566 WYCKOFF: FORCES BETWEEN ATOMS IN SOLIDS 



of these papers. Recently I. Langmuir^ has extended the theory 

 of G. N. Lewis and has also tried to obtain from purely chemical 

 considerations information about the more intimate structure 

 of the atom. A. L. Parson^ has applied his "magneton" theory 

 of the atom to an explanation of chemical forces. 



THE STRUCTURE OF THE ATOM 



The "nucleus atom." — An accurate relation has been shown 

 to exist between the wave lengths of the X-rays characteristic 

 of the various elements and their order numbers in the periodic 

 table.' This relation was discovered after the importance of 

 this order number, known as the "atomic number," had already 

 been urged. ^ Its bearing on the structure of the atom will be 

 seen from the following facts. 



If alpha particles are shot at a substance, a certain number 

 of them will suffer a large change in direction. The "scatter- 

 ing" (change in direction) actually observed in the case of the 

 various elements is that which would be expected if the atom 

 possessed at its center a minute positively charged nucleus.^ 

 Experiments indicate that this charge has a magnitude Ne, 

 where e is the charge on the electron and N is the atomic num- 

 ber. ^° Further, a study of the disintegration products of ura- 

 nium and thorium shows clearly the variation of the chemical 

 properties with variations in the nuclear charge. ^^ These facts 



^ I. Langmuir, The arrangement of electrons in atoms and molecules. Journ. 

 Amer. Chem. Soc. 41: 868-934. I9i9- 



^ A. L. Parson, A magneton theory of the structure of the atom. Smithsonian 

 Misc. Coll. 65: No. II (Publication No. 2371). 1915. 



' H. G. J. MosELEY, Phil. Mag. (6) 27: 703-713. 1914. If N is the order num- 

 ber of the elements, beginning with hydrogen as one, helium as two, lithium as three, 

 etc. ; V the frequency of the corresponding lines in the X-ray spectra ; A a constant 

 which is the same for all elements; and b a similar constant having a value less 

 than unity, then 



!> = A{N—by-. 



^ A. VAN DEN Broek, Physik. Zeits. 14: 32-41. 1913. 



^ E. Rutherford, Phil. Mag. (6) 21: 669-688. 191 1; etc. 



1" H. Geiger, Proc. Roy. Soc. A. 83: 492. 1910. 



'1 F. SoDDY. The chemistry of the radio-elements . II. The radio-elements and the per- 

 iodic law, p. 2. 1914. The loss of an alpha particle (doubly positive helium- 

 atom) decreases the nuclear charge by two units producing an element placed two 

 positions to the left in the periodic table. The loss of a beta particle (an electron) 

 produces a shift of one unit in the opposite direction. 



