JOURNAL OF CHEMICAL EDUCATION
590
A VARIABLE PERIODIC SYSTEM RODERICH SCHEER Waldoberschule, West Bedin, Germany
S T U D E X T S often have difficulty seeing the connection between the two usual forms of the periodic system, the one in short and the other in long periods. The system I am about to describe is variable. It consists of separate little cards, one for each element, mhirh are huug up on a hoard. This enables the system to he used in the two forms interchangeably. .
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The cards are rolored m follows: H, dark blue; first group (Li), light blue; second group (Be), white; third group (B), green; fourth group ( C ) , black; fifth group (N), hrick red; sixth group (O), y e l l o ~ ~ ; seventh group (F), light red; eighth group (inert gases), gray. This system has two characteristics. First, the
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Figure 2 .
Short Form
NOVEMBER, 1955
cards of the lanthanides as well as those of the actinides (Ac, Th, Pa, U, and the transuranides) all hang on the same nail. In the same manner the iron metals (Fe, Co, Ni), light platinum metals (Ru, Rh, Pd), and heavy platinum metals (Os, Ir, Pt) form one block each, on separate nails. Second, there is a column after the fourth, fifth, and sixth periods which is vacant while the system is used in the long-period form; herein the system differs from the colokd system in long periods by A. vou Antropoff. In order to call special attention to the principal groups, the spaces between the elements are covered with blank cards. It is easy to change from the long- to the shortperiod form. Figure 3 shows the fourth period; large numbers are elements of principal groups and small ones of the subgroups. First, the second half of the period is lowered one row. Then the upper half is spaced out to the right and the lower half to the left. It now will be seen that the elements of the first and second principal groups are to be found in the upper left-hand corners and those of the other principal
591
groups in the lower right-hand corners of their respective fields, which is characteristic of every short-period system. Now vacant spaces are filled with blank cards as mentioned, to facilitate identification of principal groups. Blocks of cards can be substituted in the system itself bv one card with soecial letterine. like 26-28 or 57-fl. These blocks can be separaGd and hung on nails specially installed below the actual syst,em.
F i g " . .
3.
Tlanrforrnin. the Fourth Peziod
