Contents. Preface to the Second Edition. Acknowledgments

Transcription

1 Contents Preface to the Second Edition Preface Acknowledgments xi xiii xv 1. How Science Deals with Complex Problems Introduction: Levels in Science What Are Molecules Made of? Interactions Between Atoms The Simplest Examples: H 2 andlih The hydrogen molecule The lithium hydride molecule What about the other Li electrons? What about the nuclear repulsions? Comments on H 2 andlih How to Proceed? Assignment for Chapter Appendix A How to Interpret 3D Contours 19 A.1 Thinking in 3D A.2 The Electron Distribution of the Lithium 2s Electron.. 22 A.2.1 How does this relate to the text-book orbitals. 25 A.2.2 What if the distribution is not spherical? Appendix B Must We Use Quantum Theory? 29 v

2 vi Contents B.1 Connections to Laws of Nature B.2 Stable Molecules B.3 The Equipartition of Energy B.4 Quantum Summary What We Know About Atoms and Molecules Atomic Electronic Structure The hydrogen atom Many-electron atoms The Pauli principle Statement of the Pauli principle Using the Atomic Energy-Level Scheme Current summary for atoms Empirical Chemistry Assignment for Chapter Appendix C The Interpretation of Orbitals 53 C.1 What is an Orbital? C.2 Orbitals: Atomic and Molecular A Strategy for Electronic Structure Review Lithium Hydride Again Polarisation and hybrid AOs Molecular orbitals Quick summary Assignment for Chapter Appendix D Is Hybridisation a Real Process? The Pauli Principle and Orbitals A Difficulty with Helium When are Orbitals Mutually Exclusive? Does this Work for AOs? The Helium Molecule Again The Rôle of Atomic Orbitals in Valence Theory Current Summary for LiH and He Assignment for Chapter A Model Polyatomic: Methane 89

3 Contents vii 5.1 The Methane Molecule: CH The Electronic Structure of Methane The Shape of the Methane Molecule What About the Pauli principle? Preliminary summary for methane The Chemist s Description of Methane How to use these structures: the valence bond method Summary for Methane Assignment for Chapter Appendix E Valence as Electron Spin Pairing Lone Pairs of Electrons Why are Not All Electrons Involved in Bonding What is a Lone Pair? The ammonia molecule The water molecule The Shapes of Simple Molecules The water molecule again Reactions of Lone Pairs A Working Summary Assignment for Chapter Organic Molecules with Multiple Bonds Double and Triple Bonds The Possibilities Ethene and Methanal The Double Bond in Ethene and Methanal Sigma (σ) and Pi (π) notation in planar molecules The σ and π Orbitals in C 2 H 4 and CH 2 O Ethene contours Methanal contours Relative energies of the two bonds Reactivity of a Double Bond Multiple Bonds in General Assignment for Chapter Molecular Symmetry 143

4 viii Contents 8.1 The Question of Symmetry Symmetry: Generalisation Case Studies: H 2 O and Benzene The H 2 O molecule The benzene σ system Bond MOs and Symmetry MOs A Cautionary Note Assignment for Chapter Appendix F Buridan s Ass and Molecular Symmetry Diatomics with Multiple Bonds Motivation The Nitrogen Molecule: N Energies of the N 2 MOs Symmetry and the N 2 molecule The Carbon Monoxide Molecule: CO Other Homonuclear Diatomics The oxygen molecule: O Lessons from Diatomics Assignment for Chapter Dative Bonds Introduction: Familiar Reactions Solvation A reactive lone pair: the CO molecule CO and transition-metal atoms The Dative Bond: Summary Assignment for Chapter Delocalised Electronic Substructures: Aromaticity The Benzene Molecule Delocalised Electrons Environment-Insensitive π Substructures? Nomenclature and Summary Assignment for Chapter Appendix G Some Historical Considerations 203 G.1 Introduction

5 Contents ix G.2 The Hückel Model G.3 Commentary G.4 Consequences Organic and Inorganic Chemistry Commentary on Results Nitric Acid and Related Molecules The nitrate ion NO Carbonic Acid and Carbonates Sulphuric Acid and Sulphates Assignment for Chapter Further Down the Periodic Table The Effect of Increasing Atomic Number The Possible Demise of Lone Pairs A Particular Case: Sulphur The General Case: Hypervalence Single or double bonds? The steric effect How to Describe These Bonds? A comparison: 16 valence electrons An Updated Summary Assignment for Chapter Reconsidering Empirical Rules Limitations of the Octet Rule The Basis of the Octet Rule Population Analysis Resonance and Resonance Hybrids Oxidation Number Summary for Number Rules Assignment for Chapter Mavericks and Other Lawbreakers Exceptions to the Rules Boron Hydrides and Bridges The expected compound: BH The compounds which are found

6 x Contents Bridged, three-centre bonds Other Three-Centre Bonds? Metals and Crystals Metals Crystals The Hydrogen Bond Lawbreakers? Assignment for Chapter The Transition Elements The Background Transition Metals: Effects of d Electrons Screening in the Electronic Structure of Atoms History and Apology The crystal model The molecular orbital model The chemical model Apology Comments Assignment for Chapter Omissions and Conclusions Omissions Intermolecular forces Chemical reactions Conclusions Assignment for Chapter Appendix H The Pauli Principle, Spin and Electron Repulsion 289 H.1 Pauli and Electron Interactions H.2 Effects of Electron Spin H.3 Three Types of Spin Alignment Appendix I A Note About Unoccupied MOs 295 Help with the Assignments 299 Index 309