Chemistry: Structure and Dynamics

PREFACE

In 1989 the Division of Chemical Education of the American Chemical Society formed the Task Force on the General Chemistry Curriculum to foster the development of alternative introductory chemistry curricula. Chemistry: Structure and Dynamics is one of the products of the work of the Task Force.

This text has been designed to encourage innovation in the teaching of general chemistry by providing flexible materials that allow instructors to build a custom curriculum appropriate for their students. This flexibility has been achieved through the use of a core/modular structure. The core provides the fundamental concepts and principles that all students need to prepare them for the various degree programs in which the introductory chemistry course is a prerequisite. The course can then be customized to fit the needs and interests of the students being served by the addition of a variety of chapter appendices and modules selected by the instructor.

The philosophical basis for the modules is that it is more beneficial for students to investigate a few topics in detail than to be presented with a cursory survey of many topics. Short chapter appendices can be added to the chapters of the core. Modules can be inserted between chapters or at the completion of the core. In addition to providing the instructor with a sequence of material that meets the needs of a particular group of students, this arrangement also makes it easy to add material prepared by the instructor. Please note that this preliminary edition of the text consists of two volumes. Volume one contains the core and the chapter appendices. Volume two contains the modules. This structure allows the instructor to select the core and only a few chapter appendices and modules, and not to attempt to cover all chapter appendices and modules. The first edition of the text will have a format that will allow instructors to order a text containing only the core plus the chapter appendices and modules selected by the instructor.

The text is written for the introductory chemistry course for science and math majors. Its flexibility, however, makes it adaptable to most introductory chemistry courses. The development of this text has been based on the assumption that the vast majority of students who take this course are not chemistry majors and that, for them, general chemistry is the terminal chemistry course. The choice of concepts to include in the core is therefore based on two primary criteria. First, these concepts should be the most fundamental building blocks for understanding chemistry -- concepts that provide the basis on which remaining parts of the core and the modules are built. Second, these concepts should be perceived by the students as being directly applicable to their majors or careers.

Chemistry: Structure and Dynamics is characterized by the following key features:

It consists of a short core text accompanied by various modules. Volume one of this edition contains a core of approximately 600 pages with 75 pages of chapter appendices.

The text is flexible because modules can be added to the core to provide a curriculum that meets the needs of the students at a particular institution.

New models and current methods of understanding chemical concepts not yet found in traditional texts are used to introduce material.

Major themes are used to link the core material into a unified whole.

Organic and biochemical examples are used throughout the text to provide a more balanced coverage of all areas of chemistry.

There is an increased emphasis on conceptual questions and problems at the end of the chapters. A large selection of traditional problems are provided but these are supplemented with conceptual problems and discussion questions that ask students to explain, describe, or suggest experiments.

A chapter on chemical analysis that is unique to introductory texts has been included in the core. This chapter uses case studies to introduce students to the methods and tools that chemists use to solve real-world problems.

THE CORE

Traditional texts present concepts and principles in isolation, with little, if any, connection between each concept or principle and the rest of the material. Unifying themes are used to integrate the core topics in Chemistry: Structure and Dynamics.

One theme, which we call the process of science, incorporates experimental data in discussions that traditional texts present as the product of scientific process. Our goal is to provide students with the evidence that will allow them to understand why chemists believe what we do.

A second theme is the interrelationships between chemistry on the macroscopic and chemists on the microscopic scale. This is used to help students understand both how and why chemists make observations on the macroscopic scale so as to comprehend the microscopic world of atoms and molecules, and then use the resulting understanding of microscopic structure and properties to explain, predict, and -- most importantly -- control the macroscopic properties of matter.

• Atomic and molecular structure are developed early in the text and then repeatedly used to help students understand the physical and chemical properties of matter.

  
  
  

The fundamental concepts in the core portion of Chemistry: Structure and Dynamics can be found in current traditional texts. But these texts contain so much additional material that it is tempting to give too little time and emphasis to these fundamental concepts. As a result, the average student does not gain a full appreciation of the core concepts necessary to build a solid understanding of chemistry. Chemistry: Structure and Dynamics develops these core concepts using concrete models and then illustrates them with practical applications relevant to the students' experience.

THE CHAPTER, APPENDICES, AND MODULES

The chapter appendices extend the core material. The core chapter on bonding, for example, covers Lewis structures, molecular geometry, and the concept of polarity. A chapter appendix is then available that includes hybridization, valence bond theory, and molecular orbital theory. The modules are designed to introduce new topics, such as biochemistry, polymer chemistry, nuclear chemistry, and coordination chemistry.

The core/modular approach has advantages over both the traditional 1000-page texts and new "thin" texts. When traditional texts are used, sections or even whole chapters are skipped. This can be frustrating to those students who depend heavily on the text for understanding new material because later topics in the text are often explained using concepts that have been omitted. Chemistry: Structure and Dynamics avoids this problem by building the modules on the concepts presented in the core. The core covers all concepts that are prerequisite to the modules.

The core/modular approach also has advantages over the "thin" texts that have recently appeared. When one of these "thin" texts is used, the instructor is often frustrated because the text inevitably fails to cover a topic the instructor wishes to cover. By allowing the instructor to choose the chapter appendices and modules that will be included in the text, this frustration can be eliminated.

