44 Journal of the Mitchell Society [September 



That the Lyman series for hydrogen is in accord with the Bohr 

 atom, althougrh Bohr announced his atom before the series was dis- 

 covered, is not remarkable ; but the very close agreement between 

 the experimentally determined value of the constant in the Balmer 

 series and the value of this constant, computed by the Bohr theory, 

 is a fact of significance. Numerous other physical facts are in har- 

 mony with the Bohr theory. Whether this theory can be so modified 

 as to furnish a complete explanation of physical and chemical facts 

 remains to be seen. 



The Lewis-Langmuir atom, proposed by Lewis and developed 

 greatly by Langmuir, is discussed at length by Langmuir in the 

 June number of the Journal of the American Chemical Society, for 

 the year 1919. As in the construction of the Bohr atom the predomi- 

 nant idea was the explanation of physical phenomena, so in the Lang- 

 muir atom the predominant idea was the explanation of chemical 

 phenomena. The guiding principle in this construction seems to have 

 been that a system in unstable equilibrium tends to pass into one 

 of stable equilibrium. Adopting an untechnical classification of the 

 chemical element suggested by Mills, we may classify the elements 

 as satisfied, unsatisfied, and dissatisfied. The radioactive elements, 

 which by ejecting alpha (a) and beta (^) particles are constantly 

 changing into other elements and finally end in lead, constitute the 

 dissatisfied. The inert gases constitute the satisfied although the 

 degree of satisfaction wanes as we pass from helium to niton. The 

 atoms between the satisfied constitute the unsatisfied and hence are 

 chemically active. 



Between neon, atomic number 10, and argon, atomic number 18, 

 lie the seven elements Na, ]\Ig, Al, Si, P, S, CI. The first three of 

 these give up electrons and are electropositive, the last three take 

 electrons and are electronegative, while Si, midway between the two, 

 avails itself of its double ]irivilege and is sometimes electropositive 

 and sometimes electronegative. 



The Rydberg formula for the atomic numbers of the inert gases is 

 N = 2 (1 -f- 22 4- 22 -f- 32 -f 3- + 4=). In the construction of his 

 shells Langmuir states he was guided by this formula. Passing 

 through the nucleus of the atom is a plane of sj^nmetry which Lang- 

 muir terms the ecjuatorial plane. No electrons lie in this ])lane. His 

 shells, on which lie the external electrons, are ajiproximately spherical. 

 The first is for helium and its radius is taken as unity. One elec- 

 tron is in each of the iiemisphorical surfaces called a cell. The elec- 



