The Concept of Isotopy The discipline of chemistry, like all sciences, has grown by fits and starts: periods of rapid accummulation of new data which have produced a chaos that threatened to pull apart its theoretical fiber have been followed by periods of great leaps in theoretical insight which subdued the chaos and found a place for i t in the orthodoxy of the time, often not without great reshaping of the orthodoxy itself. This has no better illustration than the period around the turn of the century when the investigation of radioactivity was producing so much excitine new data and so manv new "elements" that the whole concept of periodicity seemed in danger of sinking, literally, under these elements' weight. The orohlem of what to do with elements with slightly different atbmic weights but identical chemical properties was first solved by denial: improper weight determinations must he leading to this anomaly. As methods improved and data accumulsted, however, it became clearer that these new elements would not go away through wishful thinkine. and the conceot of isotoov sained urecedence and was confirmed, bringing order back tb the pekodic table and opening new areas for scientific investigation. Kauffman (page 3) in his article "The Atomic Weight of Lead of Radioactive Origin: A Confirmation of the Concept of Isotopy and the Group Displacement Laws" examines in devth this oeriod and tells of the inception of the concept of isoiopy, its-definitive statement by ~ o d d yand , its confiimation throueh the work of Richards and others. The interweaving of the work and ideas of a wide number of people with different aooroaches and nationalities to produce and refine this concept, which is one of the corne&ones of modern theory, is an interesting story, not only of the development of an idea but of the workings of science itself.
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Since the molecule is the basic discrete particle produced when elements combine. chemical investieations are centered around finding out how macroscopic obiervations relate to occurences at the molecular level. That. to the chemist, these occurences are what is "really" happening is evidenced in everything from the way we write equations for reactions to the basic premises of most of our theories. Several articles in this issue, althowh unrelated at first dance, are all concerned with examining what is happening a t the molecular leveleither when molecules interact with each other or some form of energy or when they are isolated and are in equilibrium with their own kind. Our understanding of the exact nature of what happens when two molecules make contact and react (or fail to react) is still being refined; however, great strides have been made in the last decade through modern experimental techniques. Smith (page 9) points out that very little of these new refinements have been incorporated into the undergraduate 2
Journal of Chemical Education
curriculum because of the complexity of the theory and the calculations. He proposes a modification to the simple collision theory-which has so many defects that its pedagogic value is nil-and shows that this "New Collision Theory for Biomolecular Reactions" compares with the more rigorous quasiclassical calculations well enough to be useful as a teaching tool at the undergraduate level. Molecules not only react with each other but also with various forms of energy that impinge on them: sometimes by disintegrating into new forms, sometimes by absorbing electromagnetic energy and possibly radiating it at another wavelength characteristic of a particular kind of molecule, and sometimes by using the energyta initiate reactions with other molecules. The absorption of infrared energy by molecules in waveleneths characteristic of the soecific comoound has lone been use; to identify unknown sub8tances. he traditional i n h e d suectroscovv methods involve measurement of the transmitted energy; however Nogar and Fisher (page 15) describe "Thermal Spectroscopy," a new method which measures, instead, the energy actually absorbed by the molecules. They outline the various forms of the method and discuss its auplications and advantages. The interaction of light with molecules can produce the results discussed above (absorption of the energy), but it can also cause the absorbing molecule to disintegrate into new substances. One particularly annoying example of the latter is the effect of light upon the flavor of beer. In "Photochemistry and Beer" Vogler and Kunkely (page 25) show why brown bottles are necessary to filter out the wavelength of radiation responsible for the disintegration of the particular molecule which gives beer its typical flavor. In a related narrative of science in the service of humankind, a detailed description of a long, involved series of molecular reactions which have generated more interest throughout history than just about any others is given by Oliver, Kemoton. and Conner (naee 49) in their Chem I Suoolemen( "The Production b;f Ethadol from Grain." T h G d e scribe the traditional industrial anoroaches as well as some .. new investigations engendered by the interest in "gasohol" as an alternative fuel. erties of groups of molecules that are not undergoing any modifications whatsoever. One such important property is the distribution of molecular velocities in a gas, which Maxwell derived in the latter half of the Nineteenth Century. Dunbar (page 22) points out that the original derivation published by Maxwell, which is the basis of the one appearing in most physical chemistry texts, was later regarded as inadequate hy Maxwell himself and that he spent a great deal of time developing more secure proofs. Dunbar shows the problem with the original derivation and goes on to present a more satisfactory method for use in introducing the concept to students.
