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Lecture 11 - VSEPR Theory, Molecular Shape

Lecture 11 - VSEPR Theory, Molecular Shape. 5 Base e - pair geometries will predict 13 Molecular geometries STEPS FOR SUCCESS: draw Lewis bonding pairs lone pairs multiple bonds count as one bonded pair. Resonance Structures. e.g. O 3 (ozone). :. :. O O O O O O. O O O

harlan-briggs
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Lecture 11 - VSEPR Theory, Molecular Shape

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

  2. Resonance Structures .. .. .. .. .. .. e.g. O3 (ozone) : : O O O O O O .. .. .. ..

  3. O O O S O S O S O O O O e.g. SO3

  4. -2 -2 -2 O O O C O C O C O O O O e.g. carbonate ion, CO3-2

  5. Molecules that don’t obey rules .. : : F B F F Case 2. Incomplete octets .. .. : H - Cl : .. .. : : ..

  6. Molecules that don’t obey rules Case 3. Expanded Octets e.g. Phosphorus [Ne] 3s2 3p3 e.g. Sulfur [Ne] 3s2 3p4 e.g Xenon [Ne] 3s2 3p6 3d sublevel is close in energy to 3p!

  7. Molecules that don’t obey rules Cl F Cl F F Cl P S Cl F F Cl F Case 3. Expanded Octets 10 electrons! 12 electrons!

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

  9. 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

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

  11. VSEPR Electron Bonds Lone Notation Shape Pairs Pairs 2 2 0 AX2 linear 3 3 0 AX3 trigonal planar 3 2 1 AX2E bent

  12. AX2 e.g. CO2 (Linear) O = C = O bond angle = 180o

  13. AX3e.g. BF3 F (trigonal planar) bond angle = 120o B F F

  14. AX2Ee.g. SO2 O (bent) bond angle = 105o : S O

  15. VSEPR Electron BondsLone Notation Shape Pairs Pairs 4 4 0 AX4 tetrahedral 4 3 1 AX3E trigonal pyramidal 4 2 2 AX2E2 bent

  16. AX4e.g. methane (tetrahedral) All angles 109.5o H C H H H

  17. AX3E e.g. ammonia (trigonal pyramidal) .. N H H 107o H

  18. AX2E2 e.g. water (bent) H H .. 105o O .. H

  19. VSEPR Electron Bonds Lone Notation Shape Pairs Pairs 5 5 0 AX5 trigonal bipyramidal 5 4 1 AX4E see-saw 5 3 2 AX3E2 T-shaped 5 2 3 AX2E3 Linear

  20. AX5 (trigonal bipyramidal) Cl Cl Cl P Cl Cl ideal angles: 90o, 120o

  21. AX4E (seesaw) F F S F F : ideal angles: 90o, 120o

  22. AX3E2 (t-shaped) Cl Cl I Cl : : ideal angles: 90o

  23. AX2E3 (linear) F Xe : F : : angle: 180o

  24. VSEPR Electron BondsLone Notation Shape Pairss Pairs 6 6 0 AX6 octahedral 6 5 1 AX5E square pyramidal 6 4 2 AX4E2 square planar

  25. AX6 (octahedral) F F F S F F F all angles 90o

  26. AX5E (square pyramidal) F F F I F F : all angles 90o

  27. AX4E2 : F F Xe F F : (square planar) all angles 90o

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