AN ADJUSTABLE PERIODIC CHART FOR LECTURE PURPOSES GEORGE K. ESTOK Texas Technological College, Lubbock, Texas
S o MANY forms of the periodic chart, ranging from valuable to trivial, have been published in so many places that specific references, in general, are inappropriate. Nevertheless, the variable periodic system indicated by Scheer' suggests a teaching tool which may be used to considerable advantage. An adjustable chart in which appropriate elements are k e ~within t certain movable segments has been conSCHEER, R., J. CHEM. EDUC.,32, 590 (1955).
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strutted. The conversion from the short to the long and the extra-long forms is accomplished readily. The arrangements of a,toms in the three charts are also in accord with the most commonly used forms of the periodic chart. Figures 1, 2, and 3 show the chart in three useful forms (others are also pos~ible).~ 2 The retention of obsolete symbols for elements 41, 43, and 85 is unintentional. A more recently prepitred master chart correctly identifies these as Nb, Tc, and At, respectively.
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VOLUME 33, NO. 12, DECEMBER, 1956
The sections which require movement are obvious from the photographs. Charts in these forms show the student very strikingly how the periods increase in an orderly manner, i.e., first period, two elements; second and third periods increase by 2 4; fourth and fifth periods increase by (2 4) 4; sixth and seventh periods increase by (2 4 4) 4. The figures illustrate a small model of the adjustable chart, where the movable sections are held in place by pegs and holes. For lecture purposes, however, a
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large-scale chart is required. Pegs and holes do not allow the flexibility of complete movement which is inherent in this form of chart. Two methods are suggested to assure flexibility. Sections may be attached to small magnets3 and moved readily about on a background of sheet metal, or they may have metal sliders attached which permit them t o move easily along grooved metal strips attached to the chart hoard. LIPPINCOTT, W. T..AND R. WEEATON, J. CREM.EDUC., 33, 15 (1956).
