Elements of Curriculum Reform: Putting Solids in the Foundation

Chemical Education Today

Award Address

Elements of Curriculum Reform: Putting Solids in the Foundation 1997 George C. Pimentel Award, sponsored by Union Carbide Corporation Arthur B. Ellis Department of Chemistry, University of Wisconsin–Madison, Madison, WI 53706 I am honored to receive the George C. Pimentel Award in Chemical Education from the American Chemical Society. In many ways, the volume Opportunities in Chemistry, which was created through Pimentel’s leadership, provided the blueprint for the curriculum reform project I want to tell you about today (1). This project has involved several dozen individuals from across the country, whose contributions I want to recognize, as well. What I will do is summarize the project for you, describe some of its recent developments, and discuss some of its broader implications. If you have read Opportunities in Chemistry, you cannot help but be impressed by the vitality of our community’s research enterprise: the developments in research over the past few decades have been simply breathtaking. We can now image individual atoms and push them around, almost at will. We can establish and manipulate enormous databases that help us better understand our environment. We can find our way to a lecture hall using global positioning systems. And we can even clone a sheep named Dolly! Opportunities in Chemistry insists that our educational enterprise needs to have the same vitality as our research enterprise. Among the numerous cutting-edge research areas identified by Pimentel’s book, many involve the solid state. Yet, until recently, solids were a relatively small part of the chemistry curriculum. Helping to close this particular gap between the research and educational enterprises was the objective of our Ad Hoc Committee for Solid-State Instructional Materials, formed in 1990.1

Topic Redox

Chapter 2

Semiconductors Smart Materials Solid Solutions

9 10 3

5

7 8

1 2 3

6 7

9 10

7 8 3

5

8, 11 2, 7, 9

9

Spectroscopy Beer’s Law Stoichiometry

Experiment

10 3, 7, 14 7, 9

9 10

2, 11

Figure 1. Excerpt from the topic matrix in the Companion , ref. 3. Topics commonly discussed in introductory chemistry courses are listed in the left-hand column. The rows of the matrix identify corresponding chapters and laboratory experiments that provide solidstate examples of the topics.

In launching this project, our committee identified many reasons why solids should be an integral part of the curriculum (2): •

•

•

•

•

Solids provide recognizable examples. The macroscopic properties of copper wire, diamond, and table salt, for instance, are well known by our students and represent an excellent starting point for introducing an atomicscale view of matter. Students also routinely encounter high-tech materials and devices, which provide “hooks” to the core chemical concepts. Solids are the basis for many technical careers. Materials like polymers, ceramics, metals, and semiconductors are critical components of a multitude of advancing technologies. Early exposure to these solids is appropriate career preparation. Solids provide a means for enhancing skills. Extended solids, for example, promote visualization skills. The ability to construct analogies is developed by the use of examples that are complementary to and that reinforce traditional molecular examples. Solids help to establish interdisciplinary connections. Materials chemistry is a hybrid field that connects chemistry with physics, geology, mathematics, engineering, and the life sciences. Finally, solids have many endearing features if you are a teacher. As my colleague George Lisensky says, “Solids are well behaved: you take them off the shelf, use them, and put them back on the shelf.” Since solid samples often can be reused indefinitely, they are cost effective and they minimize disposal concerns.

Why haven’t solids had a more prominent role in the curriculum? Our committee identified three obstacles to be overcome. One was jargon: much of the language used to describe solids came from other disciplines and needed to be interpreted for a chemistry audience. Second, “curriculum gridlock” had to be addressed: teachers were enthusiastic about including solids in their classes, but skeptical that space could be found in the “close-packed” curriculum. Finally, three-dimensional extended solids were difficult to visualize, and tools were needed to make these structures comprehensible. The central resource developed to overcome these obstacles was a book, published by ACS Books, called Teaching General Chemistry: A Materials Science Companion (3). My coauthors of this volume are Margret Geselbracht, Brian Johnson, George Lisensky, and Bill Robinson. The Companion translates the jargon of materials chemistry into language familiar to chemistry instructors. Curriculum gridlock was addressed by the inclusion of a matrix that allows instructors to map materials chemistry onto their courses. As shown in Figure 1, the left-hand column of the matrix lists topics commonly covered in in-

