140 THE PATH OF SCIENCE 



in all. On the basis of this theory, Lewis and Irving Lang- 

 muir were able to explain the structures of many chemical 

 compounds; and the Lewis model of the nature of valency 

 has been generally accepted. One difficulty in this explana- 

 tion, however, is that the electrons, depicted by Lewis as part 

 of the structure of the atoms, were bound in position, whereas 

 in the Rutherford-Bohr atoms, the electrons were free to re- 

 volve in their orbits. In fact, the atom as pictured by the 

 physicists has never been entirely reconcilable with the prop- 

 erties required by the chemists for their atoms. Recently, 

 however, the mathematical physicists appear to have found 

 the solution for such difficulties.* By the application of quan- 

 tum mechanics, it seems that the orbital atom may provide 

 the necessary mechanism for the formation of the electronic 

 bonds required for the stability of compounds. 



Recent developments in nuclear physics have accelerated 

 the synthesis of chemistry and physics into one subject. 

 We have seen that the nuclei of the atoms are known to 

 consist of protons and neutrons, the total number correspond- 

 ing to the atomic weight of the element, whereas the number 

 of protons gives the atomic number. The atoms of nearly 

 all the elements are stable; only the few radioactive elements 

 disintegrate of their own accord. These radioactive ele- 

 ments, however, give out a great deal of energy when their 

 atoms disintegrate. The total energy given out by a pound 

 of radium in a year would convert nearly a ton of water into 

 steam, although it would take twenty-five hundred years for 

 half the radium to disintegrate. The radioactive elements, 

 therefore, indicate that an enormous amount of energy is 

 available if the nuclei of the atoms can be made to disinte- 

 grate. 



Experiments by Rutherford and his associates showed that 

 this disintegration could be accomplished Avhen the nuclei 

 were struck by particles of very great energy, such as the alpha 

 rays from radium. The breakdown of nitrogen atoms by 



* Chapter V, p. 113. 



