A PROPOSED REARRANGEMENT of the SUBJECT MATTER of ELEMENTARY CHEMISTRY* G. WAKEHAM University of Colorado, Boulder, Colorado
The most important characteristic of chemical action is the strictly quantitative nature of the relations between the substances involved. This feature can hardly be over-emphasized. Students cannot be too eady inducted into the use of the balance-a process the meaning of which they readily g r a s p a n d reasonably accurate balances doubtless constitute the most important item of laboratory equipment. The present writer objects to most of the experiments commonly used to lead up to the law of definite proportions because they involve the manipulation of gases, or a t least a clear concept of the nature of the gaseous phase. This objection applies to the analysis and synthesis of water, the heating of limestone, the calcination of magnesium or some other metal, the use of the reversible reaction of mercury with oxygen, etc. The writer prefers for this purpose some simple reaction between solid (or liquid) elements, such as sulfur and iron. A logical, simple, and convincing deduction of the law of definite proportions, leading up to the atomic theory, can be based upon the gravimetric results of such experiments. Beginning students usually find the law of multiple proportions unintelligible, and it is not necessary to the presentation of atomic theory. The heat effects involved constitute the second most important characteristic of chemical reaction. A touch of the "heuristic" method may well be used here. Throughout the ages, combustion was one of the most important and puzzling of philosophical problems. Stahl's approach to this question was probably the first rational, clearly stated theory in the history of chemistry. Some daring teachers actually lead their classes through the whole phlogiston period, giving them the theory without any warning of its fallacious nature, letting them cany out calcination and reduction experiments to "prove" the theory, and then allowing them to demonstrate its improbability by simple modifications of Lavoisier's crucial work. This is a very effective method of allowing the concept of "gas" to develop in the student's mind. One of the commonest mistakes made by teachers and textbook writers is the easy assumption that the average student already bas a clear notion of what a gas is. Students can memorize gas laws and learn to work-by formulas-gas-law problems without having the slightest idea of what they are doing. It takes some time for most students to realize that gases are definite * Presented at the Twelfth Midwest Regional Meeting of the substances with definite physical and chemical properA. C. S., Kmsm City. Mo.. May 4, 1934.
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HEMISTRY enters so intimately into almost all aspects of everyday life that every intelligent person should know something about it. Chemistry teachers and textbook writers, however, have introduced so much abstruse theoretical and technically difficult matter into the first part of the beginning course that many prospective students are scared away from the subject while a large proportion of those who "take" it obtain no clear or permanent ideas concerning it. No other branch of scientific instruction has been the butt of so many gibes and reproaches from former students who, in later life, became critical and articulate enough to express themselves effectively on the subject. Two types of elementary chemistry instruction are clearly called for: first, a general, largely empirical, descriptive, or "cultural" course for all students; second, a more theoretical course for those intending to become chemical "majors" and those who need a sound knowledge of chemical theory as a basis for their special work in other fields, such as engineering, medicine, physics, biology, geology, etc. Many schools find it economically impossible to give these two courses. It is the purpose of this paper to suggest how they may be effectively combined, so that the demands of both classes of students will be met. The plan recommended involves, approximately, an inversion of the present conventional order of presenting the subject matter. Gray, Sandifur, and Hanna have made a start in this direction in their high-school chemistry text. They begin with a presentation of the physical properties of the metals. The present writer would extend this idea to include all of the common liquid and solid elements, both metallic and non-metallic, and point out the diierences between these two types of substances as the first step in the classification of the different kinds of matter. The next important point to attack is the nature of chemical reaction. A traditional method of approaching this subject is to contrast chemical with physical changes. The common blunder made in this connection is the use of vaporization and solution phenomena which in most cases involvemoleculari. e., chemicalchanges as well as phase transformations. It is also often alleged that chemical changes are more "permanent" than physical changes, in spite of the fact that many chemical changes are readily reversible.
