Chapter 11: Chemical Bonding II: Additional Aspects Chemistry 140 Fall 2002 CHEMISTRY Ninth Edition GENERAL Principles and Modern Applications Petrucci • Harwood • Herring • Madura Chapter 11: Chemical Bonding II: Additional Aspects Philip Dutton University of Windsor, Canada Prentice-Hall © 2007 General Chemistry: Chapter 11 Prentice-Hall © 2007
Contents 11-1 What a Bonding Theory Should Do Chemistry 140 Fall 2002 Contents 11-1 What a Bonding Theory Should Do 11-2 Introduction to the Valence-Bond Method 11-3 Hybridization of Atomic Orbitals 11-4 Multiple Covalent Bonds 11-5 Molecular Orbital Theory 11-6 Delocalized Electrons: Bonding in the Benzene Molecule 11-7 Bonding in Metals 11-8 Some Unresolved Issues: Can Electron Charge-Density Plots Help? Focus On Photoelectron Spectroscopy General Chemistry: Chapter 11 Prentice-Hall © 2007
11-1 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. General Chemistry: Chapter 11 Prentice-Hall © 2007
Potential Energy Diagram General Chemistry: Chapter 11 Prentice-Hall © 2007
11-2 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. General Chemistry: Chapter 11 Prentice-Hall © 2007
General Chemistry: Chapter 11 Chemistry 140 Fall 2002 Bonding in H2S General Chemistry: Chapter 11 Prentice-Hall © 2007
General Chemistry: Chapter 11 EXAMPLE 11-1 Using the Valence-Bond Method to Describe a Molecular Structure. Describe the phosphine molecule, PH3, by the valence-bond method.. Identify valence electrons: General Chemistry: Chapter 11 Prentice-Hall © 2007
General Chemistry: Chapter 11 Chemistry 140 Fall 2002 EXAMPLE 11-1 Sketch the orbitals: H Overlap the orbitals: H H H Describe the shape: Trigonal pyramidal General Chemistry: Chapter 11 Prentice-Hall © 2007
11-3 Hybridization of Atomic Orbitals General Chemistry: Chapter 11 Prentice-Hall © 2007
General Chemistry: Chapter 11 sp3 Hybridization General Chemistry: Chapter 11 Prentice-Hall © 2007
General Chemistry: Chapter 11 sp3 Hybridization General Chemistry: Chapter 11 Prentice-Hall © 2007
General Chemistry: Chapter 11 Bonding in Methane General Chemistry: Chapter 11 Prentice-Hall © 2007
sp3 Hybridization in Nitrogen General Chemistry: Chapter 11 Prentice-Hall © 2007
General Chemistry: Chapter 11 Bonding in Nitrogen General Chemistry: Chapter 11 Prentice-Hall © 2007
General Chemistry: Chapter 11 sp2 Hybridization General Chemistry: Chapter 11 Prentice-Hall © 2007
General Chemistry: Chapter 11 Orbitals in Boron General Chemistry: Chapter 11 Prentice-Hall © 2007
General Chemistry: Chapter 11 sp Hybridization General Chemistry: Chapter 11 Prentice-Hall © 2007
General Chemistry: Chapter 11 Orbitals in Beryllium General Chemistry: Chapter 11 Prentice-Hall © 2007
sp3d and sp3d2 Hybridization General Chemistry: Chapter 11 Prentice-Hall © 2007
Hybrid Orbitals and VSEPR Write a plausible Lewis structure. Use VSEPR to predict electron geometry. Select the appropriate hybridization. General Chemistry: Chapter 11 Prentice-Hall © 2007
11-4 Multiple Covalent Bonds Ethylene has a double bond in its Lewis structure. VSEPR says trigonal planar at carbon. General Chemistry: Chapter 11 Prentice-Hall © 2007
General Chemistry: Chapter 11 Ethylene General Chemistry: Chapter 11 Prentice-Hall © 2007
General Chemistry: Chapter 11 Acetylene Acetylene, C2H2, has a triple bond. VSEPR says linear at carbon. General Chemistry: Chapter 11 Prentice-Hall © 2007
11-5 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 General Chemistry: Chapter 11 Prentice-Hall © 2007
Combining Atomic Orbitals Chemistry 140 Fall 2002 Combining Atomic Orbitals General Chemistry: Chapter 11 Prentice-Hall © 2007
