Chemical bonding II

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Chemical bonding II

  1. 1. Chemical Bonding II: Molecular Geometry and Hybridization of Atomic Orbitals Chapter 10 Copyright © The McGraw-Hill Companies, Inc.  Permission required for reproduction or display. PowerPoint Lecture Presentation by J. David Robertson University of Missouri
  2. 2. 10.1
  3. 3. Valence shell electron pair repulsion (VSEPR) model: Predict the geometry of the molecule from the electrostatic repulsions between the electron (bonding and nonbonding) pairs. AB 2 2 0 10.1 Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry linear linear B B
  4. 4. 10.1 Cl Cl Be 2 atoms bonded to central atom 0 lone pairs on central atom
  5. 5. AB 2 2 0 linear linear VSEPR AB 3 3 0 10.1 Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry trigonal planar trigonal planar
  6. 6. 10.1
  7. 7. AB 2 2 0 linear linear VSEPR 10.1 AB 4 4 0 Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry AB 3 3 0 trigonal planar trigonal planar tetrahedral tetrahedral
  8. 8. 10.1
  9. 9. AB 2 2 0 linear linear VSEPR 10.1 AB 4 4 0 tetrahedral tetrahedral AB 5 5 0 Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry AB 3 3 0 trigonal planar trigonal planar trigonal bipyramidal trigonal bipyramidal
  10. 10. 10.1
  11. 11. AB 2 2 0 linear linear VSEPR 10.1 AB 4 4 0 tetrahedral tetrahedral AB 6 6 0 Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry AB 3 3 0 trigonal planar trigonal planar AB 5 5 0 trigonal bipyramidal trigonal bipyramidal octahedral octahedral
  12. 12. 10.1
  13. 13. 10.1
  14. 14. bonding-pair vs. bonding pair repulsion lone-pair vs. lone pair repulsion lone-pair vs. bonding pair repulsion > >
  15. 15. VSEPR AB 3 3 0 trigonal planar trigonal planar AB 2 E 2 1 10.1 Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry trigonal planar bent
  16. 16. VSEPR AB 3 E 3 1 AB 4 4 0 tetrahedral tetrahedral 10.1 Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry tetrahedral trigonal pyramidal
  17. 17. VSEPR AB 4 4 0 tetrahedral tetrahedral 10.1 AB 2 E 2 2 2 Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry AB 3 E 3 1 tetrahedral trigonal pyramidal tetrahedral bent H O H
  18. 18. VSEPR 10.1 AB 5 5 0 trigonal bipyramidal trigonal bipyramidal AB 4 E 4 1 Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry trigonal bipyramidal distorted tetrahedron
  19. 19. VSEPR 10.1 AB 5 5 0 trigonal bipyramidal trigonal bipyramidal AB 3 E 2 3 2 Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry AB 4 E 4 1 trigonal bipyramidal distorted tetrahedron trigonal bipyramidal T-shaped Cl F F F
  20. 20. VSEPR 10.1 AB 5 5 0 trigonal bipyramidal trigonal bipyramidal AB 2 E 3 2 3 Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry AB 4 E 4 1 trigonal bipyramidal distorted tetrahedron AB 3 E 2 3 2 trigonal bipyramidal T-shaped trigonal bipyramidal linear I I I
  21. 21. VSEPR 10.1 AB 5 E 5 1 Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry AB 6 6 0 octahedral octahedral octahedral square pyramidal Br F F F F F
  22. 22. VSEPR 10.1 AB 4 E 2 4 2 Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry AB 6 6 0 octahedral octahedral AB 5 E 5 1 octahedral square pyramidal octahedral square planar Xe F F F F
  23. 23. 10.1
  24. 24. Predicting Molecular Geometry <ul><li>Draw Lewis structure for molecule. </li></ul><ul><li>Count number of lone pairs on the central atom and number of atoms bonded to the central atom. </li></ul><ul><li>Use VSEPR to predict the geometry of the molecule. </li></ul>AB 2 E bent AB 4 E distorted tetrahedron 10.1 What are the molecular geometries of SO 2 and SF 4 ? S O O S F F F F
  25. 25. Dipole Moments and Polar Molecules 10.2 electron rich region electron poor region  = Q x r Q is the charge r is the distance between charges 1 D = 3.36 x 10 -30 C m H F  
  26. 26. 10.2
  27. 27. 10.2
  28. 28. 10.2 dipole moment polar molecule no dipole moment nonpolar molecule dipole moment polar molecule no dipole moment nonpolar molecule Which of the following molecules have a dipole moment? H 2 O, CO 2 , SO 2 , and CH 4 O H H S O O C O O C H H H H