Vol. 74 No. 9 September 1997 • Journal of Chemical Education

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I C E

Figure 2. The Discovery Slide from the ICE Optical Transform Kit. Diffraction experiments with this slide and other slides that are part of the kit are described in refs 3 and 5.

troductory chemistry courses, and the body of the matrix indicates where to find solid-state examples of those topics in the Companion. Many demonstrations and laboratory experiments are included, as is a complete list of suppliers. Instructors have the flexibility to use the instructional materials in a “cafeteria style”: as much or as little can be used as the instructor desires. The spirit of this approach was summarized in the title of a monograph that was developed to summarize this project, You Do Teach Atoms, Don’t You?— a quotation from George Lisensky that reflects the intent of the project to identify exciting new examples that can be used to communicate core chemical concepts (4). Visualization required various approaches. The first product developed was an Optical Transform Kit, distributed by the Institute for Chemical Education (ICE) and designed to demonstrate how we know the relative positions of atoms in matter. This information is a fundamental part of chemistry and underpins our understanding of the chemical and physical properties of matter (5). Using a pocket laser and 35-mm slides, the optical transform experiment scales the X-ray diffraction experiment upward by a factor of thousands, into the visible spectrum. These slides, an example of which is shown in Figure 2, bear eight different laser-written, photographically reduced arrays, whose feature spacings are thousands of times larger than atomic spacings. In fact, these spacings can be measured easily, using an inexpensive microscope and a plastic ruler.2 They can

be independently measured using the Fraunhofer diffraction experiment (3, 5). However, as we tell our students, there is no corresponding plastic ruler at the atomic level, and we are forced to use diffraction! You can see that passing the laser beam through the eight arrays on the slide produces eight different diffraction patterns. Moreover, if you view the laser beam on the screen through the slide in your hand, you will see the same effect. Finally, if you view a point source of white light, you will note that the light from each diffraction spot has been dispersed into the full visible spectrum, with the red end of the spectrum giving the largest diffraction pattern and the violet end the smallest. More recently, we have made use of an elegant technology developed by Whitesides and co-workers to provide new variations on this experiment (6; Campbell, D. J., et al., J. Chem. Educ., submitted). Specifically, the arrays on the optical transform slide can be transferred to the elastomeric polymer, polydimethylsiloxane, PDMS. If the elastomer is imprinted with a square array, then a square diffraction pattern is seen when the laser beam is passed through it. If the elastomer is now stretched vertically, yielding a rectangular array, the corresponding diffraction pattern is seen to change to a rectangular shape, but with the long direction horizontal. This experiment illustrates the reciprocal relationship between distances separating array features in real space and distances separating diffraction spots in socalled reciprocal space (5). Another variation of this experiment is the use of the “shrink cycle” to create yet smaller feature spacings (Fig. 3). The PDMS elastomer can be compressed in a vise, and its reduced features can be transferred to epoxy. The epoxy, in turn, serves as a template for another PDMS sample, which, when cured, has reproduced the reduced dimensions. The experiment can be repeated, with each cycle causing a further reduction in spacing (6; Campbell, D. J., et al., J. Chem. Educ., submitted). In parallel with the development of the Companion and Optical Transform Kit, we wanted to address the difficulties associated with visualizing extended structures. In two dimensions, it is straightforward to develop arrays based on a building block or unit cell. Trial parallelogram unit cells are easily evaluated by shifting them along each of their edges by the length of the edge and observing whether the structure is replicated. This is applicable to arrays ranging from circles that represent atoms to ducks in an Escher print (3).

PDMS

PDMS

PDMS

Figure 3. The PDMS “shrink cycle.” Features on the surface of a substrate, shown in green (left of figure), are transferred to the PDMS elastomer as it cures (top of figure). The feature spacing is reduced by compression of the PDMS (right of figure) and transferred to an epoxy (bottom of figure), yielding a new substrate, shown in blue, that can be used for a subsequent cycle.

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Journal of Chemical Education • Vol. 74 No. 9 September 1997

Figure 4. Still frames from The Crystal videotape of the Chemistry Animation Project. A unit cell from the face-centered cubic structure has been extracted (top figure) and is replicated first along one dimension (bottom figure) to create a row of unit cells. This row is then replicated to form a single layer of unit cells and finally to form the full three-dimensional structure shown in the top figure. Reproduced with permission.


