JOURNRL OF
Chemical Education: Software Abstracts for Volume 2 D, Number 1 A Window on the Solid State Part I: Structures of Metals Pafl 11: Unit Cells of Metals William R. Robinson
Purdue University West Lafayene, IN 47907-1393 "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 closepacked 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, efficiencyof packing, and how to draw the structures using two-dimensional representations. The pseudoanimation used is particularly effectivein distinguishing between hexaeonal close-~ackineand cubic close-~ackine. "Part 11: &it Cells df ~ e t a discusses k hodto useaunit cell to describe a two-dimensional structure. then extends the concept to metals using the four basic &it cells of the metals: the simple cubic, body-centered cubic, face-centered cubic, and hexagonal cells. The relationships between radii of the metal atoms in the cubic structures and
Comparson of layers in nexaqona cose pacaea am c-oc cosepackeo struct~resfrom A Vv noow on tnc So n Stalp Both the lecture and tutorial versions are intended as supplements to an introductory presentation, either at the general chemistry level or at the first introduction of the structures of metals at the undermaduate level. These ~ r o grams emphasize the qualitative-and geometric aspeds of the structures presented. Although no numerical calculations are requested in these programs, students will be well prepared to tackle quantitative exercises by the information presented. This program was written while the author was on sabbatical leave as a 1992-93 SERAPHIM Fellow with Project SERAPHIM at the University of Wisconsin-Madison. The support of Purdue University and the National Science Foundation through grant # MDR-9154099is greatly appreciated.
How a Photon Is Created or Absorbed Giles Henderson
Eastern Illinois University Charleston, lL61920 Robert C. Rittenhouse Walla Walla College College Place, WA 99324 John C. Wright Jon L. Holmes
Illustration showing the number of atoms occupying a body-centered cubic unit cell from "A Window on the Solid State". the cell dimensions are developed. Students are also introduced to counting the number of atoms in a unit cell. Pseudo-animation is particularly effective in illustrating the fractions of atoms that lie in the various unit cells. Two versions of each part are provided. One is a student tutorial that allows a student to workthrough the material at herihis own pace. Thisversionrequires students to identify or predict structural features and includes pop-up boxes that confirm or correct choices. Hot words are used to link ideas and provide definitions. The other version is designed to be used in lecture demonstration; it contains all graphics and summary statements from the tutorial program, but is less interactive. 300
Journal of Chemical Education
University of Wisconsin-Madison Madison. WI 53706 "How a Photon Is Created or Absorbed" is an electronic version of a paper by the same title published in this Journal in 1979 ( I ) . This electronicversion operates under Microsofi Windows; a Macintosh version is also available (2) Only minor revisions have been made in the text, but the electronic medium allows the authors to provide interactive graphics and animations that illustrate the points being made much more effectively than could be done in the print medium. Quantum transitions are typically represented by vertical arrows connecting energy levels, and the emphasis is on the requirement that the energy of the photon equal the difference between the two energies represented by two horizontal lines. It is natural for students t o wonder what
A series of framestaken from the animation ofthe 2p to 1s transition in a hydrogen atom that constitutes Figure 7 of "How a Photon Is
Created or Absorbed".
actually happens when a photon is created or absorbed by such a transition, but such questions are seldom addressed. This paper provides a visually interesting and quite striking model of the mechanism of the process. It does so by means of spreadsheet calculations and graphic displays of dynamic quantum trajectories for transitions involving a rigid rotor and a harmonic oscillator, and animations of the behavior of electron density in a hydrogen atom undergoing the allowed 2p to 1s transition and the forbidden 2s to 1s transition. These replace static figures that appeared in the original paper. This paper is written in Microsoft Word for Windows. Charts *om spreadsheets written in Microsoft Excel have been embedded in the Word document to display some of the figures (rigid rotor and harmonic oscillator). The animations of electronic transitions for the hydrogen atom are also embedded in the Word document using Asymetrix MediaBlitz. Word and Excel are required in order to read the paper. In addition to its pedagogical value relative to enhanced understanding of quantum transitions, this paper pioneers a format that we expect will become more common in the future, namely an electronic document that makes use of graphic and calculation abilities of computers to enable better understanding of an otherwise arcane topic.
Volume 71 Number 4 April 1994
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