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MOLECULAR STRUCTURE

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  1. MOLECULAR STRUCTURE GEOMETRIES HYBRIDIZATION POLARITY OF MOLECULES SIGMA AND PI BONDS Chapters 10.2-10.3 & 11.1-11.3

  2. Goals & Objectives • See the following Learning Objectives on pages 392 & 419. • Understand these Concepts: • 10.5-8 & 11.1-10. • Master these Skills: • 10.4-5 & 11.1-4.

  3. MOLECULAR STRUCTURE • Draw the Lewis Electron Dot Structure • Predict the electronic geometry • Predict the hybridization on the central atom • Predict the molecular geometry • Predict the polarity of the molecule • Predict the number of sigma bonds • Predict the number of pi bonds

  4. Electronic Geometry • VSEPR Theory • Valence Shell Electron Pair Repulsion Theory • -regions of high electron density about the central atom are as far apart as possible to minimize repulsions • electronic geometries are determined by the number of regions of electron density about the central atom

  5. Electronic Geometry • Regions of Electron • Density Geometry • 2 linear • 3 trigonal planar • 4 tetrahedral • 5 trigonal bipyramidal • 6 octahedral

  6. VALENCE BOND THEORY • explains structures of molecules in terms of the overlap of atomic orbitals to produce bonds between atoms • accounts for electronic geometries by a mathematical combination of atomic orbitals to produce hybrid orbitals that will fit the proposed electronic geometries

  7. Hybrid Orbitals • Electronic GeometryHybridization • linear sp • trigonal planar sp2 • tetrahedral sp3 • trigonal bipyramidal dsp3 • octahedral d2sp3

  8. sp Hybrid Orbitals

  9. The sp hybrid orbitals in gaseous BeCl2. Figure 11.2 atomic orbitals hybrid orbitals orbital box diagrams

  10. The sp hybrid orbitals in gaseous BeCl2(continued). Figure 11.2 orbital box diagrams with orbital contours

  11. sp2 Hybrid Orbitals

  12. The sp2 hybrid orbitals in BF3. Figure 11.3

  13. sp3 Hybrid Orbitals

  14. The sp3 hybrid orbitals in CH4. Figure 11.4

  15. Figure 11.6 The sp3d hybrid orbitals in PCl5.

  16. The sp3d2hybrid orbitals in SF6. Figure 11.7

  17. Molecular Geometry • Electronic Molecular • GeometriesGeometries • linear linear • trigonal planar trigonal planar • angular • tetrahedral tetrahedral • angular • trigonal pyramidal

  18. Figure 10.7 The four molecular shapes of the trigonal bipyramidal electron-group arrangement. PF5 AsF5 SOF4 SF4 XeO2F2 IF4+ IO2F2- XeF2 I3- IF2- ClF3 BrF3

  19. Figure 10.8 The three molecular shapes of the octahedral electron-group arrangement. SF6 IOF5 BrF5 TeF5- XeOF4 XeF4 ICl4-

  20. Molecular Geometry

  21. A summary of common molecular shapes with two to six electron groups. Figure 10.9

  22. Molecular Geometry

  23. Molecular Geometry

  24. Molecular Geometry

  25. Molecular Geometry

  26. POLARITY OF MOLECULES • the polarity of a molecule is the vector sum of the bond polarities of the molecule • the bond polarities will either cancel or not

  27. PROBLEM: From electronegativity (EN) values (button) and their periodic trends, predict whether each of the following molecules is polar and show the direction of bond dipoles and the overall molecular dipole when applicable: PLAN: Draw the shape, find the EN values and combine the concepts to determine the polarity. SOLUTION: (a) NH3 SAMPLE PROBLEM 10.9 Predicting the Polarity of Molecules (a) Ammonia, NH3 (b) Boron trifluoride, BF3 (c) Carbonyl sulfide, COS (atom sequence SCO) The dipoles reinforce each other, so the overall molecule is definitely polar. ENN = 3.0 ENH = 2.1 molecular dipole bond dipoles

  28. SAMPLE PROBLEM 10.10 Predicting the Polarity of Molecules continued (b) BF3 has 24 valence e- and all electrons around the B will be involved in bonds. The shape is AX3, trigonal planar. F (EN 4.0) is more electronegative than B (EN 2.0) and all of the dipoles will be directed from B to F. Because all are at the same angle and of the same magnitude, the molecule is nonpolar. 1200 (c) COS is linear. C and S have the same EN (2.0) but the C=O bond is quite polar(DEN) so the molecule is polar overall.

  29. TYPES OF BONDS • SIGMA bonds • head-on overlap of atomic orbitals • all single bonds are sigma bonds • PI bonds • parallel overlap • the extra bonds

  30. TYPES OF BONDS • single bonds--sigma bonds • double bonds--one sigma and one pi bond • triple bonds-- one sigma and two pi bonds

  31. CH4 • Electronic geometry ____________ • Hybridization on the central atom _______ • Molecular geometry_____________ • Polarity _________________ • Number of sigma bonds ________ • Number of pi bonds __________

  32. CH4

  33. C2H4 • Electronic geometry _________________ • Hybridization on the central atom _______ • Molecular geometry _________________ • Polarity _________________ • Number of sigma bonds ________ • Number of pi bonds __________

  34. C2H4

  35. C2H2 • Electronic geometry _________________ • Hybridization on the central atom _______ • Molecular geometry _________________ • Polarity _________________ • Number of sigma bonds ________ • Number of pi bonds __________

  36. C2H2

  37. CO32- • Electronic geometry _________________ • Hybridization on the central atom _______ • Ionic geometry _________________ • Polarity _________________ • Number of sigma bonds ________ • Number of pi bonds __________

  38. CO32-

  39. BeI2 • Electronic geometry _________________ • Hybridization on the central atom _______ • Molecular geometry _________________ • Polarity _________________ • Number of sigma bonds ________ • Number of pi bonds __________

  40. BCl3 • Electronic geometry _________________ • Hybridization on the central atom _______ • Molecular geometry _________________ • Polarity _________________ • Number of sigma bonds ________ • Number of pi bonds __________

  41. NH3 • Electronic geometry _________________ • Hybridization on the central atom _______ • Molecular geometry _________________ • Polarity _________________ • Number of sigma bonds ________ • Number of pi bonds __________

  42. H2O • Electronic geometry _________________ • Hybridization on the central atom _______ • Molecular geometry _________________ • Polarity _________________ • Number of sigma bonds ________ • Number of pi bonds __________

  43. SCN- • Electronic geometry _________________ • Hybridization on the central atom _______ • Ionic geometry _________________ • Polarity _________________ • Number of sigma bonds ________ • Number of pi bonds __________

  44. PCl5 • Electronic geometry _________________ • Hybridization on the central atom _______ • Molecular geometry _________________ • Polarity _________________ • Number of sigma bonds ________ • Number of pi bonds __________

  45. SF6 • Electronic geometry _________________ • Hybridization on the central atom _______ • Molecular geometry _________________ • Polarity _________________ • Number of sigma bonds ________ • Number of pi bonds __________