Information • Textbooks • Media • Resources edited by
Journal of Chemical Education Software
Jon L. Holmes Nancy S. Gettys University of Wisconsin–Madison Madison, WI 53706
Two Programs for Windows: Abstract of Volume 5D, Number 2 1. A Window on the Solid State: Part I: Structures of Metals; Part II: Unit Cells of Metals; Part III: Structures of Ionic Solids; Part IV: Unit Cells of Ionic Solids William R. Robinson and Joan F. Tejchma Department of Chemistry, Purdue University, West Lafayette, IN 47907-1393 A Window on the Solid State helps students understand and instructors present the structural features of solids. Parts I and II were published previously by JCE Software (1) and Macintosh versions of Parts I and II are also available (2). Parts I and II have been updated to include improvements in art and minor changes in logic. Parts III and IV expand the collection to include the structures of simple ionic solids using the visual effects available in an interactive computer medium. The package provides a tour of the structures commonly used to introduce features of the solid state. Part I: Structures of Metals introduces the four basic structural types found in metals: the hexagonal closest-packed structure, the cubic closest-packed structure, the body-centered cubic structure, and the simple cubic structure. These structures are introduced as stacks of close-packed planes of metal atoms in the hexagonal and cubic closest-packed structures, and stacks of less efficiently packed planes in the other two structures. In addition, Part I also introduces Laves’s principle, coordination number, stacking of planes, efficiency of packing, and how to draw the structures using two-dimensional representations. The pseudo-animation used is particularly effective in distinguishing between hexagonal closepacking and cubic close-packing. Part II: Unit Cells of Metals addresses the use of a unit cell to describe a two-dimensional structure, then extends the concept to describing the structures of metals using the four basic unit cells of the metals: the simple cubic, body-centered cubic, face-centered cubic, and hexagonal cells. The relationships between the radii of metal atoms in the cubic structures and the cell dimensions are developed. Students are also introduced to counting the number of atoms in a unit cell. The pseudo-animation that illustrates the fractions of atoms that lie in the various unit cells is outstanding. Part III: Structures of Ionic Solids describes simple ionic structures in terms of the packing of positive ions in holes in arrays of negative ions. In the course of the presentation, the features common to the packing of ions in binary ionic solids are described. Animation is used to introduce the radius ratio rule (smaller ions “rattle” in larger holes and larger ions do not fit into smaller holes). Tetrahedral and octahedral holes are highlighted in closest-packed arrays of anions. Then the coordinating anions are isolated and rotated to show their geometry. Cubic holes appear in simple cubic arrays of anions. Finally, the CsCl, CaF2, NaCl, TiO2, and cubic ZnS structures are built layer by layer using animation to show alternating layers of anions and cations and discuss the type and fraction of holes occupied.
Screens from Parts III (above) and IV (left) of A Window on the Solid State
Part IV: Unit Cells of Ionic Solids discusses the unit cells of five common ionic structures: the CsCl, CaF2, NaCl, TiO2, and cubic ZnS structures. A pseudo-animation very effectively illustrates the relation of the unit cell to the extended structures described in Part III. The locations of ions of each cell are illustrated with spacefilling and ball-and-stick models. When appropriate, the relationship of alternate unit cells is described. Coordination numbers of cations and anions are highlighted and students are shown how to determine the numbers of ions in a unit cell. Pseudo-animation is particularly effective in illustrating the fractions of atoms that lie in the various unit cells. The relationships between the ionic radii and cell dimensions are developed. All four parts of A Window on the Solid State can be used by students in individual or group tutorial settings. Students can work through the material at their own pace. Each part requires students to identify or predict structural features and includes pop-up boxes that confirm or correct choices. Hotwords are used to link ideas and provide definitions. Parts I and II also have versions optimized for classroom presentation. Acknowledgments Parts I and II of this program were written while the author was on sabbatical as a 1992-93 SERAPHIM Fellow at The University of Wisconsin–Madison. The support of Purdue University and the National Science Foundation through grant #MDR-9154099 is gratefully appreciated. Literature Cited 1. Robinson, W. R. A Window on the Solid State; J. Chem. Educ. Software 1994, 2D No. 2. 2. Robinson, W. R.; Sari, C. P. A Window on the Solid State for Macintosh; J. Chem. Educ. Software 1994, 6C No. 2.
