1. CHE 106 No. 1 Chapter Nine Copyright © James T. Spencer 1995 - 1997 All Rights Reserved

2. CHE 106 No. 2 Molecular Shapes and Bonding Molecular Shape guides chemical reactivity, especially biological. Molecular Shape guides chemical reactivity, especially biological. Why is water bent while CO 2 is linear? Why is water bent while CO 2 is linear? Why is ClF 3 T-shaped while NF 3 is pyramidal? Why is ClF 3 T-shaped while NF 3 is pyramidal? Why is CF 4 tetrahedral while XeF 4 is planar? Why is CF 4 tetrahedral while XeF 4 is planar? C O Cl N

3. CHE 106 No. 3 Molecular Geometry l Definitions: » Bond Distance - the distance (usually in either Å or pm) between two bonded atoms » Bond Angles - the angle formed between three bonded atoms A A A bondangle bonddistance

4. CHE 106 No. 4 Valence-Shell Electron Pair Repulsion Theory (VSEPR) l Electrons repel one another (same charge). l Arrange electron pairs around atoms in a molecule so as to maximize the distance between them (placing them as far apart as possible while still attached to the central atom). Minimize repulsions! l Use AXE Notation to help keep track: A = central atom X = number of bond pairs of electrons E = number of “lone” (unshared) pairs of electrons

5. CHE 106 No. 5 l 1st Approximation, assume bond and lone electron pairs are equivalent. l Derive “Parent” Structures for various numbers of electron pairs around the central atom. (2 - 6 pairs). l Consider “balloon” model. l At the end, differentiate between bond and lone electron pairs by placing non-central atoms Valence-Shell Electron Pair Repulsion Theory (VSEPR)

6. CHE 106 No. 6 Valence-Shell Electron Pair Repulsion Theory (VSEPR) 2 Electron Pairs - AX 2 E 0

7. CHE 106 No. 7 Valence-Shell Electron Pair Repulsion Theory (VSEPR) 3 Electron Pairs AX 3 E 0

8. CHE 106 No. 8 Valence-Shell Electron Pair Repulsion Theory (VSEPR) 4 Electron Pairs AX 4 E 0

9. CHE 106 No. 9 Valence-Shell Electron Pair Repulsion Theory (VSEPR) 5 Electron Pairs AX 5 E 0

10. CHE 106 No. 10 Valence-Shell Electron Pair Repulsion Theory (VSEPR) 5 Electron Pairs AX 5 E 0

11. CHE 106 No. 11 Valence-Shell Electron Pair Repulsion Theory (VSEPR) 6 Electron Pairs AX 6 E 0

12. CHE 106 No. 12 VSEPR l Arrange electron pairs so as to maximize the distance between them. AXEShapeName AX 1 E 0 Linear AX 2 E 0 Linear AX 3 E 0 Trigonal Planar AX 4 E 0 Tetrahedron = electron pair

13. CHE 106 No. 13 VSEPR l Arrange electron pairs so as to maximize the distance between them. AXEShapeName AX 1 E 0 Linear AX 2 E 0 Linear AX 3 E 0 Trigonal Planar AX 4 E 0 Tetrahedron = electron pair

14. CHE 106 No. 14 VSEPR l Arrange electron pairs so as to maximize the distance between them. AXEShapeName AX 1 E 0 Linear AX 2 E 0 Linear AX 3 E 0 Trigonal Planar AX 4 E 0 Tetrahedron = electron pair

15. CHE 106 No. 15 AXEShapeName AX 1 E 0 Linear AX 2 E 0 Linear AX 3 E 0 Trigonal Planar AX 4 E 0 Tetrahedron VSEPR l Arrange electron pairs so as to maximize the distance between them. = electron pair

16. CHE 106 No. 16 AXEShapeName AX 5 E 0 Trigonal bipyramid bipyramid AX 6 E 0 Octahedron VSEPR l Arrange electron pairs so as to maximize the distance between them. = electron pair

17. CHE 106 No. 17 AXEShapeName AX 5 E 0 Trigonal bipyramid bipyramid AX 6 E 0 Octahedron VSEPR l Arrange electron pairs so as to maximize the distance between them. = electron pair

18. CHE 106 No. 18 Closer Look at Structures LinearLinear Trigonal PlanarTetrahedral 180° 180° 120° 109.5° “flat”molecule “tripod”molecule

19. CHE 106 No. 19 Closer Look at Structures Octahedron 120° 90° 180° 180° 90° Trigonal Bipyramid Axial Positions Equatorial Positions

20. CHE 106 No. 20 VSEPR l Summary : – The best electron pair arrangement minimizes electron-electron repulsions. – Both bonding electron pairs and unshared (non-bonding) electron pairs are arranged to minimize repulsions. – Use AXE notation to determine actual molecular geometries.

