The Chemical Educator
© 1998 Springer-Verlag New York, Inc.
I classroom-tested the preliminary edition of the Bodner, Rickard, and Spencer core text, Chemistry Structure & Dynamics, in Integrated General Chemistry I, (26 students) and Integrated General Chemistry II, (18 students) in the fall of 1995. Eight students were enrolled in both courses. I assigned the first 14 chapters in the textbook, and three sections from Chapter 15 (Interaction of Electromagnetic Radiation with Matter—Spectroscopy, The Fox River Mystery, and Dead Cats) in conjunction with laboratory experiments in the two courses.
For each chapter, I recommended a subset of the end-of-chapter problems. I have mixed feelings about having answers to problems provided. Students like them because they provide the feedback of the "correct" answer, telling students that they are on the right track. However, it relieves them of the responsibility of judging whether their answer is reasonable (something they will have to do, or should be doing, on exams). Learning to make such judgments is an important skill to develop. Furthermore, having the answers available gives the strong impression that there is one right answer and that any other answer must be wrong. Sometimes the answers in the back of the book are wrong, at least from my perspective. All this places too much emphasis on the answer and not enough emphasis on how one gets to it. In addition, I like having some problems that have a range of possibilities for answers. Having the Instructor's Manual, but not having the answers to problems presented in Appendix C, would give the instructor the flexibility of deciding how answers would be made available to the students. It increases the instructor's responsibility for giving students feedback, but that is a responsibility the instructor should take seriously. Both the students and I would appreciate having brief solutions to the checkpoints in the back of the text. Ideally they are pausing to think about the checkpoints when studying the text and, here, it would be helpful to be able to check and see whether they are thinking along appropriate lines.
Before my comments on the core text, I will relate two general comments from students. An unprecedented number of students purchased their own periodic table; and there were repeated complaints about the core text not having a periodic table that included atomic masses. Other comments, more laments than complaints, concerned the absence of color illustrations and pictures. There is something inviting about a text with color illustrations and pictures, and students missed them. I didn't mind at all, nor did I see students objecting to a softbound chemistry text. If they were asked to choose between a lower cost text without color illustrations and pictures, and a text with them that costs significantly more, I think the lower cost might be the preferred choice. In this multimedia age with the World Wide Web, instructors can provide attractive and colorful visuals to supplement the core text. I did this only minimally using the preliminary edition of the core text, as I was kept busy mastering the new approaches to teaching general chemistry in the core text. Having gone through the course with the text once, I certainly would be better able to provide the students with colorful supplementary visuals in the second go-around.
Chapter 1 (Elements and Compounds) and Appendix
I supplemented Appendix A with a seven-page presentation of simple statistics that the Colorado College chemistry department has prepared and includes with its laboratory manual for the course. I believe that statistical analysis of numerical and experimental data is an important skill for students in general chemistry.
I was glad to see a discussion of scanning tunneling microscopy included in Chapter 1. As I noted above, the presentation of the periodic table with only atomic numbers, was considered inadequate by almost all students.
Chapter 2 (The Mole)
The figures in this chapter are helpful. The presentation of a sequence of steps for solving limiting reagent problems is an effective method of presentation, particularly because it is good modeling of how to solve chemical problems. Perhaps by the authors stating explicitly (a) that they are modeling a way of solving chemical problems, (b) that they are going to continue this modeling practice throughout the text, and (c) by encouraging the student to develop their own sequence of steps for solving different types of chemical problems, the text could get students practicing this important discipline more extensively.
Chapter 3 (The Structure of the Atom)
Incorporating photoelectron spectroscopy and the energy structure of atoms is a big plus, but more emphasis should be placed on the fact that it is the energy structure that is being revealed.
I am less enamored of the use of the shell model and would prefer that the authors talked about orbitals as representing energy levels and spatial distributions of electrons, instead. A statement such as "one electron occupies the outer shell" combines energy level and spatial distribution in a way that is conducive to student misconceptions in the visualization of electrons in atoms. I would be happier if the authors presented orbitals and orbitals diagrams rather than shells and shell diagrams.
