Principles of Modern Chemistry 8th Edition

Book Preface

The eighth edition of Principles of Modern Chemistry is written for students in honors and upper-mainstream general chemistry courses who seek to under-stand and interpret chemical events at the molecular level. The relation of mo-lecular structure to function and properties requires the introduction of molecu-lar structure early in the course and the use of structural arguments in presenting the remaining topics. Moreover, students will soon be introduced to the predic-tive power of chemical computations and simulations, for which a solid back-ground in the description of molecular structure is essential.
The organization of the eighth edition is fundamentally the same as that of the seventh edition, and presents the material from a unified, molecular point of view that continues to emphasize the central role of structure, but with greater focus on the electronic structure of molecules as a unifying theme. This edition also deepens and broadens the introduction of chemical principles in several chapters. Recognizing that in the top colleges and universities that use this text, over 90% of students taking introductory chemistry have taken a single-variable calculus course in high school, or are taking calculus as a co-requisite for the course, we have improved several portions of the text. These revisions include a more quantitative treatment of the forces and potential energy in molecules (Chapter 3), dipole moments (Chapter 3), molecular collisions (Chapters 9 and 18), and the Maxwell-Boltzmann distribution of molecular speeds (Chapter 9). The eighth edition also includes major revisions in the chapters on quantum mechanics and molecular structure (Chapter 6), electrochemistry (Chapter 17), nuclear chemistry (Chapter 19), and molecular spectroscopy and photochemis-try (Chapter 20).
Significant Changes in This Edition

■ OWLv2 for General Chemistry—Our online learning solution OWLv2 has been revised to offer more flexible student and instructor functionality, new personalized study tools, enhanced integration with learning management sys-tems, and improved analytics. OWLv2 includes Quick Prep, new iPad-compatible visualizations, tutorials, and simulations, and new Adaptive Study Plans. Tutors, Visualizations, and Simulations have been converted from Flash to HTML, allowing for easier navigation and streamlined grading.
■ Revised Writing Style without Loss of Rigor—The language is more modern and less formal. We have introduced a more conversational writing style, designed to engage our students as active participants in developing the pre-sentation. We have examined every sentence in the book to simplify and lighten the language without compromising intellectual integrity.

■ Greater Flexibility in Topic Coverage—In response to comments by stu-dents, faculty, and reviewers, greater modularity and flexibility have been built into the text to make it compatible with alternative sequences of topics. While keeping the discussion of bonding and structure at the beginning of the book, we have been careful to maintain the option to follow the “macro-to-micro” approach used in previous editions. Selecting alternative approaches is facilitated by the unit structure of the book; we offer several suggestions in the Teaching Options section.
■ Streamlined Topic Coverage—In response to suggestions by both users and reviewers of the text, we have taken care in this revision to retain only those topics that were felt to be critical for students. Chapters 19 and 20, espe-cially, were shortened after extensive surveying of professors who teach the course; what remains (we think) are chapters that are more readily covered within the framework of a conventional two-semester course.
■ New Problems—We’ve added approximately 30 new and revised problems throughout the book. These follow the unique tradition established in previ-ous editions that all problems are based on actual experimental data mea-sured on real chemical systems. We intend the problems to guide our students in developing intuition for chemical results and the magnitudes of chemical quantities, as well as facility in numerical calculations.

Or ganizational Approach for Selected
Chapters and Major Changes to Content
for Eighth Edition
Chapter 1: The Atom in Modern Chemistry
This chapter describes the physical structure of the atom, as determined from the classic experiments of Thomson, Millikan, and Rutherford. For this edition, we added an introduction of the electrostatic force on negatively and positively charged particles (see Section 1.4.3), improved the coverage of the J.J. Thompson experiment measuring the charge-to-mass ratio of the electron (see Section 1.4.3), and incorporated coverage of the mole, counting molecules by weighing (which was Section 2.1 in the seventh edition; it is Section 1.6 here in the eighth edition).
Chapter 3: Atomic Shells and Classical Models
of Chemical Bonding
This chapter provides a substantial introduction to molecular structure by cou-pling experimental observation with interpretation through simple classical models. Today, the tools of classical bonding theory—covalent bonds, ionic bonds, polar covalent bonds, electronegativity, Lewis electron dot diagrams, and VSEPR theory—have all been explained by quantum mechanics. It is a matter of preference whether to present the classical theory first and then gain deeper in-sight from the quantum explanations, or to cover the quantum theory first and then see the classical theory as a limiting case. Our experience has been that presenting the classical description first enables our students to bring consider-ably greater sophistication to their first encounter with quantum mechanics and therefore to develop a deeper appreciation for that subject. We have seen that this approach offers definitive pedagogical advantages by enabling students to

■ learn the language and vocabulary of the chemical bond starting from famil-iar physical concepts.

■ become familiar with the properties of a broad array of real molecules before attempting to explain these results using quantum mechanics.
■ develop experience in using physical concepts and equations to describe the behavior of atoms and molecules.