21. CHE 106 No. 21 l Determine Lewis structure l Determine number of electron pairs around the central atom l Determine AXE notation l Assign structure based upon parent structure - minimizing repulsions l Determine any distortions of bond angles Valence-Shell Electron Pair Repulsion Theory (VSEPR)

22. CHE 106 No. 22 VSEPR and AXE : A = central atom; X = number of bond pairs of electrons; E = number of “lone” (unshared) pairs of electrons AXEShapeName AX 1 E 0 Linear AX 2 E 0 Linear AX 1 E 1 Linear 2 Pairs

23. CHE 106 No. 23 VSEPR and AXE : A = central atom; X = number of bond pairs of electrons; E = number of “lone” (unshared) pairs of electrons AXEShapeName AX 1 E 0 Linear AX 2 E 0 Linear AX 1 E 1 Linear 2 Pairs

24. CHE 106 No. 24 VSEPR and AXE : A = central atom; X = number of bond pairs of electrons; E = number of “lone” (unshared) pairs of electrons : : AXEShapeName AX 3 E 0 Trigonal Planar AX 2 E 1 Bent AX 1 E 2 Linear Trigonal Planar Angle = 120° 3 Pairs

25. CHE 106 No. 25 VSEPR and AXE : A = central atom; X = number of bond pairs of electrons; E = number of “lone” (unshared) pairs of electrons : : AXEShapeName AX 3 E 0 Trigonal Planar AX 2 E 1 Bent AX 1 E 2 Linear Trigonal Planar Angle = 120° 3 Pairs

26. CHE 106 No. 26 VSEPR and AXE : A = central atom; X = number of bond pairs of electrons; E = number of “lone” (unshared) pairs of electrons : : AXEShapeName AX 3 E 0 Trigonal Planar AX 2 E 1 Bent AX 1 E 2 Linear Trigonal Planar Angle = 120° 3 Pairs

27. CHE 106 No. 27 Nonbonding Electrons and Multiple Bonds l Non-bonding electron pairs exert greater repulsive forces on adjacent electron pairs and, therefore, compress the angles between the bond pairs. l Electrons in multiple bonds exert greater repulsive forces on adjacent electron pairs and, therefore, compress the angles between the bond pairs (similar to nonbonding electrons). 109.5° 104.5° 107°

28. CHE 106 No. 28 VSEPR and AXE : A = central atom; X = number of bond pairs of electrons; E = number of “lone” (unshared) pairs of electrons : : Tetrahedral Angle = 109.5° AXEShapeName AX 4 E 0 Tetrahedron AX 3 E 1 Trigonal Pyramidal AX 2 E 2 Bent 4 Pairs

29. CHE 106 No. 29 VSEPR and AXE : A = central atom; X = number of bond pairs of electrons; E = number of “lone” (unshared) pairs of electrons : : Tetrahedral Angle = 109.5° AXEShapeName AX 4 E 0 Tetrahedron AX 3 E 1 Trigonal Pyramidal AX 2 E 2 Bent 4 Pairs

30. CHE 106 No. 30 VSEPR and AXE : A = central atom; X = number of bond pairs of electrons; E = number of “lone” (unshared) pairs of electrons : : Tetrahedral Angle = 109.5° AXEShapeName AX 4 E 0 Tetrahedron AX 3 E 1 Trigonal Pyramidal AX 2 E 2 Bent 4 Pairs

31. CHE 106 No. 31 VSEPR and AXE A = central atom; X = number of bond pairs of electrons; E = number of “lone” (unshared) pairs of electrons Angles = 120° and 90° : : : : : : AXEShapeName AX 5 E 0 Trigonal Bipyramid AX 4 E 1 See-Saw AX 3 E 2 T-Shaped AX 2 E 3 Linear 5 Pairs

