General Chemistry Principles and Modern Applications Petrucci Harwood Herring 8 th Edition Chapter 12: Chemical Bonding II: Additional Aspects Philip Dutton University of Windsor, Canada N9B 3P4 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 Prentice-Hall 2002 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 2 of 47 12-1 What a Bonding Theory Should Do Potential Energy Diagram 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. Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 3 of 47 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 4 of 47 12-2 Introduction to the Valence-Bond Method Bonding in H 2 S Atomic orbital overlap describes covalent bonding. Area of overlap of orbitals is in phase. A localized model of bonding. Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 5 of 47 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 6 of 47
Example 12-1 Using the Valence-Bond Method to Describe a Molecular Structure. Describe the phosphine molecule, PH 3, by the valence-bond method.. Identify valence electrons: Example 12-1 Sketch the orbitals: Overlap the orbitals: Describe the shape: Trigonal pyramidal Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 7 of 47 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 8 of 47 12-3 Hybridization of Atomic Orbitals sp 3 Hybridization Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 9 of 47 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 10 of 47 sp 3 Hybridization Bonding in Methane Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 11 of 47 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 12 of 47
sp 3 Hybridization in Nitrogen Bonding in Nitrogen Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 13 of 47 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 14 of 47 sp 2 Hybridization Orbitals in Boron Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 15 of 47 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 16 of 47 sp Hybridization Orbitals in Beryllium Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 17 of 47 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 18 of 47
sp 3 d and sp 3 d 2 Hybridization Hybrid Orbitals and VSEPR Write a plausible Lewis structure. Use VSEPR to predict electron geometry. Select the appropriate hybridization. Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 19 of 47 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 20 of 47 12-4 Multiple Covalent Bonds Ethylene Ethylene has a double bond in its Lewis structure. VSEPR says trigonal planar at carbon. Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 21 of 47 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 22 of 47 Acetylene 12-5 Molecular Orbital Theory Acetylene, C 2 H 2, has a triple bond. VSEPR says linear at carbon. Atomic orbitals are isolated on atoms. Molecular orbitals span two or more atoms. LCAO Linear combination of atomic orbitals. Ψ 1 = φ 1 + φ 2 Ψ 2 = φ 1 - φ 2 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 23 of 47 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 24 of 47
Combining Atomic Orbitals Molecular Orbitals of Hydrogen Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 25 of 47 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 26 of 47 Basic Ideas Concerning MOs Bond Order 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 Stable species have more electrons in bonding orbitals than antibonding. Bond Order = No. e- in bonding MOs - No. e- in antibonding MOs 2 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 27 of 47 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 28 of 47 Diatomic Molecules of the First-Period BO = (e - bond -e- antibond )/2 BO H 2 + = (1-0)/2 = ½ Molecular Orbitals of the Second Period First period use only 1s orbitals. Second period have 2s and 2p orbitals available. BO = (2-0)/2 = 1 H 2 + BO He 2 + = (2-1)/2 = ½ p orbital overlap: End-on overlap is best sigma bond (σ). Side-on overlap is good pi bond (π). BO = (2-2)/2 = 0 He 2 + Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 29 of 47 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 30 of 47
Molecular Orbitals of the Second Period Combining p orbitals Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 31 of 47 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 32 of 47 Expected MO Diagram of C 2 Modified MO Diagram of C 2 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 33 of 47 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 34 of 47 MO Diagrams of 2 nd Period Diatomics MO Diagrams of Heteronuclear Diatomics Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 35 of 47 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 36 of 47
12-6 Delocalized Electrons Benzene Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 37 of 47 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 38 of 47 Benzene Ozone Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 39 of 47 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 40 of 47 12-7 Bonding in Metals Electron sea model Nuclei in a sea of e -. Metallic lustre. Malleability. Force applied 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. Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 41 of 47 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 42 of 47
Band Theory Semiconductors Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 43 of 47 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 44 of 47 Photovoltaic Cells Focus on Photoelectron Spectroscopy Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 45 of 47 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 46 of 47 Chapter 12 Questions 1, 3, 8, 10, 16, 29, 33, 39, 45, 59, 68, 72, 76 Prentice-Hall 2002 General Chemistry: Chapter 12 Slide 47 of 47