GENESIS OF THE ELEMENTS 



165 



are led to believe their atoms consist. The non-metallic substances 

 placed in Groups V, VI, and VII of the periodic scheme, on the 

 other hand, are very dissimilar from one another in obvious 

 properties ; fluorine and chlorine, nitrogen and oxygen are gases 

 at common temperatures, while bromine is a liquid, and phos- 

 phorus, sulphur, and iodine are solids. They form well-defined 

 groups, but instead of their negative activity increasing in pro- 

 portion as the atomic weight increases, they lose much of this 

 character, and gradually assume more or less completely the 

 appearance and properties of metals. Moreover the number of 

 non-metals is relatively small when compared with the elements 

 which exhibit more or less definitely the characteristics of the 

 metals. Leaving aside the five indifferent gases of the argon 

 family and hydrogen, we may count thirteen non-metals in the 

 list of elements, while all the rest, numbering upwards of sixty, 

 are metals. 



The discovery of helium as a product of the disintegration of 

 the radio-active elements is suggestive when coupled with the 

 fact that in passing from series to series in the periodic table the 

 difference in the atomic weights of the common elements is 

 approximately a multiple of 4. Take the first three rows of 

 elements after hydrogen ; they stand as follows : 



Reviewing these figures it will be seen at once that the differ- 

 ence between the first and second row of elements is uniformly 

 very close to 16. The differences between the second and third 

 rows vary somewhat, inasmuch as three are very near to 16, 

 while in four cases they are very near to 20. Both these numbers 

 are multiples of 4, which is the atomic weight of helium. 



The view which appears to be held, by those who have devoted 

 themselves to the study of radio-active phenomena, concerning 

 the constitution of the atom is somewhat as follows : The mass 

 of the atom is associated with positive electricity which is 

 neutralised by electrons, each carrying unit charge of negative 

 electricity. There is a difference of opinion as to whether the 



