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Molecular Geometry and Bonding Theories

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  1. Molecular Geometry and Bonding Theories AP Chemistry – Ch 9 Mr. Christopherson

  2. VSEPR Theory • Valence Shell Electron Pair Repulsion Theory • Electron pairs orient themselves around the central atom in order to minimize repulsive forces. They get as far apart from each other as possible. Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  3. Lone pairs repel more strongly than bonding pairs!!! VSEPR Theory • Types of e- Pairs • Bonding pairs - form bonds • Lone pairs - nonbonding electrons Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  4. Bond Angle VSEPR Theory • Lone pairs reduce the bond angle between atoms because they repel more strongly than bonding pairs. Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  5. Know the 8 common shapes & their bond angles! Determining Molecular Shape • Draw the Lewis Diagram. • Count up e- pairs on central atom. • double/triple bonds = ONE pair • Shape is determined by the # of bonding pairs and lone pairs. Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  6. Molecular Shapes AB2 Linear AB3 Trigonal planar AB3E Angular or Bent AB3E Trigonal pyramidal AB2E2 Angular or Bent AB4 Tetrahedral

  7. .. .. .. S O O O C O O S N F O O F F F F F F F F F P S Xe F F F F F F F F The VSEPR Model The Shapes of Some Simple ABn Molecules SO2 Linear Bent Trigonal planar Trigonal pyramidal SF6 Square planar Trigonal bipyramidal Octahedral Brown, LeMay, Bursten, Chemistry The Central Science, 2000, page 305

  8. B : N : : O Bonding and Shape of Molecules Number of Bonds Number of LONE Pairs Covalent Structure Shape Examples -Be- 0 0 0 1 2 2 3 4 3 2 Linear Trigonal planar Tetrahedral Pyramidal Bent BeCl2 BF3 CH4, SiCl4 NH3, PCl3 H2O, H2S, SCl2 C

  9. H 109.5o C H H H 104.5o 107.3o Molecular Geometry 180o 109.5o Trigonal planar Linear Tetrahedral Bent Trigonal pyramidal H2O CH4 PCl3 BeH2 BF3 CO2

  10. H H H C H H C H H H tetrahedral shape of methane H 109.5o C H H H CH4 molecular shape molecular formula structural formula ball-and-stick model tetrahedron

  11. Cl H Cl H Cl H C C Cl H H 109.5o C H H H space-filling model Methane & Carbon Tetrachloride molecular formula structural formula molecular shape ball-and-stick model CH4 CCl4

  12. .. H N C H H H H 107o 109.5o H H O O O O O O O3, ozone .. O H .. 104.5o H CH4, methane NH3, ammonia H2O, water .. lone pair electrons

  13. B A B BeH2 Common Molecular Shapes 2 total 2 bond 0 lone LINEAR 180° Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  14. OCO Examples • CO2 2 total 2 bond 0 lone LINEAR 180° Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  15. B A B B BF3 Common Molecular Shapes 3 total 3 bond 0 lone TRIGONAL PLANAR 120° Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  16. SO2 Common Molecular Shapes 3 total 2 bond 1 lone BENT <120° Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  17. B A B B B CH4 Common Molecular Shapes 4 total 4 bond 0 lone TETRAHEDRAL 109.5° Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  18. NH3 Common Molecular Shapes 4 total 3 bond 1 lone TRIGONAL PYRAMIDAL 107° Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  19. F P F F Examples • PF3 4 total 3 bond 1 lone TRIGONAL PYRAMIDAL 107° Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  20. H2O Common Molecular Shapes 4 total 2 bond 2 lone BENT 104.5° Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  21. Ba PCl5 Be A Be Be Ba Common Molecular Shapes 5 total 5 bond 0 lone TRIGONAL BIPYRAMIDAL 120°/90° Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  22. SF6 B B B A B B B Common Molecular Shapes 6 total 6 bond 0 lone OCTAHEDRAL 90° Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem