Chronology of Milestone Events in Particle Physics - BOHR 1913B
Chronology of Milestone Events in Particle Physics

  Nobel prize to N. Bohr awarded in 1922 "for his investigation of the structure of atoms, and of the radiation emanating from them''  

BOHR 1913B

Bohr, N.;
On the Constitution of Atoms and Molecules. II.
Phil. Mag. 26 (1913) 476;

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S 1. General Assumptions.
Following the theory of Rutherford, we shall assume that the atoms of the elements consist of a positively charged nucleus surrounded by a cluster of electrons. The nucleus is the seat of the essential part of the mass of the atom, and has linear dimensions exceedingly small compared with the distances apart of the electrons in the surrounding cluster.
As in the previous paper, we shall assume that the cluster of electrons is formed by the successive binding by the nucleus of electrons initially nearly at rest, energy at the same time being, radiated away. This will go on until, when the total negative on the bound electrons is numerically equal to the positive charge on the nucleus, the system will be neutral and no longer able to exert sensible forces on electrons at distances from the nucleus (treat in comparison with the dimensions of the orbits of the bound electrons. We may regard the formation of helium from rays as an observed example of a process of this kind, an particle of this view being identical with the nucleus of a helium atom.
On account of the small dimensions of the nucleus, its internal structure will not be of sensible influence on the constitution of the cluster of electrons, and consequently will have no effect on the ordinary physical and chemical properties of the atom. The latter properties on this theory will depend entirely on the total charge and mass of the nucleus; the internal structure of the nucleus will be of influence only on the phenomena of radioactivity.
From the result of experiments on large angle scattering of rays, Rutherford found an electric charge on the nucleus corresponding per atom to a number of electrons approximately equal to half the atomic weight. This result seems to be in agreement with the number of electrons per atom calculated from experiments on scattering of Röntgen radiation. The total experimental evidence supports the hypothesis that the actual number of electrons in a neutral atom, with a few exceptions, is equal to the number which indicates the position of the corresponding element in the series of elements arranged in order of increasing atomic weight. For example on this view, the atom of oxygen which is the eighth element of the series has eight electrons and a nucleus carrying eight unit charges.
We shall assume that the electrons are arranged at equal angular intervals in coaxial rings rotating around the nucleus. In order to determine the frequency and dimensions of the rings we shall use the main hypothesis of the first paper, viz.: that in the permanent state of an atom the angular momentum of every electron round the centre of its orbit is equal to the universal value h / 2 where h is Planck's constant. We shall take as a condition of stability, that the total energy of the system in the configuration in question is less than in any neighbouring configuration satisfying the same condition of the angular momentum of the electrons.
If the charge on the nucleus and the number of electrons in the different rings is known, the condition in regard to the angular momentum of the electrons will, as shown in S 2, completely determine the configuration of the systems i.e., the frequency of revolution and the linear dimensions of the rings. Corresponding to different distributions of the electrons in the rings, however, there will, in general, be more than one configuration which will satisfy the condition of the angular momentum together with the condition of stability.
In S 3 and S 4 it will be shown that, on the general view of the formation of the atoms, we are led to indications of the arrangement of the electrons in the rings which are consistent with those suggested by the chemical properties of the corresponding element.
In S 5 it will be shown that it is possible from the theory to calculate the minimum velocity of cathode rays necessary to produce the characteristic Röntgen radiation from the element, and that this is in approximate agreement with the experimental values.
In S 6 the phenomena of radioactivity will be briefly considered in relation to the theory.

Related references
More (earlier) information appears in
N. Bohr, Phil. Mag. 26 (1913) 1;
More (later) information appears in
N. Bohr, Phil. Mag. 26 (1913) 857;
Analyse data from
A. van den Broek, Phys.Zeitschr. 14 (1913) 32;
R. A. Millikan, Brit. Assoc. Rep. (1912) 410;
P. Gmelin, Annalen der Physik. Leipzig 28 (1909) 1086;
A. H. Bucherer, Annalen der Physik. Leipzig 37 (1912) 597;
E. Rutherford, Phil. Mag. 24 (1912) 893;
J. J. Thomson, Phil. Mag. 24 (1912) 218;
J. Frank, Verhandl. Dtsch. phys. Ges. 12 (1910) 613;
J. Frank, G. Hertz, Verhandl. Dtsch. phys. Ges. 15 (1913) 34;
J. W. Nicholson, Month. Not. Roy. Astr. Soc. 72 (1912) 52;
J. W. Nicholson, Month. Not. Roy. Astr. Soc. 73 (1913) 382;
R. Whiddington, Proc. Roy. Soc. A85 (1911) 323;
E. Rutherford, Phil. Mag. 24 (1912) 453;
C. G. Barkla, Phil. Mag. 21 (1911) 648;
H. Geiger and E. Marsden, Phil. Mag. 25 (1913) 604;
J. J. Thomson, Phil. Mag. 23 (1912) 456;

  atom* atom p

Particles studied
  atom mass, qn
  atom* mass, qn
  nucleus mass, qn

Record comments
Bohr's quantum theory of atomic spectra. Evidence that radioactivity is a nuclear property.
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