At first I did not see the necessity of introducing the new (to me) concept of average valence electron energy (AVEE). However, it has value in distinguishing between metals, nonmetals and semimetals. I tried using first ionization potentials for this purpose, and it did not work. So, if you want to give some meaning to that stair–step line on the periodic table (which I do), AVEE is apparently the way to do it. Using this concept also provides a reason for paying attention to electronic energy levels in atoms.
Chapter 4 (The Covalent Bond)
One of the very positive aspects of the core text is the introduction and relating of equations for calculating formal charge, partial charge, and oxidation number for atoms in molecular species from the electronic structure of the molecular species. It very effectively ties together these three ways of counting electrons.
I also like the use of the modified version of the VSEPR theory, the electron-domain (ED) theory. I have been using a similarly modified form of the VSEPR theory myself, but lacked a good term for electron bonding and nonbonding regions; electron-domain theory does the job very nicely. Most of the students in the first course reported that they had mastered ED theory to predict the geometry of molecular species, and their performance on examinations indicated that they had. Section 4.15 (The Role of Nonbonding Electrons in the ED Theory) is very important. I think it really helped my students distinguish between electron domain geometry and molecular geometry, which heretofore has typically been a problem for them.
It is good that molecular orbital theory was placed in the Special Topics section of Chapter 4 . I have found that most students get very little understanding of it in the general chemistry course and do not really use it until they get to an advanced (junior- or senior-level) chemistry course. Thus it was easy to bypass with the core text.
Bonding conceptualized as overlapping of atomic orbitals, including hybrid atomic orbitals, is another matter, since bonding is commonly conceptualized in this way in organic chemistry. Either we introduce students to this bonding model in general chemistry, or we give that responsibility to teachers of organic chemistry, and inform them that we are doing so. Though the trend at Colorado College has been to decrease the emphasis on this topic in general chemistry, our organic chemistry instructors still expect it to be introduced in general chemistry. In doing so, I found that I had to go over this with students several times and supplement what is presented in the core text with drawings, models, and a handout.
If one does have to introduce this topic, then the way and extent to which the core text presents it could be significantly improved. As I have indicated, I would prefer having the core text introduce the concept of orbitals (particularly shape and orientation in space), in place of shells. I believe I was helped significantly in enabling students to get a handle on this topic by having introduced them to orbitals and their shape and orientation.
I am in a quandary as to how far we should go into hybrid orbitals in general chemistry. It seems to me that either we should leave it out, or go into it far enough in our general chemistry texts that students can derive reasonable understanding from the text. As it stands, the core text, by placing an inadequate presentation in a Special Topics section, and by not really presenting orbitals in Chapter 3, paves the way for leaving it out.
Chapter 5 (Ionic and Metallic Bonds)
I very much like the introduction of bond-type triangles in this chapter. Both the students and I would have been helped in our understanding if the presentation of the process by which one assigns a binary compound to different regions of the triangle had been clearer.
Listing the rules for determining oxidation number in order of priority helps students assign oxidation numbers. Unfortunately the core text does not do that. I very much like the inclusion of the method of assigning oxidation numbers from Lewis electronic structures and electronegativities.
Chapters 6 (Gases) and 7 (Making and Breaking
I am intrigued by the definition of heat as energy in transit. I decided to teach using this definition, and was satisfied with the way it worked. It was a helpful correction on my thinking, since I had been prone to consider a system or object as containing heat energy. I like the connection made between heat and the kinetic molecular theory, reinforcing the importance of presenting the kinetic molecular theory in the previous chapter. The one place I had to supplement this chapter was in the area of calorimetry. I did so by using a laboratory experiment involving calorimetry.
