This chapter discusses additional aspects of chemical bonding theory including the valence bond method, hybridization of atomic orbitals, multiple bonds, and molecular orbital theory. It also covers delocalized bonding in molecules like benzene and bonding in metals. The chapter examines topics like photoelectron spectroscopy and presents example problems at the end.

1. Philip Dutton
University of Windsor, Canada
N9B 3P4
Prentice-Hall © 2002
General Chemistry
Principles and Modern Applications
Petrucci • Harwood • Herring
8th
Edition
Chapter 12: Chemical Bonding II:
Additional Aspects

2. Prentice-Hall General Chemistry: Chapter 12Slide 2 of 47
Contents
12-1 What a Bonding Theory Should Do
12-2 Introduction to the Valence-Bond Method
12-3 Hybridization of Atomic Orbitals
12-4 Multiple Covalent Bonds
12-5 Molecular Orbital Theory
12-6 Delocalized Electrons: Bonding in the
Benzene Molecule
12-7 Bonding in Metals
Focus on Photoelectron Spectroscopy

3. Prentice-Hall General Chemistry: Chapter 12Slide 3 of 47
12-1 What a Bonding Theory Should Do
• Bring atoms together from a distance.
– e-
are attracted to both nuclei.
– e-
are repelled by each other.
– Nuclei are repelled by each other.
• Plot the total potential energy verses distance.
– -ve energies correspond to net attractive forces.
– +ve energies correspond to net repulsive forces.

4. Prentice-Hall General Chemistry: Chapter 12Slide 4 of 47
Potential Energy Diagram

5. Prentice-Hall General Chemistry: Chapter 12Slide 5 of 47
12-2 Introduction to the Valence-Bond
Method
• Atomic orbital overlap describes covalent
bonding.
• Area of overlap of orbitals is in phase.
• A localized model of bonding.

6. Prentice-Hall General Chemistry: Chapter 12Slide 6 of 47
Bonding in H2S

7. Prentice-Hall General Chemistry: Chapter 12Slide 7 of 47
Example 12-1
Using the Valence-Bond Method to Describe a Molecular
Structure.
Describe the phosphine molecule, PH3, by the valence-bond
method..
Identify valence electrons:

8. Prentice-Hall General Chemistry: Chapter 12Slide 8 of 47
Example 12-1
Sketch the orbitals:
Overlap the orbitals:
Describe the shape: Trigonal pyramidal

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12-3 Hybridization of Atomic Orbitals

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sp3
Hybridization

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sp3
Hybridization

12. Prentice-Hall General Chemistry: Chapter 12Slide 12 of 47
Bonding in Methane

13. Prentice-Hall General Chemistry: Chapter 12Slide 13 of 47
sp3
Hybridization in Nitrogen

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Bonding in Nitrogen

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sp2
Hybridization

16. Prentice-Hall General Chemistry: Chapter 12Slide 16 of 47
Orbitals in Boron

17. Prentice-Hall General Chemistry: Chapter 12Slide 17 of 47
sp Hybridization

18. Prentice-Hall General Chemistry: Chapter 12Slide 18 of 47
Orbitals in Beryllium

19. Prentice-Hall General Chemistry: Chapter 12Slide 19 of 47
sp3
d and sp3
d2
Hybridization

20. Prentice-Hall General Chemistry: Chapter 12Slide 20 of 47
Hybrid Orbitals and VSEPR
• Write a plausible Lewis structure.
• Use VSEPR to predict electron geometry.
• Select the appropriate hybridization.

21. Prentice-Hall General Chemistry: Chapter 12Slide 21 of 47
12-4 Multiple Covalent Bonds
• Ethylene has a double bond in its Lewis structure.
• VSEPR says trigonal planar at carbon.

22. Prentice-Hall General Chemistry: Chapter 12Slide 22 of 47
Ethylene

23. Prentice-Hall General Chemistry: Chapter 12Slide 23 of 47
Acetylene
• Acetylene, C2H2, has a triple bond.
• VSEPR says linear at carbon.