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Information • Textbooks • Media • Resources
2. Solid State Structures Ludwig A. Mayer San Jose State University, San Jose, CA 95192 Solid State Structures is a collection of image files that allows the user to display, rotate, and examine individually a large collection of 3-D structure models. Previously published as Solid State Structures for MacMolecule (1), the collection is now available for Windows users with PCMolecule2 or PCMolecule2 Lite (2). Created specifically to simulate and complement models constructed using the ICE Solid State Model Kit (3), the structures provide an effective visualization. The collection is divided into three parts: Illustrated Guide Structures, Coordination Geometries, and Complementary Structures. The Illustrated Guide Structures simulate structures presented from each page of the Instruction Manual to Accompany the Solid-State Model Kit and the Illustrated Guide to Accompany the Solid-State Model Kit. The images in the Coordination Geometries correspond to those in the Instruction Manual to Accompany the Solid-State Model Kit, enhancing them by us-
ing techniques that are not possible with the model kit alone. The Complementary Structures emphasize features of selected structures from the Illustrated Guide Structures, again using techniques not possible with the physical structure models.
A tetrahedral hole as displayed in Solid State Structures.
Literature Cited 1 Mayer, L. A. Solid State Structures for MacMolecule; J. Chem. Educ. Software 1994, 6C, No. 1. 2. Myers, E.; Blanco, C.; Hallick, R. B.; Jahnke, J. MacMolecule v 1.7; University of Arizona, Tucson, AZ 85721, PCMolecule2; Molecular Ventures, Inc. 3661 N. Campbell Ave. #604, Tucson, AZ 85719. 3. Mayer, L.; Lisensky, G. C.; Solid State Model Kit, Institute for Chemical Education, University of Wisconsin-Madison, Madison, WI 53706.
Using these JCE Software Programs in the Classroom An understanding of the extended structures of solids is as fundamental to understanding the behavior of matter as is an understanding of the structures of molecules. The bulk of the substances that we interact with every day are solids with extended structures. The presentation of the structural features of solids with extended structures challenges even an experienced instructor. There is no simple way to introduce these concepts. Models are clumsy, and two-dimensional drawings take time to produce and do not always get the job done. One technique that has proved effective involves use of lap-dissolve slides with a mix of photographs of extended models, photographs of unit cell models, and graphics (1). However, such slides are not generally available. A Window on the Solid State provides similar information but in a format that is easy to use. Solid State Structures provides an excellent companion to the ICE Solid-State Model Kit. It can be used quite effectively in lecture presentations because models take no time to build and are easily manipulated. The computer structures are also useful when groups of students are building solid-state models with the kit, because they can be used to verify the correctness of constructed models. In addition, the computerized version has features
that are not available in the kit. Models can be viewed as ball-and-stick as well as space filling, so that atoms within a structure become visible. Sticks can also be used to good advantage to connect nearest neighbors and show coordination numbers and geometries. Literature Cited 1. Bodner, G. M.; Greenbowe, T.; Robinson, W. R. J. Chem. Ed. 1980, 75, 555.
Ordering and Information Journal of Chemical Education Software (often called JCE Software) is a publication of the Journal of Chemical Education. There is an Order Form inserted in this issue that provides prices and other ordering information. If this card is not available or if you need additional information, contact JCE Software, University of Wisconsin-Madison, 1101 University Avenue, Madison, WI 53706-1396; Phone; 608/262-5153 or 1-800/9915534; fax: 608/265-8094; email:
[email protected]. Information about all of our publications (abstracts, descriptions, updates, etc.) is available from JCE Online: http://jchemed.chem.wisc.edu/.
Table 1. Hardware and Software Requirements for Programs in JCE Software Volume 5D, Number 2
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Computer
CPU
RAM
Drives
Free Disk Space
Graphics
System
Other
A Window on the Solid State
Windows compatible
≥ 80386
≥ 8 MB
Hard drive, High-density (1.44 MB) 3.5-in. floppy drive
14 MB
640 × 480 ≥ 256 colors
Windows 3.1x or Windows 95
—
Solid State Structures
Windows compatible
≥ 80386
≥ 8 MB
Hard drive, High-density (1.44 MB) 3.5-in. floppy drive
2 MB
640 × 480 ≥ 256 colors
Windows 3.11 with Win32s or Windows 95
PCMolecule2 or PCMolecule2 Lite
Journal of Chemical Education • Vol. 74 No. 9 September 1997
