Modification to Flow Chart to Determine Point Groups
letters Chemistry in the Comics
To the Editor: Henry A. Carter's excellent series, "Chemistry in the Comics" [1988,65,1029; 1989,66,1181,unfortunately fails to mention that the treatment of science in comic books, although engrossing and exciting to students, sometimes contains errors, both major and minor. For example, in Figure 12 11988, 65, 10341, concerning Humphry Davy's experiments on the physiological effects of nitrous oxide, the Royal Institution is referred to as the "Royal Institute". In Figure 4 [1989, 66, 1201 Robert Boyle, the seventh son of the First Earl of Cork, is called an Englishman, instead of being identified as Irish. Such errors, however, need not preclude the use of comic books in science courses. Believing that if one is handed a lemon, one should make lemonade, I often assipn my students the task of discovennfi ermm in textbooksand-other materials. This technique, if applied to comic books, will motivate students to consult reference books and pursue topics to a greater depth than is provided in the typical comic book treatment.. Also, although comic books sometimes provide warnings about dangerous practices, as shown i n ~ i ~ u16 r e[1989, 66, 1241, earlier, before these litigious times, this was not always the case. As a teenager,? duplicated the Joker's preparation of nitrous oxide (he used the "laughing gas" to incapacitate Batman and Robin) by heating ammonium nitrate. It was only when I later read the newspaper account of the disastrous exnlosion of the S. S. Grandcamn on April 16,1947, in the harbor ofTexas City, resulting in'570 deaths. that I realized the notential daneer inherent in the thermal decomposition of ammonium nitrate. Incidentally, in Carter's second article Figures 2, 5, 6, and 8 do not correspond to the captions.
To the Editor. Recently. your Journal published (1)a flow chart for " " d~trrmimngthe symmetry pomt g~oupsin the HermannMauein notatlon that we have found particularlvu~efulfor a course on crystal chemistry where misleading presentations of both the Hermann-Maugin and the Schoenflies notations should be avoided. This has been discussed in your Journal along with the associated conceptual difficulties (2,3). In using the flow chart diagram cited above we have found a drawback in the most symmetric cubic system. Specifically, ~fwe arc intcrcsted in finding thc point group for an octiihedral molecule. sav SF.. we never reach the m3m group. Instead, we aiwais getthe 432 point group, which, although it represents octahedral symmetry, is not t h e proper group for t h e SF6 molecule.Therefore, we propose the modification shown in the figure.
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We have kept the classification criteria based on the existence of mirror planes normal to the four-fold axes, although the existence of an inversion center could be used as a criterion as well lgnasl Casas and Juan J. Perez
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George 6. Kauffman
California State University, Fresno Fresno. CA 93740
Dpt. d'Enginyeria Quimica E.T.S. d'Enginyers Industrials, UPC Avd. Diagonal, 647 08028 Barcelona, Spain Literature Cited 1. BrenemanO.L . J Chem. Educ 1981.61,211. 2. Ladd M. F.C . J Chem. Educ. 1880.67.636. 3. SharmaB. D.J ChemEduc. 1982.59,567; 1989.60.462
Volume 69 Number 1 January 1992
83