I very much like the calculation of enthalpies of reaction using enthalpies of atom combination, and would find it hard to go back to using enthalpies of formation now that I have worked with enthalpies of atom combination. I did not assign and we did not use the Chapter 7 Special Topics on Hess's law and enthalpies of formation, and neither I nor the students seemed to miss not having discussed Hess's law or enthalpies of formation. I prefer enthalpies of atom combination because they are directly related to bond forming and bond breaking, and because having the zero state in enthalpies of atom combination be the free gaseous atom of each element is both simpler and more coherent than having the zero enthalpy of formation be its most thermodynamically stable form. This latter definition of a zero enthalpy of formation requires that you know what the thermodynamically stable form is: solid, liquid, gas, etc. With enthalpies of atom combination, the zero state is the same for all(!) elements: the element in its monoatomic gaseous state. This is a significant advantage and simplification, and it should be stated more explicitly in the chapter, rather than being assumed or relying on the reader discovering this from the table in Appendix B.
Chapter 8 (Liquids and Solutions)
Pictures really do help in this chapter. However, I wish there were a special topics section on colligative properties. I missed having that topic available for study.
Chapter 9 (Solids)
Section 9.3 on ionic solids was helpful in reinforcing the concept of enthalpy of atomization through the calculation of lattice energies. However, something should be said about the sign problem associated with electron affinities, where the exothermic process (which electron affinity typically is) is, by convention, a positive value, and is so listed in Table B.6. Section 9.3 gives the name electron affinity to the process of adding an electron to an atom, but then states that it is usually an exothermic process and gives it a negative value. This is particularly a problem with Problem 8 at the end of the chapter, where the enthalpy change for the reaction O(g) + 2 e- ® O2- is correctly given as +448 kJ/mol, but without any comment as to why this electron affinity process is positive. The result was a fair amount of student confusion, which could have been avoided if note had been made of the anomalous sign convention used for electron affinities. How about reversing the anomalous sign convention for electron affinities to make it consistent with the sign convention for the rest of thermodynamics? Could this bold new text be bold in that respect as well? I liked the way that this chapter reinforced the use of the bond-type triangle, both in Section 9.1 and in problems at the end of the chapter.
Chapter 10 (An Introduction to Kinetics and
I like the fact that this chapter on equilibrium begins first by talking about reactions not necessarily going to completion, and by introducing both kinetics and equilibrium before it goes on to concentrate on equilibrium, leaving kinetics for Chapter 14.
I would change how the text introduces the equilibrium constant. It is my experience that students become overwhelmed by all the capital K's that are presented to them: Kc, Ka, Kb, Kp, Kw, Ksp, etc. They accept them as constants in different contexts, but seem to forget that all are equilibrium constants. It would help if, when the text first introduces the equilibrium constant, it does so not as Kc, but as Keq. Then whenever it introduces an equilibrium constant with a new subscript, it could remind the reader that this is just another version of an equilibrium constant. Kc is not Kp, but both Kc and Kp are equilibrium constants, Keq. I believe it would also help the student making the connections among the various equilibrium constants if there were more than just the two equilibrium constant expressions at the end of Chapter 10 that involve concentrations of species in (aqueous) solution. If there were more aqueous phase examples interspersed among the gas phase examples, then the transition to Ka and Kb as just further examples of equilibrium constants would be easier.
The section on rules for writing equilibrium constant expressions is another good example of modeling the writing-out of a strategy or procedure for solving a chemical problem. Students recognize and appreciate that, and should be encouraged to emulate it when tackling chemical problems.
The introduction of the concept of Q is helped significantly by the earlier introduction of brackets to represent equilibrium concentrations, and parentheses to represent concentrations at any moment in time other than equilibrium. I also like the DC notation introduced in this chapter.
I assigned Chapter 10 Special Topics and thought it was essential to do so. Both the students and I found it very helpful in working with equilibrium problems. The discussion of the effect of changes in pressure on gas-phase equilibria was not very helpful, and the students had difficulty with it. Section 10.11 is important in preparing the student for working with equilibria in reaction systems that involve more than just gases. I think it would help to expand it somewhat, particularly with some additional examples.
Figures 11.1, 11.2, 11.4, and 11.8 seem to suggest we are going backwards in our understanding of solutions. Section 11.11 is an important section that builds upon what has been presented, particularly in Chapter 4, on the structures of molecules. The section on pH titration curves is just enough to be sufficient. I did assign the Chapter 11 Special Topics, and it was encouraging to see in it the simplifying assumptions working, making solving acid–base equilibria problems seem manageable.
