MENOELEEV'S LAW: A DEMONSTRATION
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Submitted by: Kenneth Emerson, Montana State University, Bozeman, Montana 59715 Tested By: Edward B. Rosser, Hiram College, Hiram, Ohio 44234
PREPARATION
REMARKS
Provide about 35 colors of tissue paper cut into 5-in. circles and backed with 1/16-in. poster board. These discs are laid out in a periodic color order of red, orange, yellow, green, blue, indigo, and violet with successive periods increasing in color intensity. They are then numbered consecutively choosing each successive number in an arbitrary fashion. Some decimal numbers may be used and gaps may be included in one or two of the periods. A small magnet or tape or similar adhesive is needed for each disc so it will adhere to the blackboard. DEMONSTRATION
When the discs are properly arranged the periodically repeating sequence of colors should show up and the suggestion of arranging the periods one under another should come forth. The vacancies will appear and can lead to predictions such as Mendeleev made about eka-manganese (Tc), dvi-manganese (Re), and eka-silicon (Ge).' Problems can be p r ~ p o s e d . ~ The never ending effort to improve and extend the table (to element 168) can be discussed and the recent proposal of periodicity within the lanthanides pointed out.S
The discs are scattered in complete disorder across the blackboard, representing the elements as they must have appeared to Mendeleev. The properties are represented by colors. A couple of students are invited to arrange the discs in numerical order.
'HILDEBRAND AND POWELL," Principles of Chemistry," (7th ed.), The l\lacmillan Co., New York, 1964, p. 22. HILDEBEAND and POWELL,p. 24. 8 Chem. and Eng. News, 47, 45 (Apr. 28, 1969).
Volume 47, Number I , Jonuory 1970
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