494 Tables 603 (a) (concluded) and 603 (b) 



TABLE 603 (A) (concluded)- — Electrons, Protons, Atomic Structure 



developed this idea (Journ. Franklin Inst., 194, 213 et seq., 1922) and shown the much 

 greater frequency in nature of the even-atomic numbered elements (97.6 per cent in stony 

 meteorites, 99.2 Fe meteorites, 85.6 lithosphere, 5 unknown elements all odd, even radioactive 

 most stable). Elements below atomic number 30 make up 99.99 per cent of all meteorites, 

 99.85 igneous rocks, 99.95 shale, 99.95 sandstones, 99.85 lithosphere. The stability of the He 

 nucleus may be judged by the energy set free in the formation of He from H. According 

 to " relativity " 1 g-mass = 9 X io 20 ergs (E = mc 2 ) . The change of mass involved in the 

 formation of 1 g-atom of He (4,000 g) from 4 g-atoms of H 2 (4 X 1.0078 g) — 2.81 X io 19 

 ergs = 6.71 X io 11 calories. 1 lb. H 2 changed to He equals heat from 10,000 tons coal. The 

 nuclei of light even numbered atoms (most abundant isotope) up to Fe (26) almost wholly 

 of He nuclei. To a 1st approximation the a particle behaves in collision like an elastic 

 oblate spheroid, semi-axes, 8 X io" u and 4X io" 13 cm (Chadwick, Bieler, Philos. Mag. 

 1 921). 



TABLE 603(B). — Atomic Structure, Bohr Atom 



Bohr atom. — Bohr postulated electrons rotating in circular nonradiating orbits about a 

 central body according to the laws of celestial mechanics and its consequent energy rela- 

 tions. He added the idea that these electrons could jump between different orbits emitting 

 light of a frequency v which depended upon the relationship E2 — E 2 = hi> where the E's 

 denote the energies (according to classical conceptions) in the two orbits and h, Planck's 

 " quantum of action " of the nature of a moment of momentum. In going from one 

 possible orbit to another the moment of momentum of the electron must progress by steps, 

 each a multiple of h/2w. Balmer's formula is consistent with such a process: v = N(i/ni 

 — i/;r) where v is the frequency, N, a constant, and m for the visible series (Balmer's) 

 has the value 2, n, the successive integral values, 3, 4, 5, . . . ; 33 lines in the Balmer series 

 have been observed in stars where orbits of greater radius are possible (small gas density) 

 than in the laboratory (12 lines). With »i= 1, n, 2, 3, 4, ..., Lyman's ultra-violet series 

 results ; «i= 3, n, 4, 5, 6, . . ., Paschen's infra-red series ; m = 4, n, 5, 6, 7> • • •> Brackett's 

 series of even greater wave lengths. 



No mechanism was described to show how the energy of rotation was transferred into 

 energy of radiation nor why only certain orbits could be occupied. He evidently used non- 

 radiating orbits at variance with Maxwell's equations. 



Two independent predictions from these assumptions were verified: the predicted and 

 observed values of Rydberg's constant within \% and the differences in v for the H and 

 the He -f lines due to the 4-fold mass of the He + nucleus. 



Relativistic considerations. — Sommerfeld ( 1916) applied Einstein's relativity con- 

 siderations together with the variation of mass with the speed of the revolving electrons 

 and brought further support to the idea of orbits through prediction and the verification 

 of the " fine structure of spectrum lines." Bohr considered only circular orbits in which 

 the speed of rotation is constant, but elliptical orbits are possible with the same h/2w as 

 the circular and in them the speeds of revolution of the electrons change in different por- 

 tions of the orbit as with classical mechanics but these speeds are such that a relativity 



Smithsonian Tables 



