Advances in science and technology afford new opportunities for enriching and updating the chemistry curriculum by connecting such developments and their products to core chemical principles. This article illustrates this approach to curriculum modernization using advances in lighting and display technologies with light-emitting diodes (LEDs). As noted in an industry summary, an excellent resource for this topic, LEDs are replacing traditional incandescent sources in many lighting and display technologies for reasons of energy efficiency, safety, and conservation. Their widespread use in vehicle, traffic, display, home, and workplace lighting provides opportunities to directly engage students' interest. The chemistry underpinning LEDs spans many core chemistry curriculum topics, because the semiconductors in the light sources comprise a family of essentially isostructural solids that embrace a variety of periodic trends. Bonding trends exemplified by the solids include electronegativity, atomic radii, bond polarity, isoelectronic principles, and spectroscopic transitions. The solids also provide an acid-base and concentration cell system that complements traditional presentations of aqueous systems. At a more advanced level, the quantum mechanics of spatially confined particles can be presented with this family of solids. This approach to curriculum modernization also affords opportunities to establish interdisciplinary links between chemistry and other scientific and engineering fields.

In general chemistry courses, the majority of the chemical examples are gas mixtures or aqueous solutions. However, the most prevalent state of the chemical materials encountered everyday is solid. Thus the recent emphasis on the teaching of solid-state materials in the general chemistry classroom (1).Any discussion of solid-state chemistry involves a description of structure (2). One of the basic structural themes in the solid state is that of close-packed spheres. Atoms are approximated as hard spheres that arrange themselves in such a manner as to reduce voids. The two close-packed structures, hexagonal closest packed (hcp) and cubic closest packed (ccp), and their derivatives are observed in the noble gases and many metals, and also in alloys and ionic and covalent compounds (3). Interestingly, other close packings are possible if the structures aren't periodic (4, 5).The close packing model is therefore a powerful tool for explaining many solid-state structures. To facilitate learning of the close packing model, many demonstrations of closepacking spheres have been developed (6)(7)(8)(9)(10)(11). Most of the models in the literature are static: spheres or circles are packed and stacked by hand and frozen into the familiar hexagonal lattice. Static models, though visually demonstrating the arrangement of spheres in a hexagonal array, don't explore any of the other possible ways of packing spheres. Students may wonder why the instructor has to intervene to force the coins or balls to assume the right shape. A dynamic model, one that both demonstrates the close packed structure visually and spontaneously assumes this structure, is aesthetically more satisfying.Such a dynamic demonstration was exactly what Bragg and Nye reported in 1947 with the bubble raft model. This model has recently been adapted for overhead projection (1, 12). However, the apparatus involved in making the bubble raft demonstration is complex.

No abstract

No abstract

No abstract