Molecular Geometry and Bonding
Theory
Chapter 9 AP Chemistry
Molecular Geometry
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Molecular Geometry- general shape of a
molecule as determined by the relative
position of the nuclei.
The geometry and size of a molecule helps
to determine it’s chemical behavior.
VSEPR- Valence-Shell-Electron-PairRepulsion model- predicts geometry based
upon e’s around the central atom.
Principles of the VSEPR theory
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Electrons are kept as
far away from one
another as possible –
minimizing e pair
repulsions
Electron pairs are
considered as being
bonding or non-bonding
(lone pairs)
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A multiple bond counts
as a single bonding pair
Electron pair geometry
is described by the
regions of e’s around
the central atom
Molecular geometry is a
consequence of
electron pair geometry.
Predicting Structures VSEPR
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Derive the Lewis Structure to the form AXmEn
A = central atom
X = atoms bonded to the central atom
E = lone pairs of e’s on the central atom
M = # of bonded atoms
N = # of lone pairs
Electron Geometry Linear
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Example
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Electron and Molecular
Geometry Linear
Bond angles 180
Sp Hybrid
Non-polar
More Examples AX2
Electron Geom. Trigonal Planar
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Molecular Geom. Trigonal Planar
bond angles exactly 120 non-polar
Bent bond angles aprox 120 polar molecule
Sp2 hybridized
Electron Geom.Trigonal Planar
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Molecular Geometry: AX3 (3BP or 2BP +
1LP) ex. 3bp NO3-
<>
Examples Cont. 3bp
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BF3 <>
<>
Examples Cont. 2bp + 1 lp
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Ex O3 (ozone)
Electron Geom. Tetrahedral
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Molecular Geom. Tetrahedral bond angles
exactly 109.5 non-polar molecule, Trigonal
pyramidal bond angles aprox. 109.5 polar
molecule, Bent bond angles aprox. 109.5
polar molecule
Sp3 hybridized
Molecular Geometry: AX4 [4BP or (3BP
+ 1LP) or (2BP + 2LP)]
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Electron Geometry: AX4
Tetrahedral
Example
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BrO3F, Perbromyl fluoride
Molecular Geometry: AX3E1
Trigonal Pyramidal
Example
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NF3, Nitrogen trifluoride
Molecular Geometry: AX2E2
Bent/Angular
Example
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H2O, Water, ClOF, Chlorosyl fluoride
Electron Geom. Trigonal Bypyramidal
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Mol. Geom. Trigonal Bypyramidal – bond
angles ax. exactly 108 deg. eq. exactly 120
deg. Non-polar, See-Saw – bond angles ax.
aprox. 108 deg. eq. aprox. 120 deg. Polar, Tshaped - bond angles ax. aprox. 108 deg.
No –eq, Linear – bond angle exactly 180
non-polar.
All sp3d hybridized
Mol geo. Trigonal bipramidal
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AX5 [5BP or (4BP + 1 LP) or (3BP + 2LP) or
(2BP + 3LP)]
5bp
Example
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PCl5(gas phase), Phosphorous
pentachloride
Molecular Geometry:
AX4E1
See-saw
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Example IF2O2-
Molecular Geometry:
AX3E2
T-structure
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Example ClF3
Molecular Geometry:
AX2E3
Linear
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Examole XeF2
Electron Geometry Octahedrial
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Mol geo. Octahedral – bond angle exactly
90 - non-polar, square pyramidal – bond
angle aprox 90- polar, square planar- bond
angle exactly 90 non-polar
Sp3d2 hybridized
Molecular Geometry: AX6
Octahedral
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Example SF6
Molecular Geometry: AX4E1
Pyramidal Planar
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Example XeOF4
Molecular Geometry: AX4E2
Square Planar
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Example XeF4
Bond Angles
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Non-bonding pairs of e’s take up more space
(att. by one nucli) than bonded e pairs
Double and triple bonds take up more space
than single bonds (more e’s)
Volume occupied lone pairs > triple bonds >
double bonds > single bonds
Forces
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Non-bonding pairs exert repulsive forces on
adjacent e pairs and compress angles
Multiple bonds also exert repulsive forces
and compress angles