32. CHE 106 No. 32 VSEPR and AXE A = central atom; X = number of bond pairs of electrons; E = number of “lone” (unshared) pairs of electrons Angles = 120° and 90° : : : : : : AXEShapeName AX 5 E 0 Trigonal Bipyramid AX 4 E 1 See-Saw AX 3 E 2 T-Shaped AX 2 E 3 Linear 5 Pairs

33. CHE 106 No. 33 VSEPR and AXE A = central atom; X = number of bond pairs of electrons; E = number of “lone” (unshared) pairs of electrons Angles = 120° and 90° : : : : : : AXEShapeName AX 5 E 0 Trigonal Bipyramid AX 4 E 1 See-Saw AX 3 E 2 T-Shaped AX 2 E 3 Linear 5 Pairs

34. CHE 106 No. 34 : : : VSEPR and AXE A = central atom; X = number of bond pairs of electrons; E = number of “lone” (unshared) pairs of electrons Angles = 120° and 90° : : : AXEShapeName AX 5 E 0 Trigonal Bipyramid AX 4 E 1 See-Saw AX 3 E 2 T-Shaped AX 2 E 3 Linear 5 Pairs

35. CHE 106 No. 35 VSEPR and AXE A = central atom; X = number of bond pairs of electrons; E = number of “lone” (unshared) pairs of electrons Angles = 180° and 90° : : : : : : AXEShapeName AX 6 E 0 Octahedron AX 5 E 1 Square Pyramid AX 4 E 2 Square Planar AX 3 E 3 T-Shaped 6 Pairs

36. CHE 106 No. 36 VSEPR and AXE A = central atom; X = number of bond pairs of electrons; E = number of “lone” (unshared) pairs of electrons Angles = 180° and 90° : : : : : : AXEShapeName AX 6 E 0 Octahedron AX 5 E 1 Square Pyramid AX 4 E 2 Square Planar AX 3 E 3 T-Shaped 6 Pairs

37. CHE 106 No. 37 VSEPR and AXE A = central atom; X = number of bond pairs of electrons; E = number of “lone” (unshared) pairs of electrons Angles = 180° and 90° : : : : : : AXEShapeName AX 6 E 0 Octahedron AX 5 E 1 Square Pyramid AX 4 E 2 Square Planar AX 3 E 3 T-Shaped 6 Pairs

38. CHE 106 No. 38 VSEPR and AXE A = central atom; X = number of bond pairs of electrons; E = number of “lone” (unshared) pairs of electrons Angles = 180° and 90° : : ::: : AXEShapeName AX 6 E 0 Octahedron AX 5 E 1 Square Pyramid AX 4 E 2 Square Planar AX 3 E 3 T-Shaped 6 Pairs

39. CHE 106 No. 39 VSEPR; BF 4 -2 vs. XeF 4 Lewis Structure bond and lone prs AXE det. parent subst. lone prs det. distortions name struct. BeF 4 -2 Lewis Structure: Be1 x 2= 2 F 4 x 7 = 28 charge= 2 TOTAL= 32 (16 prs) __ |F | Be | F| |F | __ __ __ __ __ __ __ AX 4 E 0 Parent Molecule Be F F F F Tetrahedron

40. CHE 106 No. 40 :: VSEPR Lewis Structure bond and lone prs AXE det. parent subst. lone prs det. distortions name struct. XeF 4 Lewis Structure: Xe1 x 8= 8 F 4 x 7 = 28 TOTAL= 36 (18 prs) __ |F | Xe | F| |F| |F| __ __ __ __ __ AX 4 E 2 Parent Molecule Xe F F F F __ __ __ __ Square Planar

41. CHE 106 No. 41 VSEPR Lewis Structure bond and lone prs AXE det. parent subst. lone prs det. distortions name struct. I 3 -1 Lewis Structure: I 3 x 7= 21 charge= 1 TOTAL= 22 (11 prs) __ | I | I | I| __ __ __ __ AX 2 E 3 Parent Molecule Xe I I __ __ Linear : : : I

42. CHE 106 No. 42 VSEPR Lewis Structure bond and lone prs AXE det. parent subst. lone prs det. distortions name struct. SeF 4 Lewis Structure: Se 1 x 6= 6 F 4 x 7= 28 TOTAL= 34 (17 prs) AX 4 E 1 Parent Molecule Xe F F See-Saw : Se __ |F | Se | F| |F| |F| __ __ __ __ __ __ __ __ F F

43. CHE 106 No. 43 VSEPR “Hints” l For multiple bonds, count only one bonding pair of electrons regardless of the bond order for determining the AXE notation. X - AX = AX  A AX 1 AX 1 AX 1 l For transition metals, disregard d electrons for valence counting and AXE Notation. l Learn only the six parent “shapes” and figure out others from these.

