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kCc N e w England Association of Chem
Quentin R. Petersen' Simmons C o l l e g e B O S ~ O Massachusetts ~,
021 15
Some Reflections on the Use and Abuse of Molecular Models
A n article in the New Yorker magazine of several years ago (1) titled "A Farewell to String and Sealing Wax" was a profile, done in the typical "New Yorker" fashion, of Dr. Samuel A. Goudsmit, chariman of the physics department a t Brookhaven Laboratories, Editor of Physical Review, and co-discoverer of the phenomenon of electron spin. The passages which drew my particular attention were the following quotation To some teachers an atom is always a ball. I n the winter it's a basketball, in the spring it's a baseball, and the rest of the time it's a. pingpong ball. The atom is no more explained by such images than the idea of Cad is by a picture of an old man with a. long beard sitting on a, cloud.
and a description of one of Goudsmit's lectures . . . h e discussed the pitfdls man ha9 encountered in trying to resolve the most basic puzzles of nature in terms of "wire models and ping pong balls."
A recent letter in Chemical and Engineering News ( 2 ) reflects the same opinions in somewhat less philosophical terms by stating that Painted balls connected by rods are less like real atoms than department store mannequins are like real women.
Having had some success with the visualization of the atom as a ball in both research and teaching, and having at one time during my attempts to make molecular models considered myself quite a ping pong fancier, I was quite naturally concerned. In looking at what history shows to havc been accomplished through the use of "wire models and pong pong balls," I have reassured myself that these artifacts have indeed served and are still serving a very useful, important function which could not be achieved in any other fashion. Based on a lecture delivered to the 30t.h Summer Conference of the New England Associstion of Chemistry Teachers a t Wesleyan University, August, 1968. 'Present address: Department of Chemistry, Monmouth College, Monmouth, Ill. 61462. If, as some contend, the degree to which s worker's contemporaries oppose or ignore his new concepts is a measure of their greatness, Biot's contributions clearly met the test as he tried unsuccessfully to interest other chemists in the phenomenon. Tollowing the presentation of this lecture, Professor 0.T. Benfey (4) pointed out the fascinating fact that Dalton, as early as 1812, had had models mnstrueted for him from pins and spheres! The tetrahedron was not included, however.
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Journal of Chemical Educotion
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Historical Applications of Molecular Models
I n 1808 Malus discovered polar&d light. In this same year Wollaston (3) made the following suggestiou . . .when the number of one set of particles exceeds in the proportion of four to one, a stable equilibrium may again take place if the four particles are situated a t the angles of the four equilateral triangles composing a regular tetrahedron.
He also added a t the end of his communication I t is perhaps too much to hope that the geometrical arrangement of primary particles will ever be perfectly known.
In 1815 Biot observed that a number of naturally occurring organic compounds had the property of rotating the plane of polarization of polarized light. While quartz crystals were known to rotate the plane, Biot found that the organic materials effected this rotaation whether crystalline, liquid, or in solution. It is to his everlasting credit that he interpreted these observations as proving that the rotation of light was due to some property of the individual molecule itself. Pasteur in 1848 found that crystals of sodium ammonium racemate, when prepared in a certain way, had hemihedral facets, some of which were right handed and some of which were left handed. Proceeding by analogy with quartz, he separated the two types of crystals and found that in solution they rotated the plane of polarized light equally, but in opposite directions. This work, of course, was not and could not he fully interpreted until it was examined in terms of the tetrahedral quadrivalency of carbon, and this concept was not then in use. Just when it became available is a little obscure, but it was available well before van't Hoff (see I