Molecular Orbitals of Hydrogen General Chemistry: Chapter 11 Prentice-Hall © 2007
Basic Ideas Concerning MOs Chemistry 140 Fall 2002 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 General Chemistry: Chapter 11 Prentice-Hall © 2007
General Chemistry: Chapter 11 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 General Chemistry: Chapter 11 Prentice-Hall © 2007
Diatomic Molecules of the First-Period BO = (e-bond - e-antibond )/2 BO = (1-0)/2 = ½ H2+ BO = (2-0)/2 = 1 H2 BO = (2-1)/2 = ½ He2+ BO = (2-2)/2 = 0 He2 General Chemistry: Chapter 11 Prentice-Hall © 2007
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). General Chemistry: Chapter 11 Prentice-Hall © 2007
Molecular Orbitals of the Second Period General Chemistry: Chapter 11 Prentice-Hall © 2007
General Chemistry: Chapter 11 Combining p orbitals General Chemistry: Chapter 11 Prentice-Hall © 2007
Expected MO Diagram of C2 Slide 33 of 53 General Chemistry: Chapter 11 Prentice-Hall © 2007 General Chemistry: Chapter 11 Prentice-Hall © 2007
Modified MO Diagram of C2 General Chemistry: Chapter 11 Prentice-Hall © 2007
MO Diagrams of 2nd Period Diatomics Slide 35 of 53 General Chemistry: Chapter 11 Prentice-Hall © 2007 Prentice-Hall © 2002 General Chemistry: Chapter 11 General Chemistry: Chapter 11 Prentice-Hall © 2007
MO Diagrams of Heteronuclear Diatomics General Chemistry: Chapter 11 Prentice-Hall © 2007
11-6 Delocalized Electrons General Chemistry: Chapter 11 Prentice-Hall © 2007
General Chemistry: Chapter 11 Benzene General Chemistry: Chapter 11 Prentice-Hall © 2007
General Chemistry: Chapter 11 Benzene General Chemistry: Chapter 11 Prentice-Hall © 2007
General Chemistry: Chapter 11 Benzene General Chemistry: Chapter 11 Prentice-Hall © 2007
General Chemistry: Chapter 11 Ozone General Chemistry: Chapter 11 Prentice-Hall © 2007
General Chemistry: Chapter 11 11-7 Bonding in Metals Electron sea model Nuclei in a sea of e-. Metallic luster. Malleability. Force applied General Chemistry: Chapter 11 Prentice-Hall © 2007
General Chemistry: Chapter 11 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. General Chemistry: Chapter 11 Prentice-Hall © 2007
General Chemistry: Chapter 11 Band Theory General Chemistry: Chapter 11 Prentice-Hall © 2007
General Chemistry: Chapter 11 Chemistry 140 Fall 2002 Semiconductors General Chemistry: Chapter 11 Prentice-Hall © 2007
General Chemistry: Chapter 11 Photovoltaic Cells General Chemistry: Chapter 11 Prentice-Hall © 2007
11-8 Some Unresolved Issues: Can Electron Charge-Density Plots Help? Accommodation of extra valence electrons? In molecules such as SF6 and SF4. Are d-orbitals used in the bonding description? What provides the more fundamental view of molecular shape? VSEPR? Hybridization? General Chemistry: Chapter 11 Prentice-Hall © 2007
General Chemistry: Chapter 11 Bonding in SF6 ? 0.53- 3.17+ ? General Chemistry: Chapter 11 Prentice-Hall © 2007
Isodensity Contour Map of SCl2 General Chemistry: Chapter 11 Prentice-Hall © 2007
Contour Map of the Electron Density in SCl2 General Chemistry: Chapter 11 Prentice-Hall © 2007
General Chemistry: Chapter 11 Bonding in H2SO4 and SO42- 0.002 au 0.22 au 0.28 au General Chemistry: Chapter 11 Prentice-Hall © 2007
Focus on Photoelectron Spectroscopy General Chemistry: Chapter 11 Prentice-Hall © 2007
End of Chapter Questions Set up a strategy for your problem. This is your road map. In a time of stress (i.e. an exam) your strategy will keep you on the path of the problem. Change your strategy If it is identifiably faulty (remember your units). General Chemistry: Chapter 11 Prentice-Hall © 2007