chapter 9 Molecular Geometry and Bonding Theories
Repulsion of valence electrons gt largest
possible separation of atoms Valence-Shell
Electron-Pair Repulsion Model
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Chapter 9 Molecular Geometry and Bonding Theories
Different ways of depicting 3-D structure
bonds in plane of paper
bond behind the paper plane
"Ball and Stick"
"Spacefilling"
bond in front of the paper plane
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Chapter 9 Molecular Geometry and Bonding Theories
Lewis structures show number of electron domains
nonbonding pair

• Types of Electron Domains
• nonbonding (or "lone") electrons
• single OR double OR triple bonds

Bonding AND non-bonding electron pairs take up
space
bonding pair
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Chapter 9 Molecular Geometry and Bonding Theories
Molecular shape depends on electron domain
geometry

• Lewis Structures tell us
• where bonds (bonding electron pairs) are
• the location of nonbonding electrons

around the central atom
Bonding AND non-bonding electron pairs take up
space
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Chapter 9 Molecular Geometry and Bonding Theories
Possible Electron Domain Geometries
Linear
Trigonal Planar
Tetrahedral
Trigonal Bipyramidal
Octahedral
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Chapter 9 Molecular Geometry and Bonding Theories
Lewis structures ? electron domain geometry ?
molecular geometry
4 electron domains around central atom gt
electron domain geometry Tetrahedral
nonbonding pair
bonding pair
3 bonding 1 non-bonding electron domain
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Chapter 9 Molecular Geometry and Bonding Theories
Lewis structures ? electron domain geometry ?
molecular geometry
4 electron domains around central atom gt
electron domain geometry Tetrahedral
2 non-bonding 2 bonding electron domains
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Chapter 9 Molecular Geometry and Bonding Theories
Lewis structures ? electron domain geometry ?
molecular geometry
3 electron domains around central atom gt
electron domain geometry Trigonal planar
3 bonding electron domains
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Chapter 9 Molecular Geometry and Bonding Theories
Lewis structures ? electron domain geometry ?
molecular geometry
4 electron domains around central atom gt
electron domain geometry Tetrahedral
4 bonding electron domains
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Chapter 9 Molecular Geometry and Bonding Theories
Lewis structures ? electron domain geometry ?
molecular geometry
2 electron domains around central atom gt
electron domain geometry Linear
2 bonding electron domains
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Chapter 9 Molecular Geometry and Bonding Theories
Lewis structures ? electron domain geometry ?
molecular geometry
3 electron domains around central atom gt
electron domain geometry Trigonal planar
1 non-bonding 2 bonding electron domains
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Chapter 9 Molecular Geometry and Bonding Theories
Lewis structures ? electron domain geometry ?
molecular geometry
Molecular Geometry depends on how many of the
electron domains are actually bonds
4 electron domains gt electron domain
geometry Tetrahedral
3 bonds, 1 nonbonding pair gt molecular
geometry Trigonal pyramidal
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Chapter 9 Molecular Geometry and Bonding Theories
Bond angles can be distorted
109.5 o
107 o
104.5 o

• nonbonding electron pairs occupy more volume
  than bonding pairs

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Chapter 9 Molecular Geometry and Bonding Theories
Bond angles can be distorted
125.3 o
111.4 o
125.3 o

• multiple bonds occupy a larger volume than
  single bonds

Volume
Volume
lone pairs gt triple bonds gt double bonds
gt single bonds
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Chapter 9 Molecular Geometry and Bonding Theories
Elements from the 3rd period onward..

• have d -orbitals
• can have an expanded valence shell
• may have more than 4 electron domains
  surrounding them

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Chapter 9 Molecular Geometry and Bonding Theories
Equatorial bond
Axial bond
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Chapter 9 Molecular Geometry and Bonding Theories
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Chapter 9 Molecular Geometry and Bonding Theories
electron domain geometry
molecular geometry
electron domains
TeF6
6
octahedral
90o
90o
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Chapter 9 Molecular Geometry and Bonding Theories
electron domain geometry
molecular geometry
electron domains
H3O
4
tetrahedral
109.5 o
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Chapter 9 Molecular Geometry and Bonding Theories
electron domain geometry
molecular geometry
electron domains
NO2
trigonal planar
3
120o
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Chapter 9 Molecular Geometry and Bonding Theories
electron domain geometry
molecular geometry
electron domains
SO3
trigonal planar
3
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Chapter 9 Molecular Geometry and Bonding Theories
electron domain geometry
molecular geometry
electron domains
SCl2
tetrahedral
4
109.5o
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Chapter 9 Molecular Geometry and Bonding Theories
electron domain geometry
molecular geometry
electron domains
SbI5
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trigonal bipyramidal
120o
90o
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Chapter 9 Molecular Geometry and Bonding Theories
The VESPR model can be extended to larger
molecules e.g. glycine
120 o
109.5 o
predicted bond angles
109.5 o
109.5 o
Trigonal planar
Tetrahedral
Electron-domain geometry
Tetrahedral
Tetrahedral