Chapter 12 (Oxidation–Reduction Reactions)
I very much like the rules for determining when an element can act as an oxidizing and/or reducing agent. However, I missed having electrochemical cell notation, such as [Zn(s) | Zn2+(aq) (1 M) || Cu2+(aq) (1 M) | Cu(s)], introduced in this chapter. I also missed any illustration of the direction of ion flow in electrochemical cells correlated with concentration gradients that develop as the cells are operated. The discussion of the electrolysis of aqueous NaCl is good.
In teaching students the half-reaction method for balancing oxidation–reduction equations, I reversed the order of balancing atoms and balancing charge from that given in the core text. I found that the students had more difficulty in balancing the half reactions following the order in the core text.
Chapter 13 (Chemical Thermodynamics)
I like beginning the discussion of entropy with a discussion of it as a measure of disorder, and the poker-hands example. I am glad that the equation DSuniv = DSsys+ DSsurr is given in presenting the second law of thermodynamics. I recommend that the authors show how that equation can be rearranged to give another important equation in this chapter, DG = DH – TDS.
My newly acquired preference for enthalpies, free energies, and entropies of atom combination is reinforced by the fact that the zero standard state is the same for all the standard state functions: the monoatomic element in the gaseous state. It would be hard to go back to enthalpies, free energies, and entropies of formation, given this simpler, more coherent approach based on atom combination. Given that there are now DS's of 0, it is essential in presenting the third law of thermodynamics that the distinction between change in entropy, DS, and absolute entropy, S, be made crystal clear.
I missed having a discussion in this chapter of the enthalpy, entropy, and free energy changes associated with phase changes, both at the temperatures at which they occur when they are reversible processes in equilibrium, and at temperatures above and below the equilibrium phase change temperature when they are spontaneous in one direction or the other. This could be effectively discussed in Section 13.8 (The Effect of Temperature on the Free Energy of a Reaction).
Chapter 14 (Kinetics)
I polled the students on how they felt about having kinetics (beyond the introduction in Chapter 10) as the last chapter we covered. I did this because the Colorado College chemistry department has, for the last several years, been starting the second half of general chemistry with kinetics. Of the 17 students responding, 14 were satisfied with having it at the end, two would have preferred it at the beginning (in one case, at the very beginning of general chemistry!), and one was uncertain. Among the reasons satisfied students gave for preferring it at the end were:
I found that I had to frequently work with students to help them decide when it was appropriate to use the non-integrated form of the rate law, and when it was appropriate to use the integrated form in solving kinetics problems. It would help if:
Some Student Input
I polled students about which chapter in the second half of general chemistry was the easiest for them, and which was the hardest. (They studied Chapters 10–14.] The only chapter not listed as easiest was Chapter 11 (Acids and Bases). The one most commonly listed as easiest (9 out of 17 times) was Chapter 13 (Chemical Thermodynamics). This, despite the fact that just over half of the class had been introduced to thermodynamics in a section of the first half of general chemistry, which used the approach of Hess's law and enthalpies of formation. There was no consensus on which chapter was the hardest.
In some sense I approached the preliminary edition of the core text as a student myself. I found it stimulating, and learned new ways to approach material that I have been teaching for 28 years.
The Modular Chapter
I did not use the modular chapter accompanying Chemistry: Structure & Dynamics. The two semesters of general chemistry were full enough with the 14 chapters of the core text that were used. I perused Module 3 (Materials Science), Module 5 (Nuclear Chemistry), and one section (Lewis Acid–Lewis Base Approach to Bonding in Complexes) of Module 9 (Transition Metal Chemistry). The Lewis acid–Lewis base discussion is too terse and too narrowly tied to coordination complexes to be of general use in cutting across transition metal chemistry, acid–base chemistry, and organic chemistry.
In the nuclear chemistry module, the applications sections (N-8 through N-14) and the "Neutron-Rich versus Neutron-Poor Nuclides" section contain much good information and are well written. In the materials science module, the "Unit Cells" and "Defects" sections are particularly effectively presented and give considerable insight into crystal structures.