Figure 5. The structure of sodium chloride, built with the ICE Solid State Model Kit (top panel), and a cleaved salt crystal whose faces correspond to the faces of the cubic unit cell.

To extend these ideas to three dimensions, we received help from Nate Lewis and his co-workers at Cal Tech through the Chemistry Animation Project (7). They developed a visually stunning animation of the face-centered cubic structure. A segment of the animation shows the facecentered cubic (FCC) unit cell, replicating first along one dimension (Fig. 4), then in two dimensions, and finally in the third dimension, dramatizing just what is meant by the term “unit cell”. Early in the project, we recognized that a solid-state model kit was needed. Roald Hoffmann has noted that there is a tactile component that greatly helps in understanding a three-dimensional structure. Development of such an instructional tool, the most ambitious part of the project, was led by Ludwig Mayer and George Lisensky in collaboration with John and Betty Moore and their co-workers at ICE. The kit took nearly two years to develop but it now permits the facile construction of nearly 100 structures, each typically in the span of a few minutes (8). The kit’s effectiveness depends on the fact that it is designed so that there are no degrees of freedom: templates, rods, and spheres in specific radius ratios assure the correct relative positions of the atoms comprising the structures (3). One objective of this project was to connect these extended structures with the properties of the materials they represent. Thus, students can take samples of the rock salt

z=0, 1

1 8 corners X 8 1 6 faces X 2 ---------------4 Cl- ions

z=1/2

1 12 edges X 4 1 center X 1 ---------------4 Na+ ions

Figure 6. A layer sequence for the rock salt structure, showing the correspondence between fractions of atoms contained within the unit cell at different elevations, z, from the base of the unit cell (z = 0) to the top of the unit cell (z = 1) and the empirical formula.

used in water softeners and cleave them by striking them with spatulas. The exposed faces correspond to faces of the cubic unit cell that is easily constructed with the model kit (Fig. 5). We also needed to provide teachers and students with a way to record these structures and to connect them with their empirical formula. Bill Robinson and Frances Galasso acquainted us with a mechanism for doing this using layer sequences, in which planes parallel to the base of the unit cell and passing through the centers of atoms contributing to the contents of the unit cell are recorded. Students quickly become adept at identifying the fraction of an atom lying within the unit cell—an eighth, quarter, half, or all of it—by determining whether the atom’s center lies at a corner, edge, face, or inside the unit cell, respectively (Fig. 6). A compelling way to represent these fractions was devised by Brock Spencer and George Lisensky: an orange, representing a whole atom, is sliced into halves, then quarters, then eighths; and the eight eighths are combined to show a complete atom within the unit cell (Fig. 7). A film clip depicting this analogy is available on a CD-ROM developed by George Lisensky, which serves as a kind of “Companion to the Companion”, presenting nearly 100 animations and film clips based on the book (9). (See also page 1143 of this issue.) Extended structures present eye-opening counterparts to traditional molecular examples. For example, the holes formed by chloride ions and occupied by sodium ions in the rock salt structure feature the same octahedral geometry that we know is adopted by molecules like sulfur hexafluoride. Seeing these complementary forms of the octahedron makes a compelling case to our students that Nature uses this geometry in a variety of ways. Two additional examples demonstrate the breadth of this approach of connecting extended structures with their properties. Diamond is well known for setting the standard for hardness. Inexpensive diamond-tipped scribes are used by our students to scratch glass, and the model kit permits them to explore the origin of diamond’s hardness by visualizing its structure and bonding. Graphite provides a wonderful introduction to layered solids and to electrical conductivity (Fig. 8). Students can draw electrically conducting lines with a pure graphite pencil. Measuring the resistivity along the line lets them discover that resistance increases with length (series resistance) and decreases as the line is widened (parallel resistance). You can make an open circuit by “cutting” the line with an eraser (10)! Electrons, the “glue” that holds atoms together, are well represented in the instructional materials through a variety of electrical and magnetic effects based on such materials as ferrofluids, semiconductors, and high-temperature superconductors. Synthetic approaches, ranging from the traditional “heat and beat” method to the enhanced control of material properties by sol–gel and chemical vapor deposition methods, are included as well. We benefited from the considerable expertise of Martha Greenblatt, Tom Kuech, Joel Miller, Don Murphy, and Stan Whittingham in these efforts. Another objective was to illustrate how physical properties can be chemically tuned. Periodic properties are introduced by connecting structure, composition, and spectroscopy through light-emitting diodes, LEDs. In a simple localized bond picture, we define band gap energy as the energy it takes to excite electrons from bonds, allowing the electrons to be mobile and carry electricity in the solid (3). Group 14 elements with the diamond structure provide a panoramic trend in electrical conductivity. Carbon atoms


