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Ch 6.5 Molecular Geometry

Ch 6.5 Molecular Geometry. VSEPR Theory. Use VSEPR theory Valence-Shell-Electron-Pair Repulsion =the repulsion between electron pairs causes molecular shapes to adjust so that the valence-electron pairs stay as far apart as possible.

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Ch 6.5 Molecular Geometry

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  1. Ch 6.5 Molecular Geometry

  2. VSEPR Theory • Use VSEPR theory • Valence-Shell-Electron-PairRepulsion • =the repulsion between electron pairs causes molecular shapes to adjust so that the valence-electron pairs stay as far apart as possible. • Determined by number of valence electrons of the central atom • 3-D shape is a result of bonded pairs and lone pairs of electrons

  3. Bonding and Shape of Molecules Number of Bonds Number of Unshared Pairs Covalent Structure Shape Examples AB2 0 0 0 1 1 2 3 4 3 2 Linear Trigonal planar Tetrahedral Pyramidal Bent or Angular BeCl2 BF3 CH4, SiCl4 NH3, PCl3 ONF AB3 AB4 AB3E AB2E

  4. .. .. .. S O O O C O O S N C F F O O F F F F F F F F F P S F F F F F F The VSEPR Model SO2 Linear Bent Trigonal planar Trigonal pyramidal AB6 F Tetrahedral Trigonal bipyramidal Octahedral

  5. H H C H H C H H H 109.5o H Tetrahedral geometry Methane CH4

  6. .. .. N H H H N H H 107o H N H H H Ammonia- NH3 N H H H Trigonal Pyramidal geometry

  7. .. .. .. .. O H H .. .. Water –H2O SO2 O H H Bent geometry

  8. F F B B F F F F 120o Boron trifluoride - BF3 Trigonal planar

  9. C O O Carbon dioxide – CO2 O C O Linear

  10. .. .. H N C H H H H 107o 109.5o H H .. O H 104.5o H Bent Pyramidal Tetrahedral

  11. Learning Check Determine the molecular geometry: A. CCl4 B. H2CO

  12. Learning Check Determine the molecular geometry: A. CCl4Tetrahedral B. H2CO

  13. Learning Check Determine the molecular geometry: A. CCl4Tetrahedral B. H2CO Trigonal Planar

  14. Intermolecular Forces • Forces of attraction between molecules • Very weak compared to ionic and metallic bonding. • The strongest occur between polar molecules.

  15. Intermolecular Forces • Dipole: One end slightly positive and one end slightly negative. • Can show the polar nature with an arrow pointing to the more electronegative atom. O H H H Cl

  16. Just because a molecule has a polar bond does not make it a polar molecule. • The bond polarities cancel if they are in opposite directions. • Example: CO2

  17. Attractions Between Molecules • The two weakest attractions between molecules. • Dipole Interactions • When polar molecules are attracted to one another. • Dispersions Forces • Caused by the motion of electrons • Weakest of all interactions.

  18. Hydrogen Bonds • A strong attraction found in hydrogen-containing molecules. • A hydrogen covalently bonded to a very electronegative atom is also weakly bonded to an unshared electron pair of another electronegative atom. • Example • Water

  19. Homework • 6.5 page 210 #33-34, 37-38 NOT 37-42!!

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