Supplement to '' JVatttre,'" July 7, 1923 



41 



same character as that surrounding the hydrogen 

 nucleus — be much greater than for an electron in a 

 hydrogen atom that moves in an orbit with the same 

 principal quantum number, the maximum distance 

 of the electron from the nucleus at the same time 

 being considerably less than in such a hydrogen orbit. 

 As we shall see, this feature of the binding process 

 in atoms with many electrons is of essential importance 

 in order to understand the characteristic periodic 

 way in which many properties of the elements as 

 displayed in the natural system vary with the atomic 

 number. 



In the accompanying table (Fig. 9) is given a 

 summary of the results concerning the structure of 



Fig. 9. 



the atoms of the elements to which the author has 

 been led by a consideration of successive capture and 

 binding of electrons to the atomic nucleus. The 

 figures before the different elements are the atomic 

 numbers, which give the total number of electrons 

 in the neutral atom. The figures in the different 

 columns give the number of electrons in orbits corre- 

 sponding to the values of the principal and subordinate 

 quantum numbers standing at the top. In accordance 

 with ordinary usage we will, for the sake of brevity. 



designate an orbit with principal quantum number n 

 as an ^-quantum orbit. The first electron bound in 

 each atom moves in an orbit that corresponds to the 

 normal state of the hydrogen atom with quantum 

 symbol ij. In the hydrogen atom there is of course 

 only one electron ; but we must assume that in the 

 atoms of other elements the next electron also will 

 be bound in such a i-quantum orbit of type i^. As 

 the table shows, the following electrons are bound 

 in 2-quantum orbits. To begin with, the binding 

 will result in a 2^ orbit, but later electrons will be 

 bound in 2^ orbits, until, after binding the first 10 

 electrons in the atom, we reach a closed configuration 

 of the 2-quantum orbits in which we assume there 

 are four orbits of each type. This configuration is 

 met for the first time in the neutral neon atom, which 

 forms the conclusion of the second period in the 

 system of the elements. When we proceed in this 

 system, the following electrons are bound in 3-quantum 

 orbits, until, after the conclusion of the third period 

 of the system, we encounter for the first time, in 

 elements of the fourth period, electrons in 4-quantum 

 orbits, and so on. 



This picture of atomic structure contains many 

 features that were brought forward by the work of 

 earlier investigators. Thus the attempt to interpret 

 the relations between the elements in the natural 

 system by the assumption of a division of the electrons 

 into groups goes as far back as the work of J. J. 

 Thomson in 1904. Later, this view-point was developed 

 chiefly by Kossel (1916), who, moreover, has connected 

 such a grouping with the laws that investigations of 

 X-ray spectra have brought to light. 



Also G. R. Lewis and I. Langmuir have sought to 

 account for the relations between the properties of the 

 elements on the basis of a grouping inside the atom. 

 These investigators, however, assumed that the 

 electrons do not move about the nucleus, but occupy 

 positions of equihbrium. In this way, though, no 

 closer relation can be reached between the properties 

 of the elements and the experimental results concern- 

 ing the constituents of the atoms. Statical positions 

 of equilibrium for the electrons are in fact not possible 

 in cases in which the forces between the electrons 

 and the nucleus even approximately obey the laws 

 that hold for the attractions and repulsions between 

 electrical charges. 



The possibility of an interpretation of the properties 

 of the elements on the basis of these latter laws is 

 quite characteristic for the picture of atomic structure 

 developed by means of the quantum theory. As 

 regards this picture, the idea of connecting the group- 

 ing with a classification of electron orbits according 

 to increasing quantum numbers was suggested by 

 Moseley's discovery of the laws of X-ray spectra, and 

 by Sommerfeld's work on the fine structure of these 

 spectra. This has been principally emphasised by 

 Vegard, who some years ago in connexion with investi- 

 gations of X-ray spectra proposed a grouping of 

 electrons in the atoms of the elements, which in many 

 ways shows a likeness to that which is given in the 

 above table. 



A satisfactory basis for the further development of 

 this picture of atomic structure has, however, only 

 recently been created by the study of the binding 