44. CHE 106 No. 44 VSEPR Practice l Try these using VSEPR: » OF 2 » ClO 2 -1 » BF 3 » PBr 3 » TeCl 4 » BrO 4 -1 » SnCl 4 » SF 6 » XeOF 4

45. CHE 106 No. 45 Polarity of Molecules HFHFHFHF  EN = 4.0 - 2.1 = 1.9 Polar Covalent Bond   ElementEN F 4.0 O3.5 N 3.0 C2.5 B2.0 Li1.0 P2.1 Cl3.0 Br2.8 Bond Polarity:  EN S S BCl PF PCl PO LiF NF OO non-polar0 polar covalent1.0 polar covalent1.9 polar covalent0.9 polar covalent1.4 ionic3.0 polar covalent1.0 non-polar0.0

46. CHE 106 No. 46 Polarity of Molecules l Molecules can be polar or non-polar. l Polar molecules are called dipoles since they have positive and negative ends. l Dipoles align in electric field gradient and with one another. (-) (+) +- +- +- +- +- +- +- HFHFHFHF

47. CHE 106 No. 47 Polarity of Molecules Degree of molecular polarity is given by the DIPOLE MOMENT (  given in Debyes; 1 D = 3.3 x 10 -30 coulomb meters) of the molecule.  = Q r(Q = charges and r = separation) Degree of molecular polarity is given by the DIPOLE MOMENT (  given in Debyes; 1 D = 3.3 x 10 -30 coulomb meters) of the molecule.  = Q r(Q = charges and r = separation) l Determining Molecular Dipole Moments (polarity); – requires polar bonds – depends upon the geometry

48. CHE 106 No. 48 Polarity and Geometry C O O Linear (AX 2 E 0 ) Dipole moment = 0 O H H Bent (AX 2 E 2 ) Dipole mom. = 1.84 D

49. CHE 106 No. 49 B F F Trig. Planar (AX 3 E 0 )  = 0 Polarity and Geometry F N F F F Trig. Pyramid (AX 3 E 1 )  = 1.0..

50. CHE 106 No. 50 Covalent Bonding l Closer look at quantum mechanics of covalent bonding. l Orbital Overlap l Wave functions = orbitals

51. CHE 106 No. 51 Orbital Overlap Wave function (wave properties)Wave function (wave properties) Can “constructively” and “destructively add waves (just like ripples on a pond).Can “constructively” and “destructively add waves (just like ripples on a pond). 1s orbital  2 0 radius 1s orbitals  2 0 radius H atom 1 2 Move together to overlap waves

52. CHE 106 No. 52 Covalent Bonding 0 0 radius 2222 H atom 1 2 0 0 radius 2222 H atom 1 2 Destructive Addition of Waves (out of phase) Constructive Addition of Waves (in phase)

53. CHE 106 No. 53 Covalent Bonding + + s orbital - in-phase addition (bonding) s orbital - out-of-phase addition (antibonding)

54. CHE 106 No. 54 Orbital Overlap 0 Energy Distance between atoms

55. CHE 106 No. 55 Hybrid Orbitals l Orbital overlap can become complicated for polyatomic molecules. l Simpler conceptual model developed - Hybridization (valence bond theory). l For central atoms, how can sufficient orbitals be available for electron sharing if they are already occupied in the ground state? – Use conceptual process of electron promotion and forming hybrid orbitals. 2s 2p CaF 2 2s 2p

56. CHE 106 No. 56 Hybridization 2s 2p CaF 2 2s 2p sp hybrids 2p Energy Promotion Hybridization

57. CHE 106 No. 57 sp Hybrid Orbitals l sp hybrid orbitals formed from the combination of one s and one p orbital (linear arrangement). + + linear