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ties, that they can be measured, both volumetrically and gravimetrically,that they can be taken up by liquid and solid elements in chemical reactions and expelled again by suitable means, and that they can combine to form liquid and solid substances. This is at f i s t all very mysterious to the beginner. The present writer would devote the &t six weeks, at least, of his beginning course to empirical, descriptive chemistry, leading up to the atomic theory. It is then time enough to take up the chemical nature of water, the gas laws, Avogadro's hypothesis, kinetic theory, etc. When an adequate foundation has been laid, the systematic treatment of the elements-usually occupying the latter part of the course--can be rapidly presented, and no time, in the end, need be lost. A very satisfying feature of this plan is that most students, after observing and learning a considerable number of new and surprising facts, develop an intense curiosity and fairly "eat up" theory as soon as they realize the necessity of finding some explanation of what they have seen. The common attempt to impose theory upon them at the outset, for its alleged "philosophical" value, and the subsequent endeavor to "illustrate" the theory by means of involved, complicated experiments, seems to this writer to be a complete inversion of rational pedagogy. Many students stumble through a whole year of chemistry without ever realizing the essential cheinical diierence between metals and non-metals. This is another reason for introducing a classification of elements-at once simple and fundamentalat the outset of the course. The question of acids, bases, and salts can then be taken up at an early stage, without any formulas or other theoretical trimmings. Perhaps the most striking and effective method of presenting this topic is to treat a metal and a non-metal simultaneously in the same way. Sodium, burned, gives a basic oxide; phosphorus gives an acid oxide. Sodium oxide plus water gives a base; phosphorus oxide plus water gives an acid. Base plus acid gives salt (plus water). The present writer would conclude the 6rst half, or two-thirds, of his elementary chemistry course with this general survey of chemical fact, including very little theory, and that only from an empirical or descriptive viewpoint. Students who have no intention of specializing in chemistry, or in any of the other sciences or caUmgs which require chemical theory as a basis, might well drop the course at this point. They will have had enough to enable them to follow with some degree of comprehension the practical applications of chemistry to everyday life and to understand references to chemical phenomena which may occur in their general reading. The loss of students at this juncture will be more than compensated, the writer believes, by the increased proportion of those in whom will have been developed an abiding enthusiasm for chemical study, many of whom are now repelled at the outset by the unpedagogical, traditional*method of presentation. The latter part of the course may be organized in an entirely different way. If the policy outlined above
has been followed, the "advanced" class will be composed largely of students with some aptitude for scientific study, a specific interest in chemistry, and some ability for abstract thought. Having become familiar with many chemical reactions and relationships, they will have a reasonable chance of being able to understand chemical theory. They will also, presumably, be by this time fairly well along in their mathematics courses. If they have any flair at all for science, their curiosity will have been aroused. There is a real chance that the last quarter or semester, for such a class, can be profitably devoted to a systematic study of elementary physical chemistry. At this stage there is no need to be contented with merely verbalistic memorizing of definitions and theories. Nearly all the principles of physical chemistry can be illustrated by means of problems requiring no mathematics beyond high-school algebra. But if the student's real comprehension is to be tested, all problems should be worked from first pineifiles rather than from formulas. The substitution of figures for letters in formulas, followed by "cancellation," is perhaps the most idiotically fruitless academic exercise that has ever been devised. The present writer has found that a laboratory course in elementary analysis, whiie not directly related to the theoretical course at every point, is very attractive and profitable to students at this stage. There is a persistent tradition that no elementary chemistry course is complete without detailed descriptions of the "lead-chamber" and "Le Blanc" processes. "Applied" chemistry looms large in most modern texts. Pictures of crashed dirigibles, forest fires, railway wrecks, and other spectacular catastrophes are presented as typical examples of chemical reactions. While not disparaging the value of appeal to practical applications of chemistry, the writer feels that every teacher should choose those illustrations best adapted to the comprehension and local interests of his class, subordinating them to a reasonable knowledge of chemical fact and theory. Highschool and college teachers are constantly being criticized for their failure to develop in students the scientific attitude. I t has been urged that only by means of presentations of chemical theory at an early stage can the philosophical implications of the science be implanted. The writer is convinced that by bringing in these theories prematurely, the mind of the average student is merely cluttered up with masses of words and phrases which he has very little chance of understanding. If, however, a reasonable familiarity with the actual phenomena of chemistry is first ohtained, many students will show themselves able to grasp the theories. They will, moreover, be intensely interested in the subject, and will offer the enthusiastic teacher many opportunities to impart the broader lessons which can be based upon an adequate treatment of any science. No teacher can afford to miss the inspiration which comes from contact with eager students and the consciousness that "virtue has gone out of him" into intensely receptive, inquiring minds.
