THE PERIODIC SYSTEM 279 



General Relations in the System. In every octave the 

 valence towards oxygen ascends from one to seven, while that 

 towards chlorine and hydrogen ascends to four and then reverts 

 to one. The long series octaves therefore exhibit the same periodic 

 changes with respect to valence as do the short series octaves 

 already discussed (p. 276). Furthermore, the elements in the 

 new group on the left hand side of the table fall directly into line 

 with the rest by exhibiting zero valence. The inert gases, in other 

 words, form no compounds with other elements. The transition 

 elements on the right hand side of the table, similarly, justify 

 their position by forming a few compounds in which a valence 

 of eight is shown, for example " osmic acid " Os04. It must be 

 admitted, however, that lower valences are more frequently 

 displayed by these transition elements. 



The physical properties, both of the elements themselves and of 

 corresponding compounds, fluctuate within the limits of each 

 series in the same way. Thus the melting-points of the first 

 eight elements in the third series are as follows : 



A - 188, K 62, Ca 810, Sc - , Ti 1790, V 1720, Cr 1520, Mn 1260. 



All of the elements in the same column do not show the same 

 degree of resemblance. We find, instead, that there are two 

 well-defined families in each of the columns forming the octaves. 

 In each long series the element in the first octave falls into one of 

 these families, the element in the second octave into the other. 

 In the table on p. 278 these two families are differentiated in each 

 column by spacing one towards the left and the other towards 

 the right of the available space. Thus in the second column of 

 the table we have the family of the alkali metals (Li,Na,K,Rb,Cs) 

 and the copper family (Cu,Ag,Au). The members of the first 

 family, and their corresponding compounds, are all strikingly 

 similar in physical and chemical properties. The members of the 

 second family, on the other hand, have little in common with those 

 of the first except in their valence, and even here abnormal values 



