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Lecture 11 - VSEPR Theory, Molecular Shape 5 Base e - pair geometries will predict 13 Molecular geometries STEPS FOR SUCCESS: 1.draw Lewis 2. bonding pairs 3.lone pairs 4.multiple bonds count as one bonded pair

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Resonance Structures e.g. O 3 (ozone) OOO.. : :

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e.g. SO 3 OOOSOSOSOOOOOOOSOSOSOOOO

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e.g. carbonate ion, CO 3 -2 OOOCOCOCOOOOOOOCOCOCOOOO -2

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Molecules that don’t obey rules Case 2. Incomplete octets FBFFFBFF H - Cl

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Molecules that don’t obey rules Case 3. Expanded Octets e.g. Phosphorus[Ne] 3s 2 3p 3 e.g. Sulfur[Ne] 3s 2 3p 4 e.gXenon[Ne] 3s 2 3p 6 3d sublevel is close in energy to 3p!

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Molecules that don’t obey rules Case 3. Expanded Octets ClF ClFF ClPS ClFF ClF 10 electrons! 12 electrons!

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Molecules that don’t obey rules Case 3. Expanded Octets Xe F F F F : : 12 electrons!

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Predicting Molecular Shapes VSEPR Theory (Valence Shell Electron Pair Repulsion) - Electron clouds repel one another - Terminal atoms move as far apart as possible - Distinctive geometry results

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VSEPR Step 1. - count the number of total electron pairs around the central atom - count # Bonding Pairs -count # Nonbonding or Lone Pairs Step 2. Predict the shape!

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VSEPR ElectronBonds Lone NotationShape Pairs 2 2 0 AX 2 linear 3 3 0 AX 3 trigonal planar 3 2 1 AX 2 Ebent

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AX 2 e.g. CO 2 (Linear) O = C = O bond angle = 180 o

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AX 3 e.g. BF 3 (trigonal planar) bond angle = 120 o B F F F

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AX 2 E e.g. SO 2 (bent) bond angle = 105 o S O O :

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VSEPR ElectronBonds Lone NotationShape Pairs 4 4 0 AX 4 tetrahedral 4 3 1 AX 3 E trigonal pyramidal 4 2 2 AX 2 E 2 bent

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AX 4 e.g. methane C All angles 109.5 o (tetrahedral)

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AX 3 E e.g. ammonia.. 107 o (trigonal pyramidal)

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AX 2 E 2 e.g. water .. 105 o (bent)

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VSEPR ElectronBonds Lone NotationShape Pairs 5 5 0 AX 5 trigonal bipyramidal 5 4 1 AX 4 E see-saw 5 3 2 AX 3 E 2 T-shaped 5 2 3 AX 2 E 3 Linear

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AX 5 Cl ClP Cl ideal angles: 90 o, 120 o (trigonal bipyramidal)

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AX 4 E FFSFFFFSFF : ideal angles: 90 o, 120 o (seesaw)

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AX 3 E 2 Cl Cl I Cl : : ideal angles: 90 o (t-shaped)

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AX 2 E 3 F Xe: F : : angle: 180 o (linear)

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VSEPR ElectronBonds Lone NotationShape Pairss Pairs 6 6 0 AX 6 octahedral 6 5 1 AX 5 E square pyramidal 6 4 2 AX 4 E 2 square planar

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AX 6 FFFSFFFFFFSFFFFF all angles 90 o (octahedral)

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AX 5 E FFFIFF:FFFIFF:FF all angles 90 o (square pyramidal)

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AX 4 E 2 :F XeF : all angles 90 o (square planar)

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