  29. 29. 10.2 Does CH 2 Cl 2 have a dipole moment?
  30. 30. 10.2
  31. 31. 10.2 Chemistry In Action: Microwave Ovens
  32. 32. Valence bond theory – bonds are formed by sharing of e - from overlapping atomic orbitals. Sharing of two electrons between the two atoms. 10.3 Bond Dissociation Energy Bond Length H 2 F 2 436.4 kJ/mole 150.6 kJ/mole 74 pm 142 pm Overlap Of 2 1s 2 2p How does Lewis theory explain the bonds in H 2 and F 2 ?
  33. 33. 10.4
  34. 34. Change in electron density as two hydrogen atoms approach each other. 10.3
  35. 35. Valence Bond Theory and NH 3 N – 1s 2 2s 2 2p 3 3 H – 1s 1 If use the 3 2p orbitals predict 90 0 Actual H-N-H bond angle is 107.3 0 10.4 If the bonds form from overlap of 3 2p orbitals on nitrogen with the 1s orbital on each hydrogen atom, what would the molecular geometry of NH 3 be?
  36. 36. Hybridization – mixing of two or more atomic orbitals to form a new set of hybrid orbitals. <ul><li>Mix at least 2 nonequivalent atomic orbitals ( e.g. s and p). Hybrid orbitals have very different shape from original atomic orbitals. </li></ul><ul><li>Number of hybrid orbitals is equal to number of pure atomic orbitals used in the hybridization process. </li></ul><ul><li>Covalent bonds are formed by: </li></ul><ul><ul><li>Overlap of hybrid orbitals with atomic orbitals </li></ul></ul><ul><ul><li>Overlap of hybrid orbitals with other hybrid orbitals </li></ul></ul>10.4
  37. 37. 10.4
  38. 38. 10.4
  39. 39. 10.4 Predict correct bond angle
  40. 40. Formation of sp Hybrid Orbitals 10.4
  41. 41. Formation of sp 2 Hybrid Orbitals 10.4
  42. 42. # of Lone Pairs + # of Bonded Atoms Hybridization Examples 2 3 4 5 6 sp sp 2 sp 3 sp 3 d sp 3 d 2 BeCl 2 BF 3 CH 4 , NH 3 , H 2 O PCl 5 SF 6 Count the number of lone pairs AND the number of atoms bonded to the central atom 10.4 How do I predict the hybridization of the central atom?
  43. 43. 10.4
  44. 44. 10.5
  45. 45. 10.5
  46. 46. 10.5 Sigma bond (  ) – electron density between the 2 atoms Pi bond (  ) – electron density above and below plane of nuclei of the bonding atoms
  47. 47. 10.5
  48. 48. 10.5
  49. 49. 10.5
  50. 50. Sigma (  ) and Pi Bonds (  ) Single bond 1 sigma bond Double bond 1 sigma bond and 1 pi bond Triple bond 1 sigma bond and 2 pi bonds  bonds = 6 + 1 = 7  bonds = 1 10.5 How many  and  bonds are in the acetic acid (vinegar) molecule CH 3 COOH? C H H C H O O H
  51. 51. Molecular orbital theory – bonds are formed from interaction of atomic orbitals to form molecular orbitals. No unpaired e - Should be diamagnetic 10.6 O O Experiments show O 2 is paramagnetic
  52. 52. Energy levels of bonding and antibonding molecular orbitals in hydrogen (H 2 ). A bonding molecular orbital has lower energy and greater stability than the atomic orbitals from which it was formed. An antibonding molecular orbital has higher energy and lower stability than the atomic orbitals from which it was formed. 10.6
  53. 53. 10.6
  54. 54. 10.6
  55. 55. 10.6
  56. 56. 10.6
  57. 57. <ul><li>The number of molecular orbitals (MOs) formed is always equal to the number of atomic orbitals combined. </li></ul><ul><li>The more stable the bonding MO, the less stable the corresponding antibonding MO. </li></ul><ul><li>The filling of MOs proceeds from low to high energies. </li></ul><ul><li>Each MO can accommodate up to two electrons. </li></ul><ul><li>Use Hund’s rule when adding electrons to MOs of the same energy. </li></ul><ul><li>The number of electrons in the MOs is equal to the sum of all the electrons on the bonding atoms. </li></ul>10.7 Molecular Orbital (MO) Configurations
  58. 58. 10.7 bond order ½ 1 0 ½ bond order = 1 2 Number of electrons in bonding MOs Number of electrons in antibonding MOs ( - )
  59. 59. 10.7
  60. 60. Delocalized molecular orbitals are not confined between two adjacent bonding atoms, but actually extend over three or more atoms. 10.8
  61. 61. Electron density above and below the plane of the benzene molecule. 10.8
  62. 62. 10.8
  63. 63. Chemistry In Action: Buckyball Anyone? 10.8

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