We have organized this chapter to meet these goals. Changes for the eighth edi-tion include the following:

■ The chapter now presents attractive and repulsive forces between nuclei and electrons, and between atoms in a diatomic molecule, using simple vectors in two dimensions, so that students may correctly calculate the direction of attractive and repulsive forces between particles (see Section 3.3). We emphasize the physical insight gained from the new quantitative treatment.
■ We have streamlined and improved the discussion of polar covalent bond-ing, removing the application of the virial theorem but retaining the basic description of Coulomb forces between electrons and nuclei (see Sections 3.7 and 3.9).
■ We introduce the direction of a molecular dipole moment, in addition to its magnitude (see Section 3.9.4).

Chapter 4: Introduction to Quantum Mechanics
This chapter presents a significant introduction to the concepts and vocabulary of quantum mechanics through very careful choice of language, illustrations with experimental data, interpretation with aid of simple models, and extensive use of graphical presentations.
For the eighth edition we improved the treatment of the particle-in-a-box with examples (Example 4.7 and the solution to Problem 37) that show students how to use the mathematical solutions to answer questions about the prob-ability of the electron being found in different regions of space. We chose the chemical system of 1,3-butadiene for the example. The added material (mainly in Section 4.6) is appropriate both for students who have had integration in their single-variable calculus course and for students who would simply estimate the area under a curve graphically.
Chapter 5: Quantum Mechanics and Atomic Structure
This chapter provides a comprehensive introduction to the hydrogen atomic orbitals, the Hartree orbitals, the shell model of the atom as explained by the Hartree orbitals, and the relation of the shell model to experimental measure-ments such as photoelectron spectroscopy and the periodic properties of atoms. In this edition, recognizing that students’ quantitative understanding of electron density in molecular systems begins with their introduction to atomic wave functions, we added graphical and analytical examples (Examples 5.2 and 5.3) to help students navigate the three-dimensional coordinate system in atoms (see Sections 5.1.2 and 5.1.3). Equation 5.7 reduces the integration over three di-mensions to an integral that students may solve using single-variable calculus (or estimate graphically) to aid their understanding of the graphs of r22 and r2R2 presented in the chapter.

Chapter 6: Quantum Mechanics and Molecular Structure
This chapter provides a gentle ramp-up, starting from a qualitative overview of the quantum picture of the chemical bond and its relation to the potential energy curve for a molecule. The discussion proceeds through molecular orbital theory (MO), then valence bond theory (VB), then the combined use of MO and VB, and ends with a comparison of MO with VB. Changes for this edition include:

■ The pedagogy in the introductory section titled Quantum Picture of the Chemical Bond (Section 6.1) has been shortened and improved.
■ The graphics and equations presented in the treatment of LCAO-MO theory (see Sections 6.5 and 6.6) have been revised to represent constructive and destructive interference using the same wave functions that are presented in Chapter 5. The linear combinations of atomic orbitals used to construct hybrid atomic orbitals (Section 6.9) have been revised and the pedagogy is shortened and improved.
■ The treatment of polyatomic molecules has been improved, including delo-calized p bonding in NO2, 1,3-butadiene, and benzene.
■ The summary and comparison of LCAO-MO theory and the valence bond model was shortened and improved (Section 6.12).

Chapter 7: Bonding in Organic Molecules
The purpose of this chapter is to describe the bonding and nomenclature in al-kanes, alkenes, alkynes, aromatics, and conjugated hydrocarbons and in the ma-jor functional groups. Our main goal is to illustrate the bonding theories from Chapter 6 with examples from organic chemistry that can be used in conjunc-tion with Chapter 6. For the new edition we updated the nomenclature to give IUPAC names (retaining the common names where advisable) and moved the graphics related to delocalized p molecular orbitals in 1,3-butadiene and ben-zene to Chapter 6.
Chapter 8: Bonding in Transition Metal Compounds
and Coordination Complexes
We present a comprehensive introduction to bonding in transition metal com-pounds and coordination complexes using MO and VB theory as developed in Chapter 6. Our goal is to demonstrate that MO theory is not limited to the first- and second-period diatomic molecules and that it provides the most satisfactory method for describing bonding in coordination complexes. The material covered in this chapter now provides a self-contained introduction to structure and bonding in inorganic chemistry that should provide sound preparation for an advanced inorganic chemistry course. For the new edition, we have revised and improved the figures related to chiral molecules (see Section 8.3.3) and crystal field theory (see Section 8.4.2).
Chapter 9: The Gaseous State
In this chapter we improved the treatment of the Maxwell-Boltzmann distribu-tion of molecular speeds (see Section 9.5.2) to help students estimate the fraction of molecules with speed in a given range and to understand why the rate of a chemical reaction might increase with temperature. We also introduced the con-cept of relative velocity in the treatment of molecular collisions (see Section 9.7.2) so that students have a basis for deriving (in Chapter 18) the expression for the rate of an elementary bimolecular reaction in terms of the product of the concentrations of the two reacting species.
Chapter 10: Solids, Liquids, and Phase Transitions
For the eighth edition, we have introduced calculus to the treatment of com-pressibility and thermal expansion (see Sections 10.1.2 and 10.1.3).
Chapter 12: Thermodynamic Processes
and Thermochemistry
The treatment in this and prior editions gives the instructor flexibility on how to cover traditional thermochemistry in conjunction with direct applications of the laws of thermodynamics. Stronger students may be encouraged to solve problems starting from the axioms and deriving the needed formulas from first principles.
Chapter 13: Spontaneous Processes
and Thermodynamic Equilibria
The chapter presents a molecular statistical interpretation of entropy alongside the traditional macroscopic description involving the reversible transfer of heat. It carefully develops the conditions under which one may use the change in Gibbs free energy to assess the spontaneity of a reaction.
Chapter 14: Chemical Equilibrium
To provide flexibility for instructors, this chapter is written to allow thermody-namics to be taught either before or after equilibrium. Each topic is introduced first from the empirical point of view, and then followed immediately with the thermodynamic treatment of the same topic. Instructors who prefer to treat thermodynamics first can use the chapter as written, whereas those who prefer the empirical approach can skip appropriate sections, and then come back and pick up the thermo-based equilibrium sections after they cover basic thermody-namics. “Signposts” are provided in each section to guide these two groups of readers; the options are clearly marked. Specific examples of this flexible ap-proach are:

