JOURNAL OF CHEMICAL EDUCATION
A PERIODIC TABLE FOR THE LECTURE. ROOM FRANK J. FORNOFF, GLENN I. POST, RICHARD N. RHODA, and HERMAN E. COLLIER, JR. Lehigh University, Bethlehem, Pennsylvania
METHODS of making visual the periodic character of a number of the properties of the elements are most important to teachers of general and inorganic chemistry. A number of recent papers deal with such representation~.'-~ Attractive as these suggestions are, some are not applicable to use in a lecture room and those which are show only one or two properties. I t is possible to correlate much chemistry with atomic and ionic sizes, but certainly it would be helpful for the students, a t least occasionally, to be able to see periodic relations of other properties. The recent completion of a large (14 ft. 9 in. X 6 ft.) periodic table (Figure 1) in our lecture room and our previous efforts6 at represeuting properties on a small scale have led us to investigate a plan moreversatilethan others for showing periodic properties to a large class. Our plan is to assign to each element for each property to be studied a square cardboard block marked off, at least in theory, into 100 smaller squares. The magnitude of the numerical value of the property for the element is representedbyanappropriatenumberofthesmallsquares with usually some fraction of an additional square. One counts off the squares from the lower left, moving from left to right along a horizontal row. After the completion of one row, the next higher one is begun at the left. For example, for the melting points shown in Figure 2, the 100 small squares represent 3850°K. For lithium, melting point 45Z°K., a total of lla/4small squares, 10 in the bottom row and a small section of the left side of the next row, are required. When this CAMPBELL, J. A., J. CHEM.EDUC., 23,525 (1946). CAMPBELL, J. A_,ibid., 25, 558 (1948). a GARRETT, A. B., ibid., 25, 544 (1948). KELLER, R. N., ibid., 28,312 (1951). 6 I~NGENB J.,EAND RG L. ,SPRINGMAN, *id., Z9,81 (1952). 6 WAZLEHURST, T. H., AND F 3. FORNOFF, ibid., 20.77 (1942). I
method is used for small-sized tables,=the proper number of squares is darkened. For our lecture room use the proper area was laid out on a card six inches wide and a maximum of six inches high (not countiug the inch flap a t the bottom for mounting), and the card was then cut to include only this area. Wood strips with 1 in. X 1 in. cross section and as long as the differentperiods required were obtained and painted dull black. Four stranded wires were hung from hooks above the lecture-room periodic table, and the wood strips were attached to the wires at the aDvro.. priate horizontal levels for the different periods. The strips were bored for the wires, or the nires were stapled to the ends of the strips as each location required. A romparison of Figure 1with Figure 2 shows the location of the strips. This framework was then used for mounting the previously described property cards, one for each element. Our periodic-table block for each element is 7 in. X 9 in. The property card, 6-in. wide and a t most 6-in. high, is attached to the wood strip to cover a portion of the symbol of the element, but the atomic number is left exposed for ready identification of the element from a textbook periodic table or list of elements. We use yellow cards to contrast best with our white table and its blark, green, and orange symbols, black atomic weights, and red atomic numbers. The flap on each card for the thumb-tack attachment is covered with black picture-binding tape, and blaclc-headed thumb tacks are used. The fastening can thus be done on the front side of the wood strips without leaving any disturbing evidences of the attachment. Both horizontal and vertical relationships among the elements for the property displayed are obvious to the entire class a t the same time. This method makes apparent variations in the magnitude of properties in a
DECEMBER, 1952
Figure 1.
