from the Physico- Chemical Standpoint. 329 



in the uranium atom, since it ejects eight a-particles in suc- 

 cession, there will be at least sixteen such systems. The 

 ejection of the charged helium atom is supposed to take place 

 when two of these complexes collide with one another either 

 owing to a crossing o£ their orbits or by a disturbance o£ the 

 stability conditions within the atom; and the collision pro- 

 duces a group of four positive and two negative charges, the 

 arrangement of which will be clear when the next zone of 

 the atomic structure has been considered. 



The atomic number of the element and the general chemical 

 character of the atom are governed by the nature of the two 

 inner sections of the atomic system. A change in either the 

 negative core or the intermediate positive zone alters the 

 nature of the intra-atomic system and thus brings about a 

 modification of the structure as a whole. 



The external zone of the atom is. the portion influenced by 

 normal reactions resulting in chemical change or alteration 

 in valency. The assumption that the orbits of the electrons 

 in this zcne are cometary in type has been made for the 

 following reason. When the " cometary Si electrons in their 

 paths about the centre of the atom reach a position of aphelion 

 to the nucleus, they will be travelling slowly in their orbits 

 and hence will be less resistant to forces tending to remove 

 them from the atom. Further, since they are far away from 

 the centre of attraction under these conditions, the forces 

 uniting them to it will be weakened ; and it will be possible 

 to abstract or insert electrons at this point much more readily 

 than is the case with electrons in either of the other two 

 zones. This serves to account for the ease with which the 

 valency of certain elements can be altered by chemical or 

 electrical means. In the case of elements which show no 

 changes of valency, it may be assumed that the electronic 

 orbits in the outer zone are more nearly circular inform than 

 is the case with elements exhibiting variable valency. The 

 inertness of the argon series is accounted for by assuming 

 that in their case the attraction of the nucleus under normal 

 conditions is insufficient to retain any electrons in an external 

 zone. 



At this point it may be well to indicate the conditions of 

 attraction within the systems of ordinary elements ; and the 

 point may be illustrated by means of a metallic atom such 

 as tin. In this case, the negative charges at the centre are 

 assumed to be fewer in number than the charges in the 

 positive zone. Owing to this preponderance of positive 

 charges, the positive-negative nucleus as a whole will have 

 a positive charge ; and, acting as a unit, it will suffice to 



Phil. Mag. S. 6. Vol. 36. No. 214. Oct. 1918. Z 



