532 Minster — Thermochemistry and the Periodic Laiv. 



compounds from the means of the heats of formation of the 

 chlorine and iodine. The oxygen compounds of the group are 

 not included in the diagram siuce no oxide of bromine is 

 known. The bro mates have a less heat of formation than the 

 chlorates and iodates. 



The elements in series 2 of the Periodic System stand apart 

 from the other elements in thermochemical as well as in other 

 properties. The same may be said of the elements with high 



Fig. 7. 



200 

 180 

 160 

 14-0 

 120 



100 



80 

 60 

 40 

 20 



Fig. r t 

 iodides. 



2C1 2Br 21 



Diagram of the heat equivalents of chlorides, bromides and 



atomic weights in series 10, 11 and 12, though the differences 

 between them and other elements is not so great as it is in the 

 case of the elements of small atomic weights. Series 3 to 8 

 inclusive contains subgroups of elements having characteristics 

 which vary with increasing atomic weights. The thermo- 

 chemical data of the elements in these small groups are more 

 complete than of the others and hence the study of the periodic 

 dependence of heats of combination on atomic weights is 

 limited with few exceptions to the series 3 to 8. The heat 

 equivalents of the elements of some of the subgroups in both 

 odd and even series are linear or nearly linear functions of the 