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Chemical Education Today Figure 7. Still frames from the Primitive Cubic movie on the Solid State Resources CD-ROM. An atom is represented by an orange, and the film clip demonstrates how each corner atom contributes 1/8 of its volume to the unit cell, making a total of one atom for the contents of the unit cell. Reproduced with permission.

are small and close together. They hold their valence electrons tightly, corresponding to a high band gap energy and poor electrical conductivity. With silicon and germanium, the atoms are bigger and farther apart, and they hold their bonding electrons more loosely. This is reflected in smaller band gap energies, a larger concentration of mobile electrons, and semiconducting behavior. With isostructural tin, the yet larger atoms and interatomic spacings result in such a large concentration of mobile electrons that metallic behavior obtains. We can extend these ideas across the periodic table: if half the atoms of Ge are replaced by Ga, with one fewer valence electron, then replacing the other half of the atoms with As leads to GaAs, which is isoelectronic with Ge and has the related zinc blende structure. Likewise, Zn and Se with two-electron deficits and surfeits of valence electrons, respectively, relative to Ge, combine to make ZnSe, another solid that is isoelectronic with Ge. These structure–composition relationships have a spectroscopic connection, as well: in LEDs, we can excite electrons out of bonds with a battery. When they return to restore the bonds, they release roughly the band gap energy, which can be in the form of heat or light (i.e., photons having the band gap energy). Tunability can be illustrated with solid solutions. Because P and As are chemically similar and of similar size, they can be combined with Ga in arbitrary ratios to create GaPxAs1{x substitutional solid solutions. This compositional flexibility tunes the average distance between atoms, the

Figure 8. The structure of graphite, built with the ICE Solid State Model Kit (lefthand panel), and a measurement of electrical resistance from a line drawn with a pure graphite pencil (bottom panel). (A standard no. 2 pencil contains a considerable quantity of nonconducting binder material that makes it unsuitable for this experiment.)

band gap energy, and hence the color of light emitted. In a sense this tunability is akin to having countless numbers of elements between P and As in the periodic table. Our students use LEDs to see that the color can be varied continuously from red for the most As-rich compositions, through orange and yellow, to green for pure GaP. This provides the backdrop for the current highly competitive technical race to obtain blue light from LEDs and diode lasers. Some of the technological implications of this “blue technology” are CDs and CD-ROMs that hold nearly four times as much information and new technologies for display devices (11). If we ask what element might be combined with Ga in a zinc-blende-like structure to make a blue LED, our students can see that there is yet more real-estate in the periodic table (Fig. 9); and that by combining Ga with N to make GaN, blue light might be obtained. It is empowering for our students to make this extrapolation and to learn that this has, in fact, been a successful strategy. These blue LEDs are now available at modest cost, and their construction employs Ga-In nitride and Al-Ga nitride solid solutions (12, 13). Let me ask you to predict what will happen when these blue LEDs are dunked in liquid nitrogen. Using the simple localized bonding picture I have described, will the band gap energy increase or decrease? Assuming the spectral shift tracks the band gap energy, will the corresponding color emitted by the LED move toward the violet or toward the red part of the visible spectrum? Make a prediction and discuss it with a colleague. [This is an example of a so-called “ConcepTest”, in which students are asked to convince their neighbors in the classroom of the correct answers; see below.] You can see that the color shifts toward the violet (Fig. 10), consistent with the idea that the reduction in internuclear distance at 77 K causes the electrons to be held more tightly, increasing the band gap energy and causing the emitted light to shift to higher energy (14). Direct measurement of the shift using an emission spectrometer shows that the emission band blue shifts upon cooling (Fig. 10). One other experiment I would like to share with you is an illustration of how atomic-scale imaging works, based on a small refrigerator magnet whose edge has been scored for easy separation (Fig. 11) (see the JCE Classroom Activity, inserted following page 1032 of this issue). The edge represents our probe tip, and the remainder of the refrigerator magnet is the sample to be imaged by magnetic forces. If you drag the probe tip horizontally and vertically along the unprinted surface of the magnet (Fig. 12), which of the diagrams describes what you feel: choice A, a uniform magnetic

Al

N

Blue

P

Green

Ga Ge As In

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Red

Figure 9. Portion of the periodic table, showing the trend in LED colors with composition for solids derived from Ga and group 15 elements.

