Chapter 5 Molecular. removed are labeled in brackets as the chapter opener is below. [Chapter opener]

Transcription

1 Chapter 5 Molecular Orbitals Figures and table removed are labeled in brackets as the chapter opener is below [Chapter opener]

2 5.1 Formation of Molecular Orbitals from Atomic Orbitals

3 Molecular Orbitals Linear Combination of Atomic Orbitals LCAO Ψ = c a ψ a + c b ψ b Ψ = molecular orbital ψ a = atomic orbital atom a c a = coefficient of atomic orbital

4 5.1.1 Molecular Orbitals from s Orbitals

5 MOs formed by s orbitals (H 2, He 2, H 2+, etc.) [Figure 5.1]

6 Sigma symmetry MO [Figure page 120 top]

7 Pi symmetry MOs [Figure page 120 bottom]

8 Go to Orbitron for MO movie Orbitron a gallery of orbitals

9 Go to Models 360 for rotatable orbitals Models 360 has molecular orbitals in a java applet

10 5.1.2 Molecular Orbitals from p Orbitals

11 [Figure 5.2]

12 Sigma MOs from p [Figure 5.2(a) ] Copyright 2014 Pearson Education, Inc.

13 Pi MOs from p [Figure 5.2(b)] Copyright 2014 Pearson Education, Inc.

14 Energy level diagram for p molecular orbitals [Figure 5.2 (c)] Copyright 2014 Pearson Education, Inc.

15 Go to Orbitron for MO movie Orbitron a gallery of orbitals

16 Go to Models 360 for rotatable orbitals Models 360 has molecular orbitals in a java applet

17 5.1.3 Molecular Orbitals from d Orbitals

18 Possible d MO interactions [Figure 5.3]

19 5.1.4 Nonbonding Orbitals and Other Factors

20 Energy match and MOs [Figure 5.4]

21 MO interaction forbidden by symmetry [Figure 5.3(b)]

22 5.2 Homonuclear Diatomic Orbitals 2 nd period using 2s and 2p atomis orbitals

23 5.2.1 Molecular Orbitals

24 Diatomics no s-p mixing [Figure 5.5]

25 5.2.2 Orbital Mixing

26 s and p mixing [Figure 5.6]

27 Illustration of s-p mixing

28 5.2.3 Diatomic Orbitals of the First and Second Period

29 No mixing O 2 and F 2 [Figure 5.6(a)]

30 s and p mixing Li 2, Be 2, B 2, C 2, [Figure 5.6(b)] and N 2

31 Bond order For molecular orbitals, bond order is calculated by Bond order = ½ (Bonding electrons Antibonding electrons)

32 Population of orbitals for second row homonuclear diatomcs [Figure 5.7]

33 Bond Distances in carbon and oxygen diatomics [Two tables on page 128]

34 [Figure 5.8] Bond distances

35 Covalent radii = ½ bond length [Figure 5.9]

36 [Table 5.1]

37 5.2.4 Photoelectron Spectroscopy skip

38 5.3 Heteronuclear Diatomic Molecules

39 5.3.1 Polar Bonds

40 [Table 5.2]

41 Relative orbital energies [Figure 5.12]

42 HF [Figure in examnple 5.3 page 137]

43 5.3.2 Inorganic Compounds and Molecular Orbitals

44 [Figure 5.14] LiF

45 CO [Figure 5.13]

46 Go to Models 360 for rotatable orbitals Models 360 has molecular orbitals in a java applet

47 5.4 Molecular Orbitals for Larger Molecules

48 5.4.1 FHF-

49 FHF - Introducing the group orbital approach The formation of FHF - can be thought of as separation of F 2 orbitals and insertion of H - in the center.

50 F2 group orbitals [Figure 5.16]

51 The bonding and antibonding orbitals in FHF - [Figure 5.17]

52 FHF- MO diagram [Figure 5.18]

53 5.4.2 CO 2 the Symmetry Adapted Linear Combination (SALC) approach

54 Steps in the symmetry adapted MO approach Assign point group to molecule. Use a lower symmetry for linear Assign a coordinate system. Highest axis = z. Construct a reducible representation of the s orbitals on the outer atoms. Carry out symmetry operations, and character = 1 if atom moves other wise zero. Repeat for p orbitals on outer atom, and character = 1 if p is same, -1 if the negative, and zero if it moves. Reduce the representation to get the symmetry of the group orbitals. (Construct the group orbitals.) Match group orbitals with orbitals on the central atom of the same symmetry. Construct MO from interaction of orbitals of the same symmetry Construct the MO energy level diagram

55 CO 2 Point group is D h. Infinite axis. Easier to use lower Symmetry sub group D2h. Molecular axis to right is z. x axis straight up. y axis is pointing straight out of page.

56 Outer s orbitals reducible rep. [Table page 144 top] Reduction [Table page 144 bottom]

57 Outer p orbitals reducible rep. Reduction not shown, symmetries on next page [Table page 144 middle]

58 [Figure 5.18] CO 2 group orbitals

59 [Page 145] D 2 h character table

60 Central atom (C) orbital symmetries [Figure 5.18] s =Ag (two group orbitals p x = B 3 u (one) p y = B 2 u (one) p z = B 1 u (two) Note B 2 g and B 3 g has no match on central atom. These MOs are non-bonding

61 Symmetries of the central atom orbitals [Figure 5.19]

62 Energy match of C and O [Figure 5.22]

63 [Figure 5.20] Ag and B 1 u s MOs

64 [Figure 5.21] A g and B 1 u p MOs

65 [Figure 5.23] B 2 u and B 3 g p MOs

66 [Figure 5.24] B 3 u and B 2 g p MOs

67 CO 2 MO energy levels [Figure 5.25]

68 5.4.3 H 2 O

69 [Figure 5.26] H 2 O

70 [Table 5.3]

71 H 2 O [Figure 5.27]

72 Drawings of water molecular orbital formation [Table 5.4]

73 H 2 O MO energy [Figure 5.28] levels

74 5.4.4 NH3

75 NH 3 [Figure 5.29]

76 [Table 5.5]

77 Using the projection method to generate orbitals Project one orbital through every symmetry operation [Table middle of page 153] Multiply the projection by the characters of the orbital symmetries [Table bottom of 153] Copyright 2014 Pearson Education, Inc.

78 The resulting group orbitals [Three figures in the margins of pages 154 and 155]

79 Copyright 2014 Pearson Education, Inc. [Table 5.6]

80 NH 3 MO energy levels [Figure 5.30]

81 skip CO 2 revisited with projection operators

82 5.4.6 BF3

83 Note, I have two separate pdf files on BF 3 that will be on the web page

84 BF 3 orbital generation [Figure 5.31]

85 BF 3 MO energy levels [Figure 5.32]

86 5.4.7 Hybrid orbitals

87 Hybrid orbital procedure for CH 4 [Figure and table from page 162]

88 Hybrid orbitals [Figure 5.34]