■ Section 14.2 provides a thorough discussion of procedures for writing the empirical law of mass action for gas-phase, solution, and heterogeneous reactions, with specific examples for each.
■ Section 14.3 follows with the thermodynamic prescription for calculating equilibrium constants from tabulated Gibbs free energy values for gas-phase, solution, and heterogeneous reactions, with specific examples for each. For students who have covered Chapters 12 and 13, it gives a succinct derivation of DG 5 DG° 1 RT ln Q and the relationship between Q and K.
■ Sections 14.4 and 14.5 present a variety of equilibrium calculations based on the empirical law of mass action.
■ Section 14.6 discusses direction of change in terms of the empirical reaction quotient Q, with illustrations in gas-phase, solution, and heterogeneous reactions.
■ Section 14.7 discusses direction of change from the point of view of thermo-dynamics, relating Q to the Gibbs free energy change and the equilibrium constant.

Chapter 15: Acid–Base Equilibria
The examples establishing the molecular-level interpretation of acid-base equi-libria (see Section 15.8) have been carefully vetted and improved.
Chapter 17: Electrochemistry
This chapter provides a molecular level interpretation of electrochemical pro-cesses unique in an undergraduate textbook, as far as we are aware, to comple-ment the standard thermodynamic treatment of the subject. We introduce the idea that a redox potential (a free energy) can be associated with an orbital en-ergy level, which allows us to use energy-level diagrams to help students visual-ize electron transfer processes pictorially. This approach also allows us to intro-duce an electrostatic driving force for electrochemical processes and connect it to the thermodynamic driving force. We explicitly identify the conditions under which this approximation is valid (outer sphere electron transfer processes, neg-ligible entropic contribution to the Gibbs free energy) so that our students can use this description with confidence.
For the eighth edition we streamlined and improved the introductory mate-rial on electric potential versus potential energy (see Section 17.1), moved the essential material on the molecular interpretation of electrochemical processes to later sections in the chapter to better integrate the pedagogy and applications, and deleted the long subsection on alternative reference electrodes in Section 17.2, moving the essential material to earlier in Section 17.2. We revised the ap-plications in the molecular electrochemistry section (which was Section 17.5 in the seventh edition and is now Section 17.4 in the eighth edition) to shorten the presentation and improve clarity, including the discussion of using semiconduc-tors in solar cells for generating H2 as an alternative fuel.
Chapter 18: Chemical Kinetics
For the eighth edition we revised and improved the treatment of collision theory (see Section 18.6.1) to allow students to solve problems of importance in atmo-spheric chemistry, such as the reaction of Cl with methane. The concepts of rela-tive velocity and impact parameter are developed with new graphics and simple examples (Examples 18.9, 18.10, and 18.11) and the connection with molecular collisions (as introduced in Chapter 9) are firmly established. We also expanded the material on molecular beam experiments (see Section 18.6.4). The seventh edition subsection on mechanisms of enzyme-catalyzed reactions is now pre-sented as a Connection to Biology.
Chapter 19: Nuclear Chemistry
Chapter 19 has been extensively reorganized and streamlined, with the focus now on balancing nuclear reactions, mass–energy relationships, and predicting the spontaneity of nuclear reactions (with improved notation in the eighth edi-tion), and the kinetics of radioactive decay. This material is followed by a de-tailed description of selected key applications. The first set of applications, cov-ered under the heading, Radiation in Biology and Medicine (see Section 19.4), retains the Connection to Medicine presented in the seventh edition. The chapter ends with applications in nuclear fission, including nuclear power reactors (see Section 19.5.1), and fusion (in the sun and other stars and in proposed energy applications).