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Molecular Shapes and Hybrid Orbitals
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Why is molecular shape important?
The shape of a molecule contributes to its properties and behavior Changing the shape can change how the molecule functions Extremely important in biological processes: Enzymes Cancer-treatment drugs
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What accounts for the shape of a molecule?
Valence-Shell Electron-Pair Repulsion Theory (VSEPR Theory), pronounced “vesper”: atoms align themselves to maximize the distance between the valence electron pairs
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Shapes you need to know…
Start with… Example # atoms bonded to central atom # lone pairs on central atom Molecular Shape Molecular Polarity linear F2 CO2 trigonal planar BF3 NO2– tetrahedral CH4 NH3 H2O trigonal bipyramidal PF5
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Molecular Polarity Not the same thing as bond polarity
With molecular polarity, it’s all about symmetry and whether the molecule has a dipole moment.
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Molecular Polarity Two nonpolar molecule requirements:
1. Identical atoms bonded to central atom 2. No lone pairs of electrons on central atom
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Shapes you need to know…
Start with… Example # atoms bonded to central atom # lone pairs on central atom Molecular Shape Molecular Polarity linear F2 CO2 trigonal planar BF3 NO2– tetrahedral CH4 NH3 H2O trigonal bipyramidal PF5
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Why do atoms bond? Diagram from Pearson Education 2014.
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Bonding often brings atoms to a lower energy state
Why do atoms bond? Bonding often brings atoms to a lower energy state Diagram from Pearson Education 2014.
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Hybrid Orbitals Atoms share electrons so they can fill their outermost s & p orbitals Orbitals overlap to form a bond
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Hybrid Orbitals – Example #1
Draw the orbital notation diagram for carbon. Carbon’s “standard” electron configuration: Two half-filled p orbitals... so how does carbon form four bonds? Hybridization: a theory that helps explain the shapes of some molecules
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Hybrid Orbitals – Example #1
Carbon hybridizes its valence s and p orbitals Move an electron from the 2s to the 2p orbital We call these sp3 hybrid orbitals (1 s orbital and 3 p orbitals mix)
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Hybrid Orbitals sp3 hybridization leads to a tetrahedral shape (bond angles 109.5°)
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Hybrid Orbitals – Example #2
Draw the orbital notation diagram for boron.
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Hybrid Orbitals – Example #2
Boron hybridizes its valence s and p orbitals Move an electron from the 2s to the 2p orbital We call these sp2 hybrid orbitals (1 s orbital and 2 p orbitals mix)
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Hybrid Orbitals sp2 hybridization leads to a trigonal planar shape (bond angles 120°)
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Hybrid Orbitals – Example #3
Draw the orbital notation diagram for beryllium.
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Hybrid Orbitals – Example #3
Beryllium hybridizes its valence s and p orbitals Move an electron from the 2s to the 2p orbital We call these sp hybrid orbitals (1 s orbital and 1 p orbital mix)
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Hybrid Orbitals sp hybridization leads to a linear shape (180° bond angle)
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Bond Strength and Length
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Sigma and Pi Bonds
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Shape #1 – Linear F2 Lewis structure CO2 Lewis structure
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Shape #2 – Trigonal Planar
BF3 Lewis structure: NO2– Lewis structure:
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Shape #3 – Tetrahedral CH4 Lewis structure: NH3 Lewis structure:
H2O Lewis dot structure:
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