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VSEPR

VSEPR. Pronounced vesper…a vespa for her A vest purrs???. Shapes of Molecules. Determined by number of valence electrons of the central atom 3-D shape a result of bonded pairs and lone pairs of electrons Use VSEPR theory (valence-shell-electron-pair repulsion. Using the VSEPR Model.

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VSEPR

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  1. VSEPR • Pronounced vesper…a vespa for her • A vest purrs???

  2. Shapes of Molecules • Determined by number of valence electrons of the central atom • 3-D shape a result of bonded pairs and lone pairs of electrons • Use VSEPR theory (valence-shell-electron-pair repulsion

  3. Using the VSEPR Model 1. Draw the electron-dot structure • Identify the central atom • Count the total number of electron pairs around central atom • Predict the electron shape • Predict the shape of the molecule using the bonding atoms

  4. The AXE system • American General Chemistry textbooks – but for some reason not British ones – adopt the excellent AXmEn system, where A is the central atom, m the number of ligands X, and n the number of nonbonded lone-pairs of electrons, E, about the central atom. • In this system:methane, CH4, is AX4ammonia, H3N:, is AX3E1water, H2O, is AX2E2

  5. Shapes of Molecules Number of electron pairs 2 (= negative charge clouds) Number of bonded atoms 2 Angle 180° Name of shape linear

  6. BeCl2 Be 2 valence electrons .. .. : Cl : Be : Cl : .. .. .. .. : Cl Be Cl : linear, 180° .. .. AX2E0

  7. More Electron Pairs Electron Angle Bonded Name of Pairs Atoms Shape 3 120° 3 trigonal planar AX3E0 3 120° 2 angular or bent AX2E1

  8. Electron Shape with 3 Pairs

  9. BF3 B has 3 valence electrons 120° F trigonal planar B F F AX3E0

  10. SO2 S has 2 bonded atoms , 1 lone pair (electron cloud) 120°, angular .... .. :O:: S:O: S .. OO AX2E1

  11. More Electron Pairs Electron Angle Bonded Name of Pairs Atoms Shape 4 109° 4 tetrahedral AX4E0 4 <109° 3 pyramidal AX3E1 4 <<109° 2 bent, angular AX2E2

  12. Tetrahedral CH4 4 electron Pairs, 4 bonded atoms, 109° H H C H C H H H H H AX4E0

  13. NH3 Pyramidal N has 4 electron pairs, 3 bonded H atoms Shape is called pyramidal .. H : N : H N .. H H H H .. AX3E1

  14. H2O Bent or Angular O has 4 electron pairs, 2 bonded H atoms Shape is called bent or angular, 107.5° .. : O : H O .. H H H .. .. AX2E2

  15. Learning Check Determine the molecular geometry of each of the following: A. CCl4 1) tetrahedral 2) pyramidal 3) angular B. SO3 1) trigonal planar 2) pyramidal 3) angular C. PCl3 1) trigonal planar 2) pyramidal 3) angular

  16. Solution Determine the molecular geometry of each of the following: A. CCl4 1) tetrahedral B. SO3 1) trigonal planar C. PCl3 2) pyramidal

  17. More Electron Pairs Electron Angle Bonded Name of Pairs Atoms Shape 5 120°, 90° 5 trigonal bipyramidal AX5E0 5 <120°, 90° 4 see saw AX4E1 5 90° 3 T shape AX3E2 17

  18. Trigonal bipyramidal PCl5 • 5 electron pairs, 5 bonded atoms AX5E0

  19. See saw SF4 • 5 electron pairs, 4 bonding atoms AX4E1

  20. T shape, ICl3 • 5 electron pairs, 3 bonding atoms AX3E2

  21. More Electron Pairs Electron Angle Bonded Name of Pairs Atoms Shape 6 90° 6 octahedral AX6E0 6 90° 5 square pyramid AX5E1 6 90° 4 Square planar AX4E2 21

  22. Octahedron, SF6 • 6 electron pairs, 6 bonding atoms AX6E0

  23. Square pyramid, ICl5 • 6 electron pairs, 5 bonding atoms AX5E1

  24. Square planar, XeF4 • 6 electron pairs, 4 bonding atoms AX4E2

  25. Now you try!

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