458 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



the old relationships were shown clearly. Moreover, new 

 determinations of atomic weights permitted the elements 

 Be 9*4, V 51, Ta 182, to be placed in their correct positions 

 in the table. 



Mendeleeff's first table was accompanied by the following 

 statement of the LAW OF PERIODICITY : 



" i. The elements, if arranged according to their atomic 

 weights, exhibit an evident periodicity of properties. 



" 2. Elements which are similar as regards their chemical 

 properties have atomic weights which are either of nearly 

 the same value (Pt, Ir, Os), or which increase regularly (K, 

 Rb, Cs). 



" 3. The arrangement of the elements ... in the order 

 of their atomic weights, corresponds to their so-called 

 valencies as well as, to some extent, to their distinctive 

 chemical properties, e.g. Li, Be, B, C, N, O, F. 



" 4. The elements which are most widely diffused have 

 small atomic weights. 



" 5. The magnitude of the atomic weight determines the 

 character of the element, just as the magnitude of the 

 molecule determines the character of a compound. 



" 6. We must expect the discovery of many yet unknown 

 elements, for example, elements analogous to aluminium 

 and silicon, whose atomic weights would be between 65 and 



75- 



" 7. The atomic weight of an element may sometimes be 

 amended by a knowledge of those of the contiguous ele- 

 ment. Thus the atomic weight of tellurium must lie 

 between 123 and 126, and cannot be 128. 



" 8. Certain characteristic properties of the elements can 

 be foretold from their atomic weights " (German trans., 

 Zeitschr. f. Chemie, 1869, 5, 405-406, from Russ. Chem. 

 Ges., 1, 60. English translation in Mendeleeffs " Faraday 

 Lecture," Trans. Chem. Soc., 1889, 55, 634-656). 



Lothar Meyer on periodicity (1869). A few months 

 after the publication of Mendeleeffs brief note, a paper 

 appeared on " The Nature of the Chemical Elements as a 

 Function of their Atomic Weights" (Liebig's Ann. Chem. 