Chemical Education Today field? choice B, a magnetic field whose direction alternates in stripes? or choice C, a magnetic field whose direction alternates in a checkerboard pattern (Fig. 13)? Choice B is correct. If you imagine terminating the tip in a small number of atoms and scanning in atomic-scale increments, this is the kind of methodology used in atomic force microscopy that leads to atomic-scale imaging (15). My co-worker, Dean Campbell, has used a LEGO set to construct a kind of “atomic force macroscope” based on the refrigerator magnet experiment. A probe tip is fashioned by clamping one end of a rigid rectangular plastic LEGO part, making it a cantilever, and gluing a small strong magnet to the underside of its other end. A mirror is placed atop the probe tip, and a pocket laser beam is bounced off of the mirror onto a wall. Using the LEGO set and accompanying motor, the refrigerator magnet can then be moved back and forth, just beneath the probe tip, so that as the tip is alternately attracted to and repelled by the refrigerator magnet, the laser beam position will oscillate on the wall (Fig. 14). My request of you to discuss the blue LED and refrigerator magnet experiments with a colleague illustrate the ConcepTest. Now let me segue into some pedagogical issues related to these instructional materials (2, 4, 16). ConcepTests are emblematic of the cooperative learning methods being used in many of our classes (17). For an instructor, ConcepTests provide feedback, in real time, of how well the class understands the material presented. A website for sharing many of these kinds of questions for inand out-of-class use has been developed, and I invite you to contribute questions to the site (16). Evidence is accumulating that cooperative learning methods—including ConcepTests, small study groups, and an absolute grade scale—are helping to make our classes more user-friendly and effective (2, 17). An absolute grade scale, in particular, encourages students to assist one another without concern that this will jeopardize their grade. As these changes occur, I feel that we are making real progress in enhancing the development of critical thinking skills and in furthering equity, the successful participation of all segments of our student population in our classes. As chemistry instructors, we can benefit from cooperative learning within our own community. For example, among the extraordinary tools now available to us is the World Wide Web. We can share essentially every aspect of our courses—including syllabi, class notes, problem sets, and examinations—almost in real time. This semester, for example, my entire inorganic chemistry course is on the web (18). Another remarkable technological advance that can make our classrooms more intimate is the digital camera. This past semester, we took each student’s picture at the beginning of the class, affixed their first name or nickname, and gave everyone in the class a copy. This enabled my students, my TA, and me to get to know one another much more rapidly than in years past. You can meet my students by visiting my web site. Moreover, if you’ve ever had a yearning to be in pictures yourself, we have new photo opportunities. An example of such a “photo op” is to place your photo into an array, as I did for my first in-class essay exam last semester (Fig. 15). The question was simply to identify and justify the choice of a valid unit cell and then to determine how many of my heads it contained! What has this project taught us about revitalizing the curriculum? First, our experiences with solids have demonstrated that there are many stimulating new ways to teach core chemical principles, grounded, in many cases, in cutting-edge research. Second, if this is to be an ongoing effort, curriculum initiatives can benefit greatly from the ac-

Figure 10. A color shift from blue to violet is observed when a commercial nitride-based LED is cooled by immersion in liquid nitrogen (left-hand panel). Light from two clusters of these LEDs is scattered off a projection screen for ease of viewing in a lecture hall; the LED cluster on the right has just been dunked in liquid nitrogen. The spectral change upon cooling corresponds to a substantial blue shift in the emission spectrum for the device (righthand panel).

