Chronology of Milestone Events in Particle Physics - BOHR 1913
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 1913

Bohr, N.;
On the Constitution of Atoms and Molecules. I.
Phil. Mag. 26 (1913) 1;

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Reprinted in
The Old Quantum Theory, ed. by D. ter Haar, Pergamon Press (1967) 132.
The WORLD of the ATOM, editors H. A. Boorse and L. Motz, Basic Books, Inc. Publishers, New York - London, v.I (1966) 751.

Introduction
In order to explain the results of experiments on scattering of rays by matter Prof. Rutherford has given a theory of the structure of atoms. According to this theory, the atoms consist of a positively charged nucleus surrounded by a system of electrons kept together by attractive forces from the nucleus: the total negative charge of the electrons is equal to the positive charge of the nucleus. Further, the nucleus is assumed to be the seat of the essential part of the mass of the atom, and to have linear dimensions exceedingly small compared with the linear dimensions of the whole atom. The number of electrons in an atom is deduced to be approximately equal to half the atomic weight. Great interest is to be attributed to this atom-model; for, as Rutherford has shown, the assumption of the existence of nuclei, as those in question, seems to be necessary in order to account for the results of the experiments on large angle scattering of the rays.
In an attempt, to explain some of the properties of matter on the basis of this atom-model we meet, however, with difficulties of a serious nature arising from the apparent instability of the system of electrons: difficulties purposely avoided in atom-models previously considered, for instance, in the one proposed by Sir J. J. Thomson. According to the theory of the latter the atom consists of a sphere of uniform positive electrification, inside which the electrons move in circular orbits.
The principal difference between the atom-models proposed by Thomson and Rutherford consists in the circumstance that the forces acting on the electrons in the atom-model of Thomson allow of certain configurations and motions of the electrons for which the system is in a stable equilibrium; such configurations, however, apparently do not exist for the second atom-model. The nature of the difference in question will perhaps be most clearly seen by noticing that among the quantities characterizing the first atom a quantity appears - the radius of the positive sphere - of dimensions of a length and of the same order of magnitude as the linear extension of the atom, while such a length does not appear among the quantities characterizing the second atom. viz. the charges and masses of the electrons and the positive nucleus; nor can it be determined solely by help of the latter quantities.
The way of considering a problem of this kind has, however, undergone essential alterations in recent years owing to the development of the theory of the energy radiation, and the direct affirmation of the new assumptions introduced in this theory, found by experiments on very different phenomena such as specific heats, photoelectric effect, Röntgen rays, etc. The result of the discussion of these questions seems to be a general acknowledgment of the inadequacy of the classical electrodynamics in describing the behaviour of systems of atomic size. Whatever the alteration in the laws of motion of the electron may be, it seems necessary to introduce in the laws in question a quantity foreign to the classical electrodynamics, i. e. Planck's constant, or as it often is called the elementary quantum of action. By the introduction of this quantity the question of the stable configuration of the electrons in the atoms is essentially changed, as this constant is of such dimensions and magnitude that it, together with the mass and charge of the particles, can determine a length of the order of magnitude required.
This paper is an attempt to show that the application of the above ideas to Rutherford's atom-model affords a basis for a theory of the constitution of Atoms. It will further be shown that from this theory we are led to a theory of the constitution of molecules.
In the present first part of the paper the mechanism of the binding of electrons by a positive nucleus is discussed in relation to Planck's theory. It will be shown that it is possible from the point of view taken to account in a simple way for the law of the line spectrum of hydrogen. Further, reasons are given for a principal hypothesis on which the considerations contained in the following parts are based.
I wish here to express my thanks to Prof. Rutherford for his kind and encouraging interest in this work.

Related references
See also
E. Rutherford, Phil. Mag. 21 (1911) 669;
E. Rutherford, Phil. Mag. 24 (1912) 453;
W. Ritz, Phys.Zeitschr. 9 (1908) 521;
N. Bohr, Phil. Mag. 25 (1913) 24;
J. W. Nicholson, Month. Not. Roy. Astr. Soc. 72 (1912) 729;
J. W. Nicholson, Month. Not. Roy. Astr. Soc. 72 (1912) 693;
J. J. Thomson, Phil. Mag. 7 (1904) 237;
M. Planck, Annalen der Physik. Leipzig 31 (1910) 758;
M. Planck, Annalen der Physik. Leipzig 37 (1912) 642;
A. Einstein, Annalen der Physik. Leipzig 17 (1905) 132;
A. Einstein, Annalen der Physik. Leipzig 20 (1906) 199;
A. Einstein, Annalen der Physik. Leipzig 22 (1907) 180;
J. W. Nicholson, Month. Not. Roy. Astr. Soc. 72 (1912) 49;
J. W. Nicholson, Month. Not. Roy. Astr. Soc. 72 (1912) 139;
J. W. Nicholson, Month. Not. Roy. Astr. Soc. 72 (1912) 677;
Analyse data from
E. C. Pickering, Astron. Journ. 5 (1897) 92;
E. C. Pickering, Astron. Journ. 4 (1896) 369;
F. Paschen, Annalen der Physik. Leipzig 27 (1908) 565;
A. Fowler, Month. Not. Astr. Soc. Dec., (1912) 73;
J. J. Thomson, Phil. Mag. 23 (1912) 456;

Reactions
  atom* atom p
  atom atom*

Particles studied
  atom mass, qn
  atom* mass, qn

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Invention of the quantum theory of atomic spectra based on the Rutherford model of atomic structure - Bohr's atom.
    
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