GENESIS OF THE ELEMENTS 



157 



From Rutherford's " Radio- Active Substances, etc.," 1913. 



CHAPTER VIII 



GENESIS AND TRANSMUTATIONS OF THE ELEMENTS 



IT has already been stated that the a particle is an atom of 

 helium, the atomic weight of which is 4, and that it carries 2-unit 

 charges of positive electricity. When an element loses an alpha 

 particle by radio-active change its atomic weight, therefore, is 

 reduced by 4 units as shown in many cases in the preceding tables. 

 It also changes in valency to the extent of 2 units ; as in the 

 case of radium which, like barium, is bivalent, and forms a 

 dichloride or dibromide, but when it changes into niton the 

 valency disappears and niton is found among the non-valent or 

 chemically inactive gases. 



On the other hand the separation of a /3 particle from a radio- 

 active element corresponds to a loss of 1 unit of negative elec- 

 tricity, corresponding to 1 unit of chemical valency without 

 appreciable loss of atomic weight ; the /3 particles being regarded 

 as electrons with an atom about T ^Vo" of the mass of a hydrogen 

 atom. 



If now the radio elements and their products of disintegration 

 are traced through the periodic table it appears that three 

 changes, occurring in any order, of which one is attended by 

 expulsion of one alpha particle, and two by the expulsion each 

 of a j3 particle, may result in the formation of a product which 

 remains in the same group as the parent though not in the 



