1922] The Search for the Ultimate Atom 43 



If we write our old friend calomel Hg.^CU, as our chemical friends 

 tell us we should, then since CI has two isotopes and Hg has six 

 there is a total of 63 ways in which they can combine. Whether CI 

 and Hg avail themselves of all their privileges I leave it to others 

 to decide. Also whether the physiological effects of the different 

 combinations of isotopes are identical I leave to our biological friends 

 to determine. 



Various theories have been advanced as to the grouping of protons 

 and electrons in atomic structures. That the nucleus, save in the case 

 of hydrogen alone, contains both protons and electrons with protons 

 in excess, and that around this nucleus are grouped electrons equal 

 in number to the excess of protons in the nucleus, seem now to be 

 agreed upon by all. From Rutherford's experiment on the scattering 

 of alpha (a) particles the radius of the nucleus appears to be of the 

 order of 10"^^ of a cm., while the radius of the atom is of the order 

 of 10"^ of a cm. Hence the electrons constitute what may be termed 

 a planetary system, with the positive nucleus as the central sun. 



Of the theories advanced for the arrangement and behavior of 

 electrons which will explain the chemical and physical properties 

 of atoms, two are of commanding importance. 



The Bohr atom, apparently the outgrowth of the atoms of Thom- 

 son and Rutherford, was designed primarily to explain the hydrogen 

 atom and the Balmer or visible series of the hydrogen spectrum. The 

 fundamental assumption of Bohr, that the electrons rotate around 

 the nucleus in non -radiating orbits, or that an electron loses no energy 

 while it remains in the same orbit, is in harmony with our theory of 

 magnetism and furnishes a satisfactory explanation of the stability 

 of the hydrogen atom. The law of force assumed by Bohr for the 

 electrons rotating in these non-radiating circular orbits is simply 

 the Newtonian law for planetary motion. 



The second assumption of Bohr was that radiation takes place 

 only when an electron passes or jumps from a larger to a smaller 

 orbit. He assumed that the energy lost in this change is propor- 

 tional to the frequency, that it is always one quantum. 



In his energy equation to determine the possible orbits for the 

 electron Planck's constant is again involved. The equation involves 

 this constant, the orbital frequency of the electron and an integer; 

 the equation is so framed as to make the series of frequencies agree 

 with the Balmer series of hydrogen. 



