E D I T O R I A L L Y SPEAKING A n art,icle in this issue which should receive carefill and thoughtful reading by all chemist,sis Professor Guggenhrim's "The Mole and Relat,ed Quant,it,ies." In simple unambiguous language it sets fort,h what is probably the primary unifying concept in the modern chrmist!s view of t,he materials with which he deals. Only t,he flimsiest semant,ic arguments can be found with the statement,: "The mole is the amount of substance containing the same number of molecules (or atmns or radicals or i a s or electrons as the case may be) as there are atmns i n twelve grams of carbon-12.'' Teachers of chemistry get their firmest feeling of success when student,^ demonstrate that they know what. "mole" means. When the stmudentcan do this not by writ,ing a dcfinit,ion in so many words hut by using t,he concept, he begins to t,hink as a chemist does. The import,ant recognit,ion comes when the t,erm "mole" stands for a definite number of any particular spccics. Textbooks have long lagged behind the prevailing pat,tern of t,hinking by the best teachers of chemistry on this point. One looks in vain for even t,he use of the word in all but the newest high school text,s. The t,erm is used in most. text,s for the introductory college course, hut usually the student is left only mit,h t,he idca that a "mole" is a "numher of grams. . ." Professor Guggenheim, later in his discussion, gives emphat,ic int,erpretation to his use of t,he word "amount." This is the implication which needs t , he ~ underscored for the neophyte chemist,. Although perhaps unconsciously (as wit,h some t,eachers, alas!), t,he working chemist now thinks in numhers of reacting species rather than in weight,s or even relative weight,^ of matmerialsinvolved. Crrtainly as soon as he anticipates t,he measurement of energy associated with a given reaction he must consider Avogadro's number of events a t t,he at,omic level as a st.andard for reference. A second implication grows out of this number definition. This is the inclusion of the parenthesis in Professor Guggmheim's stakment. Here again, common usage hy working chemist,^ t-ranscends the t,exthook definition by not limit,ing the mole concept to gram-molecular weight. A st,udent who realizes t,hat t.he Faraday represents the charge of a mole of electrons will have a t his disposal t,he key concept to applications ranging from electrolysis to redox tit,mt,ions. Anot,her big advantage is built into this definition
which emphasizes number of spccics: it is a concept, which can grow in significance as a student's chemical knowledge accumulates. It may be expedient to base the first use on the wcight idea, for examplr, in the st,oichiomet,ry which may appear very early in an elementary course. Later it will not he tossed aside nor even strained to encompass more sophisticated theory. We recall once receiving some letters (we keep t,hem in an asbest,os file) castigating us for puhlishing an article which defined a mole as a weight conhining 6.023 X loz3 molecnles and t,hen applird t,hat definition t,o an amount of HKOa, S,or Bi(l\TO&. The point of the art,icle was to emphasize thc advantagr of t,he mole concept in the first introduction of s high school student to stoirhiometry. We admit to the edit,orial sin of laxit,y in not using the h h ~ epencil t,o introduce t,he term "formula weight." Howcver, we doubt that there would be any ambiguity in the mind of a student at, t,hat rarly stage of his first course. I-Ie was being taught to make proper usc of t,he concept to solve stoirhiomet,ric prohlcms hased on a complicated hut balanced equat,ion dcscrihing unfamiliar chemist,ry. We doubt, too, t,hat t,his initial working concept of mole could block the student's later appreciat,ion of what, modern theories of electrolytes or bonding in solid substances could add to hi* earliest recollect,ion (that coefficients in a balanced equation establish the relative numbers of reacting moles). We doubt t,hat a t,eacher would have trouble later in convincing him that a mole of Bi atoms will lose t,hree moles of electrons to form a mole of Bi+++ ions which probably will react in aqueous solution to form a variety of ot,her species whose molar concentration may be calculated if appropriahe equilihrium constants are known, etc. There is an interest,ing cont,rast bet,wecn the modern problem presented by this art,icle and Dr. Ihde's account of the circumstances under which t,he Iiarlsruhe Conference was convened by IiekulB a century ago. Chemistry, still a young science, has moved far in 100 years. Yet t,hen as now, t,he magnificent strength of a unifying concept was the hasis for the advance of chemistry. Then i t was a gradual resolving of chaos; now it is the correlating and conseqnent simplifying of diverse phenomena. Cannizzaro's advocacy of Avogadro's hypothesis was hased on his use of it ". . . to lead my standentsto the conviction which I have reached myself." We doubt if anyt,hinp more important than a unifying concept has heen invcntcd in 100 years of successful chemistry teaching. Volume
38, Number 2, February 7 961
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