The Energies of Molecules The internal energies of atoms and molecules determine both their physical and chemical properties, and, therefore, knowledge of these energies is essential to the understanding of the very nature of matter. However, this knowledge is gained through abstract theoretical considerations and difficult (and often tedious) mathematical manipulations. Teachers introducing these concepts to students are often faced with either simplifying the exercises and thereby misreoresentine the true nature ofthe work or overwhelmingtheir tory presentations without sacrificing their accuracy and utility; one of the more recent solutions to their problem has been the use of the computer to handle the tedious and repetitive work, thus freeing the students to concentrate on the theoretical aspects of the manipulations. Three articles in this issue cover some aspect of internal energy and its effect on atomic and molecular properties; two of them utilize the computer to allow introduction of these ideas to undergraduates. Potential energy curves for diatomic molecules can he calculated readilv hv undergraduates usinr Morse functions: deduan, and Martinez (page 91jdescribe this method and how they use it in conjunction with a microcomputer program to have their students calculate the potential energy curves for Ie. The internal energy of a molecule is useful in understanding its chemical reactions. Perez and Quereda (page 121) present an exercise for their undergraduate physical chemistry laboratory that examines the statistical and microscopic description of a chemical reaction, utilizing a computer program. Another effect of the energy of an atom is on its chemical properties such as oxidation state. McKelvey (page 112) points out that anomolous properties of certain heavy elements can he explained by including relativistic effects in the solution of the wave eauation. Startine with the for presentation to undergraduates.
Introducing Concepts in Physical Chemistry The teacher of introductory physical chemistry has the identical problem described above: how to simplify the in-
90
Journal of Chemical Education
troduction of certain difficult concepts so that students can maso their essentials without misreoresentin~their nature. thermodynamics is the same as in classical thermodynamics without oresentine" conceots too abstruse for a first course. He offers an alternative proof that avoids these complications hut is still primarily deductive. Teachers wishing to review earlier articles on introducing various thermodynamic concepts to students will find an annotated bibliography in this month's Something New from the Past feature (page 105).
Representing Three-Dimensional Molecules in Two Dimensions Organic chemists, in particular, deal with complex, threedimensional molecules; however, their primary modes of have been developed for repesenting this "three-dimensionaless" in ways that are unambiguous and familiar to all. Teaching these two-dimensional systems of representation to students who are still struggling with envisioning the three-dimensional structures can he a frustrating exercise fur student and teacher alike. Hargittai (page 94) in this month's cover article shows how he enlivens his class presentation of projection drawings,of rotational isomers through the use of analogies with well-known drawings by Degas. The computer screen, while still two-dimensional, can, through sophisticated graphics programs, be used to represent three-dimensional molecules far more realistically than a quick drawing on blackboard or paper. Two such programs are described in this month's Computer Series feature (page 96). Kaleher's program includes considerations of perspective and the shading and overlap of the spheres which represent the atoms. I t will also produce a 3-D stereo pair. Hull has adapted a 3-D graphics routine, originally designed for use in games development, to produce animated displays of molecular line drawings. A representational system which is not used accurately hy everyone can lead to more confusion than no system at all. A recurring prohlem of this nature is pointed out by Fulop, Bernath, Szabo, and Dombi (page 95) in their article "Correct Representation of Conformational Equilibria".
