280 SMITH'S INTERMEDIATE CHEMISTRY 



are shown in well-known compounds such as cupric salts, which 

 contain the radical Cu 11 . 



The inert gases, on the left of the octaves, constitute a single 

 family. As for the transition elements on the right, while the 

 three members in any one series resemble one another in many 

 respects, yet a closer relationship between elements in different 

 series, according to the vertical arrangement shown in the table, 

 dividing the group into three families, is also evident. 



If we examine the physical properties of successive elements, 

 or corresponding compounds of successive elements, of any one 

 family we find a uniform gradation observable, just as in the cases 

 of the halogens and their hydrogen compounds studied in chapter 

 XVII. Thus the melting-points of the alkali metals are as follows : 



Li 186, Na96, K62, Rb38, Cs26. 



As yet no exact mathematical (quantitative) relation between 

 the values for any property and the values of the atomic weights 

 has been discovered; only a general (qualitative) relationship can 

 be traced. Anticipating the discovery of some more exact mode 

 of stating the relationship in each case, and remembering that 

 similar values of each property recur periodically, usually at inter- 

 vals corresponding to the length of an octave or series, the prin- 

 ciple which is assumed to underlie the whole, the periodic law, 

 is stated thus: All the properties of the elements are periodic 

 functions of their atomic weights. 



That the chemical relations of the elements vary just as do the 

 physical properties of the simple substances is easily -shown. 

 Thus, each series begins with an active metallic (positive) element, 

 and ends with an active non-metallic (negative) element, the inter- 

 vening elements showing a more or less continuous variation 

 between these limits. Again, the elements at the top are the least 

 metallic of their respective columns. As we descend, the members 

 of each group are more markedly metallic (in the first columns), or, 

 what is the same thing, less markedly non-metallic (in the later 

 columns). 