tive participation of our community of teacher–scholars. How do we encourage colleagues to participate in the continuous development of new content and pedagogical approaches? Our culture is rapidly changing to support such efforts throughout our various stages of professional development. At the graduate level, for example, many of our students who have made original contributions to chemical education now include thesis chapters on their educational initiatives along with the traditional research chapters. During job interviews, increasingly we are asking candidates about both their teaching aspirations and their research aspirations. And the “reward system” of higher education that is associated with institutions and extramural funding sources is changing to recognize the importance of sustained contributions to both teaching and research. As Roald Hoffmann has noted, there is “…growing respect for teaching in the community of chemistry at large” (19). It has been said that this is the best time in history to do chemistry. I believe that it is also the best time in history to communicate chemistry. As I learn about all of the exciting developments occurring in hundreds of institutions across our country, I cannot help but feel that we are well on our way to having a teaching enterprise whose vitality is commensurate with that of our research enterprise. The challenge for all of us who teach is to keep raising the bar, just as we do in research. It is our collective responsibility to ensure that our students will always have courses that engage them, prepare them, and inspire them. I would like to conclude by acknowledging the many individuals and organizations contributing to this project. Our committee received considerable support from the American Chemical Society, the National Science Foundation (DUE, DMR, MRSEC), the Camille and Henry Dreyfus Foundation, the Dow Chemical Company Foundation, the UW-Madison Outreach Program, and ICE. Dozens of individuals from across the country volunteered their time to field test the materials. Thanks are due the many colleagues and students at UW-Madison, who helped implement and critique early versions of the products developed through this project. I am especially grateful to George Lisensky for his assistance in guiding the project; and to


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A National Science Foundation Materials Research Science and Engineering Center for Nanostructured Materials and Interfaces

http://mrsec.wisc.edu Developed in collaboration with the Institute for Chemical Education and the Magnetic Microscopy Center University of Minnesota http://www.physics.umn.edu/groups/mmc/

http://mrsec.wisc.edu

University of Wisconsin - Madison

Figure 11. A refrigerator magnet whose edge has been scored for ease of separation from the remainder of the magnet. The right-hand edge piece becomes the probe tip for an experiment in imaging.

Sample



Pull Probe Strip

Probe Pull Probe Strip

eral reviewers are thanked for their help with this presentation and article. I am grateful to Glenn Crosby, Bassam Shakhashiri, and Ed Solomon for their enthusiastic support of this project, particularly in its early stages. Portions of this talk are based on material in refs 2 and 3. Notes

Figure 12. Directions in which the probe tip is pulled across the back side of the refrigerator magnet (see Fig. 11).

(A)

(C)

(B) North

South

Figure 13. ConcepTest based on the refrigerator magnet experiment of Figs. 11 and 12: Which of the three arrangements of magnetic field shown—A, B, or C—is consistent with the experimental observation?

my past and present research group members. Finally, I am very fortunate that my family could be present at the presentation of this address. I want to thank my wife, Susan Trebach, our parents, and our children, Joshua and Margot, for their encouragement and support. I invite readers to send comments to me at [email protected]. Thanks for listening. Acknowledgments I would like to thank the Union Carbide Corporation for their generous sponsorship of this award. Cammy Abernathy, Herbert Beall, Dean Campbell, Thomas Kuech, Clark Landis, Julie Lorenz, Joel Olson, Donald Neu, Kathleen Meeker, Susan Trebach, George Lisensky, and sev-

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Figure 14. A LEGO set, accompanying motor, and the refrigerator magnet experiment of Figs. 11–13 can be used to construct an “atomic force macroscope,” as described in the text.

1. The Ad Hoc Committee for Solid-State Instructional Materials: Aaron Bertrand, Abraham Clearfield, Denice Denton, John Droske, Arthur Ellis (Chair), Paul Gaus, Margret Geselbracht, Martha Greenblatt, Roald Hoffmann, Allan Jacobson, Brian Johnson, David Johnson, Edward Kostiner, Nathan Lewis, George Lisensky, Thomas Mallouk, Robert McCarley, Ludwig Mayer, Joel Miller, Donald Murphy, Donald Neu, William Robinson, Don Showalter, Duward Shriver, Albert Thompson, Jr., Ray Turner, Stanley Whittingham, Gary Wnek, Aaron Wold. 2. For example, a 30× Micronta hand-held microscope from Radio Shack works well.