NEW MODELS

The new models used in this text can be divided into three types: data-driven models, models that reflect current understanding of chemical theories, and models that make it easier for students to understand traditional concepts. The development of electron configurations from experimental PES data is an example of a data-driven model that supports the unifying theme of the process of science by demonstrating to students how experimental data can be used to construct models. This approach gives students a more concrete, and still scientifically correct, foundation on which to base their understanding of electron configuration than does use of the more abstract quantum numbers. The use of experimental data and the graphical representation of that data to develop the gas laws is another example of this type of model. Once the kinetic molecular theory is developed it is used throughout the text to provide a consistent background for understanding temperature, heat, and equilibrium processes.

Models that reflect current understanding of chemical theories include the replacement of the VSEPR theory for predicting molecular geometry with Gillespie's more recent electron domain (ED) theory and the use of bond-type triangles to explain the interrelationship of covalent, ionic, and metallic bonding. Bond-type triangles are then used in the text to help explain physical and chemical properties of compounds and to predict properties of new materials.

New models in this text are also used to present familiar concepts in innovative ways that make it is easier for students to understand. For example, enthalpies of atom combination replace enthalpies of formation. Because chemistry is concerned with the making and breaking of bonds, thermochemical calculations are first done by considering the energetics of breaking the bonds necessary to produce atoms in the gas phase and then allowing these atoms to combine to form molecules. In the enthalpy of formation approach the standard states are the elements in their stable states of aggregation. This construct places another concept between the student and the idea that chemical reactions liberate or absorb heat through the making and breaking of bonds. The major strength of the atom combination method is the use of the powerful visual model of reactants being broken down into gaseous atoms and then recombining to form products. The advantage to this method is that bond breaking always requires an input of energy, whereas bond making produces energy. Instructors accustomed to thinking of enthalpy changes in terms of enthalpies of formation may at first find this method more awkward than enthalpies of formation. However, students find this approach much easier to visualize than enthalpies of formation.

A major advantage of the atom combination approach is that the same standard states and reaction diagrams are used for all thermodynamic parameters. Third law entropies are always used in conjunction with enthalpies based on elemental standard states to introduce free energy. The use of third law entropies that are based on yet a different concept and standard state further confuses students. The atom combination approach clearly shows students the origin of the entropies of substances, and because of the direct relationship with enthalpies and free energies makes all these concepts more accessible to students.

Another example of the use of models that reflect current understanding of chemical theories is the introduction of average valence electron energies (AVEE), calculated from PES data, which describe how tightly an atom holds on to its electrons. AVEE values are used to predict which elements will form cations and which will form anions. This value is then used to develop the concept of electronegativity, thus giving electronegativity a more concrete meaning for students. Not only do the students develop the electronegativity concept from the same data used to determine the electronic structure of atoms, but they also see how electronegativities relate to oxidation numbers, partial charges, and formal charges. This theme is carried through the text and provides a unifying thread for oxidation-reduction, resonance structures, and polarity.

The final chapter of the core introduces students to the types of real problems that chemists can help solve and to the instruments they use to do so. Although most of the students in the typical introductory chemistry course are not chemistry majors many of them will have careers that will require them to interact with chemists. Most of these interactions will involve analysis of samples. This chapter introduces how samples are analyzed and some of the major tools which chemists use. Case studies representing problems from a variety of fields have been used to present real-world problems. This chapter is not meant to emphasize instrumental analysis or spectral interpretation. Instead it is meant to make instruments seem less like black boxes and the interpretation of spectra seem less like magic.

USE OF THE CORE TEXT AND MODULES

The core text consists of the first fifteen chapters found in Volume one. The core may be supplemented using the chapter appendices (found in Volume one at the end of Chapters 4, 6, 7, 10, 11, 12, and 14) or modules (found in Volume two).

The chapter appendices extend the core topics found in the chapters they accompany. The material in the chapter appendices may be used or skipped at the discretion of the instructor since subsequent core chapters depend only on the concepts covered in the core chapters. Topics covered in the core chapters and their accompanying appendices are listed in the table of contents.

Although the modules are located in the second volume, they may be inserted at various points in the text depending on the core material prerequisite to the modules. The table below lists the core chapters that are prerequisite for each module.

Prerequisites for Modules (Volume Two)

Module Prerequisite Core Chapters

Biochemistry Chapter 11 and Organic Module

Complex-Ion Equilibria Chapter 11

Materials Science Chapter 9

Chemistry of the Nonmetals Chapter 12

Nuclear Chemistry Chapter 14

Organic Chemistry Chapter 7

Polymer Chemistry Chapter 7, Organic Module & Chapter 4 Appendix

Solubility Equilibria Chapter 11

Transition-Metal Chemistry Chapter 5 & Chapter 4 Appendix

THE ROLE OF THE PRELIMINARY EDITION

This preliminary edition of Chemistry: Structure and Dynamics is part of a work in progress. It is only through classroom feedback from instructors and students that a thoroughly tested and reviewed first edition of this text can be published. By filling out the questionnaires that follow each chapter you can ensure that the published text will be complete, accurate, and useful to beginning chemistry students.

TO THE STUDENT

You are part of an experiment in the teaching of beginning chemistry. This text, Chemistry: Structure and Dynamics, differs from most text currently available for introductory chemistry. The text contains a short core of material that should provide a basis for the understanding of the fundamental concepts of chemistry, and new models to teach familiar concepts in ways that should make these concepts easier to grasp. There are consistent themes running throughout the text which tie together many seemingly isolated topics.

We would greatly appreciate your help as the first group of students to use this preliminary edition. Please complete the questionnaire that follows each chapter. We are eager to incorporate your comments and suggestions, and thank you for sharing in the production of a new textbook.