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A VALENCE-NAME-FORMULA-SOLUBILITYCHART G.N.QUAY,Cos COLLEGE. CEDAR-IDS,
IOWA
The author of every elementary text-book of general chemistry endeavors to present the need and usefulness of symbols and formulas very early in the course in a way that will make it easier for the student to retain a reasonable working knowledge of the subject. Every teacher, however, realizes that the student is confronted with a new means of expression and requires considerable drill in order to acquire the working knowledge desired. As helps in the study of formula writing, short lists of common negative and positive radicals are to be found in some texts, and tables of prinapal valences of elements in some hand-books. A name and formula chart, patented by C. D. Poore (1905), contains the more common negative and positive radicals grouped separately in order of valence. The writer has found the use of a modification of this chart very helpful in his classes in general chemistry. Solubility tables found in text; and band-books are of two general types: those giving numerical values and those giving relative solubility by use of symbols. The former and more useful type are found in such textbooks of general chemistry and qualitative analysis as those by Deming, Test and McLaughlin, Schlesinger and Holmes. The chart described herewith has resulted from the writer's effort to help students acquire more quickly not only a working knowledge of valence and formula writing but also a more definite familiarity with both relative and numerical solubility values of the more common compounds. The numerical solubility values have been taken from a number of sources. The nature of the chart would not permit reference directly nor by key. Of the more elaborate sources, Seidell's Solubilities of Inorganic and Organic Substances, was used; hand-books of recent edition to which reference was made include Van Nostrand's Chemical Annual, The Hand-Book of Chemistry and Physics published by the Chemical Rubber company, The Chemists' Year Book edited by Atack; and tables contained in the following texts were consulted for additional data or used for the purpose of checking: General Chemistry by Holmes, General Chemistry by Deming, General Chemistry by Schlesinger, and Notes on Qualitative Analysis by Test and McLanghlin. The relative solubilities in the Valence-Name-Formula-Solubility chart are indicated by half or full bars near the upper or lower edges of the rectangles representing compounds. Where numerical data were not found the symbols used in certain tables were translated into the form used here. Such tables are to be found in Analytical Chemistry, Volume I, by Treadwell and Hall, the Van Nostrand Chemical Annual, and the Hand-Book of Chemistry and Physics.
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VALENCE
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NAME -FORMULA
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I CHART
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The negative radicals are arranged at the top of the chart in groups in order of increasing valence while the positive radicals are arranged in a vertical column at the left edge in the same order. The attempt has been made to keep the radicals in the order in which the elements appear in the periodic table as nearly as such an arrangement would permit and the valence of each is indicated by plus or minus signs in order that the student will be reminded of valence by groups and individually. It is apparent that each rectangle formed by the cutting of the horizontal lines for the positive radical and the vertical lines for the negative radical represents a possible compound and further, that the sections of small rectangles formed by the cutting of lines representing like valence for the positive and negative radicals, respectively, can be represented by a type formula. If we let M represent the positive radical and X the negative radical, MX is the type formula of any compound formed by a monovalent positive radical and a monovalent negative radical such as NaCI. MzXl may represent a compound like Fez(S04)a and so on. A student can, therefore, by noting the type formulas, write the correct formula of any compound possible by combining any of the 32 positive radicals with any of the 34 negative radicals. The key at the lower edge of the chart indicates what each character represents. By observing the position of the full and half bars the student can quickly learn what compounds having a common positive radical or what compounds having a common negative radical are soluble in water, sparingly soluble in water, etc. For example: insoluble salts of potassium are KzPtCls and KaCo(NOz)s; insoluble chlorides are AgCl, HgC1, TlC1, PbC12. The numerical data afford an opportunity for closer study of solubilities of groups of compounds and can also be used in the solution of problems where solubility data is required. As an illustration it will be noted that the order of decreasing solubility of the halides of silver is in the order of increasing atomic weight of the halogens. Blank spaces warn the student that the compound represented is either unknown or that it decomposes readily in water. Like any other orderly grouping of chemical compounds the chart invites closer study of the physical and chemical properties of the related compounds. The chart is not planned to include all the radicals used in general chemistry courses but the attempt has been made to include the more common ones. The only excuse for presenting the chart in its present form is that the writer is satisfied that it has served a useful purpose in his classes.