The periodic t a b l e of lecture roam sire s h o w n with t h e lights o n and without t h e frame used in showing the periodic relation..
small space even wheu the variatiotls are rat,her small. Notice, for example, t,hat t,he irregnlarit,ies in the melt,. ing points of t,hc alkaline earth metals are readily apparent,. The photograph for t,he figure was retouched t,o show t,he out,lines of the cards sinre the yellow-white color contrast is not rccordcrl hy phot,ographic film. Ally Iargc periodic tahle may he used for this sort of property display. Our tahle h i ~ sthe feature of separately rontrollcrl lights for earh of the elemeuts. We
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621
vim t l n ~ sillumit~at,et,he hlocl~for the element iu ear11 period with t,he highcst or t,he lowest value of t,he propcrt,y a d so make quite striking the regularity-or t,hc stlift,s-ill t,hr locations of these estrcmes from O I I ~ period t,o the nest. Wit,h some planning a ~ some l preparatiw for t,hc t,hnmh-tark attachments, one can shift. from one set of property rards to anot,her in fairly short order, but one \vould ~ a r e l ywant to take class time for t,his. We havc not found that heing forced to take up only one property
Periodicrepresentationof themeltingpointsoftheeiementr. The magnitude of the area of t h e card in front of the r y m b a i is a measure of the melting point of the element.
JOURNAL OF CHEMICAL EDUCATION
(2) The network of metal boxes, one for each element, was constructed of 18 vertical and nine horizontal strips, appropriately slotted to permit the egg-crate type of interlocking. In order that the strips might be drawn tight, the method of attachment shown in Figure 3 was used. Other constructional details are also shown in this figure. The entire network is mounted in a wood frame which is set into and attached to the iron angle-pieces which constitute the outer frame of the table. The network is thus not fastened t o the backhoard and so can be removed as a unit if this becomes necessary. Although measurement for the dotting was carefully done, we found it necessary t o glue narrow strips of paper into many of the box corners to reduce light leakage from one box to its neighbors. (3) The glass used is white opal. The symbols are on the front of the glass, and with the white background we have a most effective table whether illuminated or not. The lights were off for Figure 2 and were on for Figure 1. The light transmitted is somewhat reduced by this choice of glass, but glass wool was not used in front of the bulbs, and we still have very good light diffusion as shown in Figure 1. (4) The use of transparenciess and of decals8 for atomic numbers and weights obviated the need for a painter. An adhesive-backed cloth tape was used for the lines. We found it possible t o get a variety of colors in transparencies of the right sizes, and so we employed differentcolors for the symbols to show which elements are in each of the three states of matter a t room temperature. Each letter, number, and period is a separately applied unit. (5) To suggest the chemical relationships as fully as possible the symbols for thorium, protactinium, and uranium, as well as those of lanthanum and actinium, appear twice on the tahle. in a period, along with the other material for the re- For each of these elements one switch controls both mainder of the class time, is necessarily bad. Too lights, but the colors of the bulbs are those required for many periodic properties in one day make a difficult the families in which the dual relationships place the body of material for the students to understand and elements. Prospective builders may be interested in our cost master. Considering one property per class for a few days encourages discussion. We have, for example, ex- fignres : plored explanations for the interesting variations of melting points within each family and from family to family. The elements with no cards can be easily located, and the class can develop periodic understanding Lumber 26.14 by making predictions for missing values. The frame, 51.00 Decals, transparencies Hardware (bolts, screws, etc.) 34.60 after the cards have been removed, may be left in place IMiscellmeour 25.04 over the periodic table, or it may he removed and rolled up for compact storage. The cards for any one propThese costs include the framework and the cards for erty may be easily stored in a large manila envelope. Our periodic table, although much like the one con- the periodic property representations. We had no structed by F. B. Duttou' a t Michigan State Col- labor costs and have not dared estimate the time used lege, has several variations that may be of in- on the project. Talking to another builder would no terest to others: (I) Our back piece is of fiber- doubt have saved us much time. The usefulness and attractiveness of the table as a board rather than plywood. The fiberboard comes in sheets almost large enough for a table of our size with- teaching aid in presenting the periodic and other propout seams. We have covered the hack with two coats erties of the elements have led us to feel that our inof aluminum paint rather than with sheet aluminum. vestment of time and money was worth while.
'D ~ o NF.,B., itid., 28, 110 (1951).
Addresses of manufacturers will be furnished on request.
