88 SCIENCE REMAKING THE WORLD 



sional scintillations may be observed at a much greater 

 distance from the radioactive material. Now, hydro- 

 gen has long been known to be an atom with a single 

 proton for a nucleus and, of course, one planetary elec- 

 tron. These scintillations are due to these protons 

 which, being lighter than the alpha particles, are thrown 

 farther by the collision. When pure nitrogen is used 

 there are occasional scintillations at that greater dis- 

 tance which corresponds to a single proton being pro- 

 jected forward by the collision. 



In the radioactive atoms the nucleus is most expres- 

 sive but in all atoms it is the real determining influence. 

 Upon it depends the number of planetary electrons, 

 for their number is normally equal to the excess of pro- 

 tons in the nucleus. Upon this number depends the 

 configuration and that determines the chemical behav- 

 iour of the atom. In final analysis the nuclear content 

 makes the atom what it is. For that reason it is con- 

 venient to classify on a purely numerical basis by the 

 "atomic number" which states the excess of protons in 

 the nucleus. 



For purposes of visualizing the chemical behaviour 

 of atoms it is simplest to deal with those of atomic 

 numbers n and 17 which are sodium and chlorine, 

 respectively. Now it happens that the atom of atomic 

 number 10 is that of neon, an inert gas, much like helium 

 except heavier, which is completely satisfied. The 

 atomic number 18 denotes another satisfied structure, 

 that of argon. Sodium and chlorine, however, were 

 created without the complete satisfaction of both the 

 urges which were mentioned earlier. Sodium has one 



