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
