1 © 2006 Brooks/Cole - Thomson Chemistry and Chemical Reactivity 6th Edition John C. Kotz Paul M. Treichel Gabriela C. Weaver CHAPTER 10 Bonding and Molecular Structure: Orbital Hybridization and Molecular Orbitals © 2006 Brooks/Cole Thomson Lectures written by John Kotz

2 © 2006 Brooks/Cole - Thomson Advanced Theories of Chemical Bonding Chapter 10 Atomic Orbitals Molecules

3 © 2006 Brooks/Cole - Thomson MOLECULAR ORBITAL THEORY — Robert Mullikan ( )MOLECULAR ORBITAL THEORY — Robert Mullikan ( ) valence electrons are delocalizedvalence electrons are delocalized valence electrons are in orbitals (called molecular orbitals) spread over entire molecule.valence electrons are in orbitals (called molecular orbitals) spread over entire molecule. Two Theories of Bonding

4 © 2006 Brooks/Cole - Thomson Two Theories of Bonding VALENCE BOND THEORY — Linus PaulingVALENCE BOND THEORY — Linus Pauling valence electrons are localized between atoms (or are lone pairs).valence electrons are localized between atoms (or are lone pairs). half-filled atomic orbitals overlap to form bonds.half-filled atomic orbitals overlap to form bonds. See Screen 10.3 and Figures 10.1 and 10.2.See Screen 10.3 and Figures 10.1 and 10.2.

5 © 2006 Brooks/Cole - Thomson Sigma Bond Formation by Orbital Overlap Two s orbitals overlap

6 © 2006 Brooks/Cole - Thomson Sigma Bond Formation Two s orbitals overlap Two p orbitals overlap

7 © 2006 Brooks/Cole - Thomson Using VB Theory Bonding in BF 3 planar triangle angle = 120 o

8 © 2006 Brooks/Cole - Thomson Bonding in BF 3 How to account for 3 bonds 120 o apart using a spherical s orbital and p orbitals that are 90 o apart?How to account for 3 bonds 120 o apart using a spherical s orbital and p orbitals that are 90 o apart? Pauling said to modify VB approach with ORBITAL HYBRIDIZATIONPauling said to modify VB approach with ORBITAL HYBRIDIZATION — mix available orbitals to form a new set of orbitals — HYBRID ORBITALS — that will give the maximum overlap in the correct geometry. (See Screen 10.6)— mix available orbitals to form a new set of orbitals — HYBRID ORBITALS — that will give the maximum overlap in the correct geometry. (See Screen 10.6)

9 © 2006 Brooks/Cole - Thomson Bonding in BF 3 See Figure 10.9 and Screen 10.6 rearrange electronshydridize orbs. unused p orbital three sp 2 hybrid orbitals 2p 2s

10 © 2006 Brooks/Cole - Thomson The three hybrid orbitals are made from 1 s orbital and 2 p orbitals  3 sp 2 hybrids. The three hybrid orbitals are made from 1 s orbital and 2 p orbitals  3 sp 2 hybrids. Bonding in BF 3 Now we have 3, half-filled HYBRID orbitals that can be used to form B-F sigma bonds.Now we have 3, half-filled HYBRID orbitals that can be used to form B-F sigma bonds.

11 © 2006 Brooks/Cole - Thomson An orbital from each F overlaps one of the sp 2 hybrids to form a B-F  bond. Bonding in BF 3

12 © 2006 Brooks/Cole - Thomson BF 3, Planar Trigonal

13 © 2006 Brooks/Cole - Thomson Bonding in CH 4 How do we account for 4 C—H sigma bonds 109 o apart? Need to use 4 atomic orbitals — s, p x, p y, and p z — to form 4 new hybrid orbitals pointing in the correct direction.

14 © 2006 Brooks/Cole - Thomson 4 C atom orbitals hybridize to form four equivalent sp 3 hybrid atomic orbitals. Bonding in a Tetrahedron — Formation of Hybrid Atomic Orbitals

15 © 2006 Brooks/Cole - Thomson Bonding in a Tetrahedron — Formation of Hybrid Atomic Orbitals 4 C atom orbitals hybridize to form four equivalent sp 3 hybrid atomic orbitals.

16 © 2006 Brooks/Cole - Thomson Bonding in CH 4, Figure 10.6 Figure 10.6

17 © 2006 Brooks/Cole - Thomson

18 Bonding in Glycine

19 © 2006 Brooks/Cole - Thomson Bonding in Glycine

20 © 2006 Brooks/Cole - Thomson Bonding in Glycine

21 © 2006 Brooks/Cole - Thomson Bonding in Glycine

22 © 2006 Brooks/Cole - Thomson Bonding in Glycine

23 © 2006 Brooks/Cole - Thomson

24 Orbital Hybridization Figure 10.5 BONDSSHAPEHYBRID REMAIN 2linear sp2 p’s 3trigonal sp 2 1 p planar 4tetrahedral sp 3 none

25 © 2006 Brooks/Cole - Thomson Multiple Bonds Consider ethylene, C 2 H 4

26 © 2006 Brooks/Cole - Thomson Sigma Bonds in C 2 H 4

27 © 2006 Brooks/Cole - Thomson π Bonding in C 2 H 4 The unused p orbital on each C atom contains an electron and this p orbital overlaps the p orbital on the neighboring atom to form the π bond. (See Fig. 10.8)

28 © 2006 Brooks/Cole - Thomson π Bonding in C 2 H 4 The unused p orbital on each C atom contains an electron and this p orbital overlaps the p orbital on the neighboring atom to form the π bond. (See Fig )

29 © 2006 Brooks/Cole - Thomson Multiple Bonding in C 2 H 4

30 © 2006 Brooks/Cole - Thomson  and π Bonding in C 2 H 4 Figure 10.10

31 © 2006 Brooks/Cole - Thomson  and π Bonding in CH 2 O Figure 10.11

32 © 2006 Brooks/Cole - Thomson  and π Bonding in C 2 H 2 Figure 10.12

33 © 2006 Brooks/Cole - Thomson  and π Bonding in C 2 H 2 Figure 10.12

34 © 2006 Brooks/Cole - Thomson Consequences of Multiple Bonding Figure There is restricted rotation around C=C bond.

35 © 2006 Brooks/Cole - Thomson Consequences of Multiple Bonding Restricted rotation around C=C bond.

36 © 2006 Brooks/Cole - Thomson Double Bonds and Vision See Screen 10.13, Molecular Orbitals and Vision