113 



S-term ;? = 2 is to be put instead of ;! = 1. Schrödinger has come to the same 

 conclusion by means of the assumption that, in the stationary stales corresponding 

 to the S-terms of the sodium spectrum, we have to do with a molion of the series 

 electron in which during each revolution the electron gets inlo the region of liie 

 inner electron orbits'), and that therefore the quantum number n in none of these 

 states can be less than 2. The significance of this fact was at the same time pointed 

 out by the writer") in connection with the general considerations on the structure 

 and stabihty of atoms mentioned in the note to § 2. As has been pointed out in 

 Essay III, these considerations lead to the assumption that an essential change in 

 the quantum numbers entering into the classification of the spectral terms is to be 

 introduced. While it will be clear from the apphcation of the correspondence prin- 

 ciple given in the text, that the values of the quantum number designated by r are 

 to be kept unaltered, it is shown that for instance in the spectra of the alkali 

 metals the values for the main quantum number n, given in the diagram on page 103 

 can onl}^ be maintained for the series of terms corresponding to t equal to or larger 

 than 3. The first S-term in these spectra will correspond to an orbit of the series 

 electron, whose main quantum number increases by one unit, if we advance in the 

 periodic system to the next group of elements. Thus for this orbit we have in 

 lithium n = 2, in sodium n = 3 etc. A corresponding change is also to be introduced 

 in the main quantum numbers corresponding to the P-terms in these spectra. While, 

 as in the diagram on page 103, in lithium the first P-term is to be characterized 

 by ;i = 2, this term in sodium corresponds to n =■ 3, in potassium to ;? = 4 etc. 



Note to § 2. The considerations given in this paragraph can not in the details 

 be maintained in the present state of atomic investigation. In fact, several of these 

 considerations are especially fitted to emphasize the chief difficulties mentioned in 

 in the introductory note to Part III (p. 101). This refers particularly to the remarks 

 concerning the stability of electronic orbits in atoms. However, we shall find that 

 certain general statements concerning the change of series spectra of different order 

 with increasing atomic number are essentially adequate. Thus it will be seen, that 

 the remarks touching on this point are, in content, equivalent to the laws designated 

 as the "spectroscopic displacement theorem" by Sommerfeld and Kossel in their 

 above mentioned paper, which have proved themselves very fruitful for the classi- 

 fication of the spectra as is shown in Sommerfeld's book. Already concerning this 

 point the later investigations on atomic structure, however, have led to the con- 

 clusion, that deviations from the laws in question are to be expected in the later 

 periods of the periodic system, in that here with increasing atomic number we have 

 to do not always with a repetition of the configuration of the inner electron system 

 with an equal number of electrons, but, as pointed out in Essay III, we meet in 



') E Schrödinger, Zeitschr. für Phys. 4, p. 347 (1921). 



") Cf. "Nature", Vol. 107, p. 104 and Vol. 108, p. 208 (1921). 