58. CHE 106 No. 58 Hybridization 2s 2p BF 3 2s 2p sp 2 hybrids 2p Energy Promotion Hybridization

59. CHE 106 No. 59 sp 2 Hybridization 2s 2p 2s 2p sp 2 hybrids 2p Energy Promotion Hybridization “Unused”’ p atomic orbital on carbon 3 equivalent sp 2 hybrid orbitals

60. CHE 106 No. 60 sp 2 Hybrid Orbitals l sp 2 hybrid orbitals formed from the combination of one s and one p orbital (linear arrangement). + + + trigonal planar

61. CHE 106 No. 61 sp 3 Hybridization 2s 2p CF 4 2s 2p sp 3 hybrids Energy Promotion Hybridization

62. CHE 106 No. 62 sp 3 Hybrid Orbitals l sp 2 hybrid orbitals formed from the combination of one s and one p orbital (linear arrangement). + + + + tetrahedral

63. CHE 106 No. 63 sp 3 d Hybridization Energy Promotion Hybridization sp 3 d hybrids sp d s p d d

64. CHE 106 No. 64 sp 3 d 2 Hybridization Energy Promotion Hybridization sp 3 d 2 hybrids sp d s p d d

65. CHE 106 No. 65 Hybrid Orbitals l Hybridization: – Draw Lewis Structure – Determine VSEPR (AXE) model geometry – Specify hybrid orbitals needed to accommodate the electron pairs to fit the geometry from VSEPR – Shapes : » sp = linearsp 2 = trigonal planar » sp 3 = tetrahedralsp 3 d= trig. bipyramid » sp 3 d 2 = octahedron

66. CHE 106 No. 66 Hybrid Orbitals sp 3 sp 3 d 2 sp 3 d sp = linear sp 2 = trigonal planar

67. CHE 106 No. 67 Hybrid Orbitals and Molecules l Overlap hybrid orbitals to make bonds F F F B F F F B

68. CHE 106 No. 68 Multiple Bonds l Bond Types – Electron density along internuclear axis - SIGMA BOND (  ). – Electron density above and below internuclear axis - PI BOND (  ). 1  (sigma) 0  (pi) 1  (sigma) 1  (pi) 1  (sigma) 2  (pi)

69. CHE 106 No. 69 Double Bonds l Construct sigma bond framework as required then use free p orbitals to construct pi bonds (or lone pairs). Sigma Bonds (sp 2 on C) Pi bonds (p orbs on C) C C H H H H 

70. CHE 106 No. 70 Triple Bonds l Triple bond consists of: – one sigma bond (carbon sp orbitals) – two pi bonds (constructed from the two unused p orbitals on carbon) – NOTE: a pi bond has TWO OVERLAPS Acetylene, C 2 H 4 

71. CHE 106 No. 71 Multiple Bonds Benzene, C 6 H 6 (1) sigma bonds (6C-C and 6C-H) (6C-C and 6C-H) (2) pi bonds 3 C-C de- 3 C-C de- localized localized throughout ring throughout ring l Electrons are delocalized in pi bonds. l Multiple pi bonded systems (such as benzene) allow free movement of electrons within the pi system.

72. CHE 106 No. 72 Benzene l Electrons delocalized throughout pi system (3) of the entire ring. l Lewis structures (resonance forms).

73. CHE 106 No. 73 Benzene

74. CHE 106 No. 74 Hybrid Orbitals Summary l Every bonded pair of atoms shares at least one electron pair. – every bond has one sigma bond localizing electrons between the atoms bonded. – close relationship between hybrid orbitals and molecular geometry l sigma bonds contribute only to the bonding of two atoms l Multiple bonding possible with addition of pi orbitals which may allow long range electron delocalization. (every pi bond has 2 overlaps).

