Chemical Bonding II: Molecular Geometry and Hybridization of ...
Molecular Geometry and Bonding Theory
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Transcript of Molecular Geometry and Bonding Theory
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Molecular Geometry and Bonding Theory
Chapter 9 AP Chemistry
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Molecular Geometry
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-Pair-Repulsion model- predicts geometry based upon e’s around the central atom.
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Principles of the VSEPR theory
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)
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.
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Predicting Structures VSEPR
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
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Electron Geometry Linear
Example Electron and Molecular
Geometry Linear Bond angles 180 Sp Hybrid Non-polar
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More Examples AX2
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Electron Geom. Trigonal Planar
Molecular Geom. Trigonal Planar
bond angles exactly 120 non-polar
Bent bond angles aprox 120 polar molecule Sp2 hybridized
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Electron Geom.Trigonal Planar
Molecular Geometry: AX3 (3BP or 2BP + 1LP) ex. 3bp NO3-
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Examples Cont. 3bp
BF3 <>
<>
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Examples Cont. 2bp + 1 lp
Ex O3 (ozone)
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Electron Geom. Tetrahedral
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
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Molecular Geometry: AX4 [4BP or (3BP + 1LP) or (2BP + 2LP)]
Electron Geometry: AX4Tetrahedral
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Example
BrO3F, Perbromyl fluoride
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Molecular Geometry: AX3E1Trigonal Pyramidal
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Example
NF3, Nitrogen trifluoride
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Molecular Geometry: AX2E2Bent/Angular
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Example
H2O, Water, ClOF, Chlorosyl fluoride
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Electron Geom. Trigonal Bypyramidal
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, T-shaped - bond angles ax. aprox. 108 deg. No –eq, Linear – bond angle exactly 180 non-polar.
All sp3d hybridized
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Mol geo. Trigonal bipramidal
AX5 [5BP or (4BP + 1 LP) or (3BP + 2LP) or (2BP + 3LP)]
5bp
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Example
PCl5(gas phase), Phosphorous pentachloride
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Molecular Geometry:AX4E1See-saw
Example IF2O2-
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Molecular Geometry:AX3E2T-structure
Example ClF3
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Molecular Geometry:AX2E3Linear
Examole XeF2
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Electron Geometry Octahedrial
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
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Molecular Geometry: AX6Octahedral
Example SF6
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Molecular Geometry: AX4E1Pyramidal Planar
Example XeOF4
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Molecular Geometry: AX4E2Square Planar
Example XeF4
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Bond Angles
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
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Forces
Non-bonding pairs exert repulsive forces on adjacent e pairs and compress angles
Multiple bonds also exert repulsive forces and compress angles