24. Prentice-Hall General Chemistry: Chapter 12Slide 24 of 47
12-5 Molecular Orbital Theory
• Atomic orbitals are isolated on atoms.
• Molecular orbitals span two or more atoms.
• LCAO
– Linear combination of atomic orbitals.
Ψ1 = φ1 + φ2 Ψ2 = φ1 - φ2

25. Prentice-Hall General Chemistry: Chapter 12Slide 25 of 47
Combining Atomic Orbitals

26. Prentice-Hall General Chemistry: Chapter 12Slide 26 of 47
Molecular Orbitals of Hydrogen

27. Prentice-Hall General Chemistry: Chapter 12Slide 27 of 47
Basic Ideas Concerning MOs
• Number of MOs = Number of AOs.
• Bonding and antibonding MOs formed from AOs.
• e-
fill the lowest energy MO first.
• Pauli exclusion principle is followed.
• Hund’s rule is followed

28. Prentice-Hall General Chemistry: Chapter 12Slide 28 of 47
Bond Order
• Stable species have more electrons in bonding
orbitals than antibonding.
Bond Order =
No. e-
in bonding MOs - No. e- in antibonding MOs
2

29. Prentice-Hall General Chemistry: Chapter 12Slide 29 of 47
Diatomic Molecules of the First-Period
BO = (1-0)/2 = ½H2
+
BO = (2-0)/2 = 1H2
+
BO = (2-1)/2 = ½He2
+
BO = (2-2)/2 = 0He2
+
BO = (e-
bond - e-
antibond )/2

30. Prentice-Hall General Chemistry: Chapter 12Slide 30 of 47
Molecular Orbitals of the Second Period
• First period use only 1s orbitals.
• Second period have 2s and 2p orbitals available.
• p orbital overlap:
– End-on overlap is best – sigma bond (σ).
– Side-on overlap is good – pi bond (π).

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Molecular Orbitals of the Second Period

32. Prentice-Hall General Chemistry: Chapter 12Slide 32 of 47
Combining p orbitals

33. Prentice-Hall General Chemistry: Chapter 12Slide 33 of 47
Expected MO Diagram of C2
Prentice-Hall © 2002 General Chemistry: Chapter 12 Slide

34. Prentice-Hall General Chemistry: Chapter 12Slide 34 of 47
Modified MO Diagram of C2

35. Prentice-Hall General Chemistry: Chapter 12Slide 35 of 47Prentice-Hall © 2002 General Chemistry: Chapter 12
MO Diagrams of 2nd
Period Diatomics

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MO Diagrams of Heteronuclear Diatomics

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12-6 Delocalized Electrons

38. Prentice-Hall General Chemistry: Chapter 12Slide 38 of 47
Benzene

39. Prentice-Hall General Chemistry: Chapter 12Slide 39 of 47
Benzene

40. Prentice-Hall General Chemistry: Chapter 12Slide 40 of 47
Ozone

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12-7 Bonding in Metals
• Electron sea model
– Nuclei in a sea of e-
.
– Metallic lustre.
– Malleability.
Force applied

42. Prentice-Hall General Chemistry: Chapter 12Slide 42 of 47
Bonding in Metals
Band theory.
• Extension of MO theory.
N atoms give N orbitals that
are closely spaced in energy.
• N/2 are filled.
The valence band.
• N/2 are empty.
The conduction band.

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Band Theory

44. Prentice-Hall General Chemistry: Chapter 12Slide 44 of 47
Semiconductors

45. Prentice-Hall General Chemistry: Chapter 12Slide 45 of 47
Photovoltaic Cells

46. Prentice-Hall General Chemistry: Chapter 12Slide 46 of 47
Focus on Photoelectron Spectroscopy

47. Prentice-Hall General Chemistry: Chapter 12Slide 47 of 47
Chapter 12 Questions
1, 3, 8, 10, 16, 29, 33,
39, 45, 59, 68, 72, 76