Literature Cited 1. Opportunities in Chemistry; National Academy: Washington, DC, 1985; Pimentel, G. C.; Coonrod, J. A. Opportunities in Chemistry Today and Tomorrow; National Academy: Washington, DC, 1987. 2. Ellis, A. B. Chemtech 1995, 25, 15; Beall, H. J. Chem. Educ. 1996, 73, 756. 3. Ellis, A. B.; Geselbracht, M. J.; Johnson, B. J.; Lisensky, G. C.; Robinson, W. R. Teaching General Chemistry: A Materials Science Companion; ACS Books: Washington, DC, 1993. 4. Lyons, L.; Millar, S. B. You Do Teach Atoms, Don’t You? A Case Study in Breaking Science Curriculum Gridlock; LEAD Center, Univ. of Wisconsin-Madison, 1995; http://www.cae.wisc.edu/~lead/. 5. Lisensky, G. C.; Neu, D. R.; Ellis, A. B. Institute for Chemical Education Optical Transform Kit, 2nd ed.; 1994; http:// jchemed.chem.wisc.edu/ice; Lisensky, G. C.; Kelly, T. F.; Neu, D. R.; Ellis, A. B. J. Chem. Educ. 1991, 68, 91; Ellis, A. B.; Geselbracht, M. J.; Johnson, B. J.; Lisensky, G. C.; Robinson, W. R. Teaching General Chemistry: A Materials Science Companion; ACS Books: Washington, DC, 1993; Chapter 4. 6. Xia, Y.; Whitesides, G. M.; Langmuir 1997, 13, 2059; Xia, Y.; Kim, E.; Zhao, X.-M.; Rogers, J. A.; Prentiss, M; Whitesides, G. M. Science 1996, 273, 347. 7. Lewis, N. S. Chemistry Animation Project, http://bond.caltech.edu. 8. Mayer, L. A.; Lisensky, G. C. Institute for Chemical Education Solid-State Model Kit , 2nd ed.; 1994; http:// jchemed.chem.wisc.edu/ice. 9. Lisensky, G. C.; Ellis, A. B. Solid State Resources CD-ROM; J. Chem. Educ.:Software 1996, Special Issue 12; http:// www.jchemed.chem.wisc.edu.



Figure 15. Is the indicated parallelogram a valid unit cell? A digital camera can be used to create arrays like the one shown in this figure. Students were asked to identify and justify their choice of a valid unit cell and to determine the number of heads contained therein.

10. Woolf, L. D. The Line of Resistance Kit; Institute for Chemical Education, in press. We thank Larry Woolf and Hal Streckert of General Atomics for bringing this experiment to our attention. See, also, a description of a materials science teaching module: Gulden, T. D.; Norton, K. P.; Streckert, H. H.; Woolf, L. D.; Baron, J. A.; Brammer, S. C.; Ezell, D. L.; Wynn, R. D. J. Chem. Educ. 1997, 74, 785. 11. Normile, D. Science 1997, 275, 1734. 12. Neumayer, D. A.; Ekerdt, J. G. Chem. Mat. 1996, 8, 9. Samples of nitrides used in LEDs typically have the wurtzite structure, which is closely related to the zinc blende structure (3). 13. Digi-Key Model P389-ND (tel. 800-344-4539). The multilayer structure of a blue LED can be viewed at http://www.eurotechnology.com/bluelaserbook.html. 14. Assumptions associated with this prediction are given in Ellis, A. B.; Geselbracht, M. J.; Johnson, B. J.; Lisensky, G. C.; Robinson, W. R. Teaching General Chemistry: A Materials Science Companion; ACS Books: Washington, DC, 1993; Chapter 7, using the delocalized bonding description involving energy bands. 15. See http://mrsec.wisc.edu and http://www.physics.umn.edu/ groups/mmc/. We are grateful to Dan Dahlberg of the Magnetic Microscopy Center, University of Minnesota, for bringing this experiment to our attention. 16. The Chemistry ConcepTests website: http://www.chem.wisc.edu/ ~concept/. See, also, Mazur, E. Peer Instruction. A User’s Manual; Prentice-Hall: Upper Saddle River, NJ, 1997. 17. See, for example, Robinson, W. R. J. Chem. Educ. 1997, 74, 622; Nurrenbern, S. C.; Robinson, W. R. Ibid., 623 and references therein. 18. See http://www.chem.wisc.edu/~ellis511/. 19. Hoffmann, R. J. Chem. Educ. 1996, 73, A202.


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Elements of Curriculum Reform: Putting Solids in the Foundation

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