75. CHE 106 No. 75 Molecular Orbitals l Some aspects of bonding are better explained by another model – electrons can be explained using certain wave functions – incorporating these wave functions into predicting aspects of bonding creates this new theory l Main difference - the MO are associated with the entire molecule, not just with the central atom as AXE notation

76. CHE 106 No. 76 Molecular Orbitals Hydrogen Orbitals

77. CHE 106 No. 77 Molecular Orbitals  *(2s)  (2s)  *(1s)  (1s) 2s 2s 1s 1s ENERGY

78. CHE 106 No. 78 Molecular Orbitals Hydrogen Orbitals

79. CHE 106 No. 79 Molecular Orbitals l Bond Order = (No. of Bonding e-) - (No. of *e-) 2 [single bond = 1.0, double bond = 2.0, etc...] [single bond = 1.0, double bond = 2.0, etc...] l Diamagnetic - contains NO unpaired electrons (weakly repelled by magnetic fields) l Paramagnetic - contains at least one unpaired electron (strongly attracted INTO magnetic fields) l Bonding orbitals from the p orbitals switch energies for smallest molecules.

80. CHE 106 No. 80 Hydrogen Molecule  *(2s)  (2s)  *(1s)  (1s) 2s 2s 1s 1s ENERGY HAHAHAHA HBHBHBHB H2H2H2H2 Bond Order = 1.0

81. CHE 106 No. 81 Helium Molecule  *(2s)  (2s)  *(1s)  (1s) 2s 2s 1s 1s ENERGY He A He B He 2 Bond Order = 0.0

82. CHE 106 No. 82 Helium Ion (He 2 +1 )  *(2s)  (2s)  *(1s)  (1s) 2s 2s 1s 1s He A He + B He 2 Bond Order = 0.5 Unpaired Electrons PARAMAGNETIC When making an + ion, always remove the highest energy electrons

83. CHE 106 No. 83 Li 2 Molecule  *(2s)  (2s)  *(1s)  (1s) 2s 2s 1s 1s ENERGY Li A Li B Li 2 Bond Order = 1.0

84. CHE 106 No. 84 Molecular Orbitals from p Orbitals  *(2p x,y ) (antibonding)  b (2p x,y ) (bonding) + +  p (x,y)

85. CHE 106 No. 85 Molecular Orbitals  *(2p z )  *(2s) 2s 2s ENERGY  (2p z ) 2p 2p  (2p x,y )  (2p x,y )  (2s)

86. CHE 106 No. 86 Molecular Orbitals  *(2p z )  (2p z ) 2p 2p  (2p x,y )  (2p x,y )  *(2p z ) 2p 2p  (2p x,y )  (2p x,y ) O thru Ne Li thru N Bonding orbitals from the p’s switch energies for the smallest molecules due to 2s-2p interactions  (2p z )

87. CHE 106 No. 87 NANANANA NBNBNBNB N2N2N2N2 Molecular Orbitals for N 2 b.o. = 8-2 = 3 2  *(2p z )  *(2s) 2s 2s ENERGY  (2p z ) 2p 2p  (2p x,y )  (2p x,y ) DIAMAGNETIC  (2s)

88. CHE 106 No. 88 OAOAOAOA OBOBOBOB O2O2O2O2 Molecular Orbitals for O 2 b.o. = 8-4 = 2 2  *(2p z )  *(2s) 2s 2s ENERGY  (2p z ) 2p 2p  (2p x,y )  (2p x,y )  (2s)

89. CHE 106 No. 89 OAOAOAOA OBOBOBOB O2O2O2O2 Molecular Orbitals for O 2  *(2p z )  (2s) 2s 2s  (2p z ) 2p 2p  (2p x,y )  (2p x,y ) Unpaired Electrons PARAMAGNETIC  *(2s)

90. CHE 106 No. 90 Molecular Orbitals for Period 2 p sublevel  *(2p z )  *(2s)  (2p z )  (2p x,y )  (2p x,y )  (2s) B 2 C 2 N 2 N 2 +1 bond order 1.0 2.0 3.0 2.5

91. CHE 106 No. 91 Molecular Orbitals for Period 2 p sublevel  *(2p z )  *(2s)  (2p z )  (2p x,y )  (2p x,y )  (2s) O 2 F 2 Ne 2 F 2 +1 bond order 2.0 1.0 0.0 1.5

92. CHE 106 No. 92 Chapter Nine l Molecular Geometry – VSEPR AND AXE theories – Predicting shapes from Lewis structures. – octet rules and exceptions – distortions l Molecular Polarity l Valence Bond theory (hybridization) – sigma and pi bonding – molecular shapes – electron delocalization

93. CHE 106 No. 93 Chapter Nine l Molecular Orbital theory – bonding vs. antibonding electrons – bond order – diamagnetic and paramagnetic