PROBLEMS OF MODERN SCIENCE 



As a further illustration let us consider the first 

 three changes which are undergone by the radio- 

 active element Uranium. These may be repre- 

 sented by the following scheme : 



UrXj > UrX 



At. wt. 238 234 234 234 



Nu. chge. 92* 90* qie 92* 



Uranium, whose atomic weight is close to 238 

 and whose atomic number is 92, emits an a par- 

 ticle and turns into UrX x . This element, therefore, 

 has an atomic weight 234 and a nuclear charge 

 goe, e being the magnitude of the electronic charge. 

 It in turn emits a /3 particle and turns into UrX 2 , 

 which has the same atomic weight but a nuclear 

 charge one unit greater than UrX r UrX 2 emits 

 a /3 ray and forms a new element known as Ur 2 . 

 This has the same atomic weight, 234, as UrXj 

 and UrX 2 , since only /3 rays are involved in these 

 two transformations. On the other hand, it has 

 a nuclear charge one unit higher than that of 

 UrX 2 and two units higher than that of UrX x . 

 This brings its nuclear charge back to the Ur x 

 value. We have seen, however, that the chemical 

 properties of the elements are established by the 

 nuclear charges of their atoms. It follows that the 

 elements U^ and Ur 2 , which have equal nuclear 



