A CONVERTIBLE PERIODIC TABLE FRED. Y . HERRON University of Pittsburgh, Pittsburgh, Pennsylvania
the extended-type of periodic table, having all of the elements of each period on a single horizontal line, has become popular. This modification has a number of advantages over the older or Mendeleev type but, in the experience of t,he %uthor,has the disadvantage of being less readily understood by beginning students. The cause of this difficulty is probably t,he failure of most elementary textbooks to explain the relationship between the two forms of the table in sufficient detail. In the opinion of the author, the fact that a period, in either form of the table, consists of elements having the same number of electron levels has not been sufficiently emphasized. He has been surprised to find, in showing to other teachers the device vhich is about to be described, that many of them were either not aware of this fact or did not realize its importance in explaining the transition from the condensed to the extended type of table. In an effort to make clear h o the ~ new type of table has been evolved from the old, the author has designed a periodic table having movable parts constructed so that, by merely changing their position, either type of may be formed' Figure shows the pa*s ranged in the condensed Or figure shows the device with the movable parts out of position. Figure 3 s h o the ~ parts arranged in the newer extended form.
This device is not intended to be a complete periodic table, Its purpose is merely to show the relationship between the two forms. For this reason it has been simplified as much as possible. Only the atomic number and the number of electron levels are given and the lanthanide and actinide seriesare not shown in detail although thei~. positions in the body of the table are indicated, It emphasizes the that, in the newer form the elements are arranged in order of their atomic numbers just as in the old firm; that a period in either form consists of elements having the same number of electron levels, and that the principal novelty in the newer form is the placing of all the elements of each period on a single line.
The table pictured in the accompanying photographs was made on a 1/4-in. plywood base painted white, while the lettered portions were made of '/&-in. beaver board also painted white. The fixed portions were nailed to the wood base. The movable pieces have holes drilled in them by means of which they hang on small finishing nails driven into the base. These nails
and holes are so located that each movable piece may hang in either of two positions depending upon which type of table is to be illustrated. The lettering and lines are all in black except the figures indicating the number of electron levels which are in red for emphasis. The over-all size of the table is approximately 48 by 29 in., each of the small divisions being 21/2 in. square.