The use of charts in teaching general chemistry

THE USE OF CHARTS IN TEACHING GENERAL CHEMISTRY JOHN A. TIMM, YALEUNIVERSITY, NEW HAVEN, CONN. The student, who has always been the most difficult to interest in chemistry, is the one who considers it a science containing an enormous number of isolated facts which have to be memorized. He can see no connection between these fads and is, therefore, a t a loss to know how to correlate them. Such students need all the help that can be given them and any device which shows the relationship of one fact to another and points out vividly the points of similarity and difference of the various elements, is to be welcomed. The writer has from time to time advised students to construct charts

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showing the chemical reactions of each element, studied in as brief and clear a form as possible. If the student can be made to use the same logical form in constructing each chart, the differences and similarities of the elements become apparent when their charts are compared. The construction of such charts requires the student to reason out for himself the relationships of the various compounds of an element to one another and also necessitates his reviewing the chemical reactions of the elements previously studied in order that each new chart may take the same form. After using various methods of constructing such charts the form illustrated in the accompanying illustration was found to he one which could be adopted as a model after which to pattern the charts of the other elements.

VOL. 3. No. 1

USE OP CRARTS IN TEACHING GENERAL CHEMISTRY

69

The name and symbol of each element, its group in the periodic classification, and its valences are included in the first line of each chart. Under occurrence, on the next line, only the more important, naturally occurring compounds are placed. Their mineralogical names can be omitted, for the most part, except where they are of particular significance. Water of hydration can be treated in the same way. The more important compounds of the element are then 'arranged from left t o right in the order of increasing valence of the element; that is, the hydride, if it exists, is placed a t the extreme left, since in i t the element has a negative valence, followed by the free element with a valence of zero, and then the oxides, in which the valence is positive. Vertical lines are then drawn down from these formulae and are considered t o represent their respective formulae. An arrow pointing t o a line shows a method by which the compound can be prepared, whereas an arrow pointing away from the line signifies a chemical reaction into which the compound will enter. At the lower end of each line is placed the valence of the element in the compound for which the line stands. Whenever lines, which have no connection, cross, the convention employed by electrical draughtsmen is used. If i t is desired t o show, for example, that both sodium and sodium oxide can be converted into sodium chloride upon treatment with hydrochloric acid, this would he indicated as follows: Nan0

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This also shows that sodium will not yield sodium oxide when treated with hydrochloric acid. Compounds which are unstable or which have not been isolated are enclosed in brackets. On each arrow may be placed a number which refers to an equation for the reaction represented on the chart. After the student has constructed a series of charts they offer him a rapid method of reviewing the chemistry of any particular element.