VALENCE AS DEFINED IN HIGH-SCHOOLTEXTS
In an earlier article in the JOURNAL OS CHEMICAL EDUCATION,' the writer has pointed out some of the difficulties confronting high-school chemistry students as the result of careless definitions in chemistry texts and careless usage of chemical terms by both teachers and texts. To emphasize the lack of agreement in the essentials of important definitions, the following report shows what a high-school student would find if he undertook to repniorce his knowledge of the meaning of valence after having read the definition given in his own text. Let it be supposed that the student intended to search among other high-school chemistry texts until he found a definition which helped clarify the conception of valence he got from the definition given in his own text. The following is a tabulation of definitions taken from sixteen widely used texts: A. B. C. D. E. F.
G. H. I. J.
The measure of the combining ability of an element--etc.-is called valence. Valence is the number of bonds which an element has-tc. Valence is the capacity of an element-tc. Va1;alence is a number which represents-tc. Valence is that property of the element-tc. Vdence is the power which an element has--etc. Valence is the number of hydrogen atoms-tc. Valence is the number of atoms qf hydrogen or of chlorine-tc. Valace is a number which expresses #u comEning capacity-tc. This difference i n holding and displlacing pmuer-is a property-we might call
valence. Tialenu is a number which expresses how many ~~~~~~~~~~tc. L. Valence i s the combining power--etc. M. Valace means the combining power-tc. N. Valence i s that property of the atom which indicates-tc. 0. T h e number of atoms of another element that one atom of a given element can hold is a wry important property--which has been given the name valence. P. Valence is the capecity of atoms t o combine with other atoms.
K.
From all this the student would learn that valence is: a property, a number. the capacity of an element, number of hydrdgen atoms, number of hydrogen or chlorine atoms. numb~rof atoms of another element, number of electrons, difference i n holding power, measure of combining ability.
T H ~JOURNAL, S
6, 7>FI
(Jan., 1929).
It is apparent that the further the student looks, the more bewildered he becomes. It would certainly be an extraordinary high-school student who would get from his search of high-school texts a very definite and accurate understanding of valence. Instead, he would probably conclude that there was no agreement among textbook writers as to the meaning of valence-r else that chemists do not know what valence is. Can any one blame the student for this, in view of the fact that no two of these definitions taken from sixteen widely used texts are in exact agreement in all essential particulars? Doesn't this show clearly that one of the pressing needs of instruction in chemistry is a standardized vocabulary? And doesn't it also show clearly that textbook writers are failing, when making definitions, to go back to fundamentals? The fact is that advances in the theoretical chemistry from 1910 to date may be clearly followed through these definitions. Some authors in revising their texts have brought their definitions up t o date while others have not. Some of these definitions are fairly good but others are mere corollaries to the true definition of valence-which if i t goes back to fundamentals must be based on the electronic theory of the structure of matter.
