﻿and the Theory of Atomic Structure. 563 



larger than the values given in the table. The last columns 

 give the differences : — 



A I = (La 1 +Ma 1 ) — L^ 7 and 



A 2 =L 1 -(La 1 + Ma 1 ). 



As may be seen from diagram IV., A : represents the energy 

 difference between the 5 and the N x level. For the ele- 

 ments with lower atomic number than Pb the N x level 

 appears to lie higher than the 5 level, the difference 

 between these levels increasing with decreasing atomic 

 number. As one unit of the frequency, i. <?., the Rydberg 

 number, corresponds to 13'45 volt, we may conclude that 

 for Lu, Er, and Dy the N x level lies about 45 volt higher 

 than the 5 level. 



A 2 represents the binding energy of the 4 4 electron (see 

 diagram IV.). The discontinuity appearing in the table for 

 the value of A 2 for W is not essential. Using the author's 

 value of /3 5 for L^ of this element, instead of Duane's and 

 Patterson's value for Lj, we get for W : A 2 = 2*42, a value 

 which agrees fairly well with the values for the other 

 elements standing in the table. It appears from the table 

 that it is most probable that for Dy the binding energy of 

 the 4 4 electron at least must be less than 20 volt, thus being 

 of about the same magnitude as the binding energy of the 

 valency electrons. 



As to the binding energy of the 5i electrons, we have to 

 consider two values : one corresponding to the 5 level and 

 one corresponding to the 4 level. As may be seen from the 

 table, the first value is at least more than 45 volts for Dy, 

 the second value is given approximately by the frequency 

 difference of the L 3 absorption-edge and the line L74. From 

 a discussion in Part III. § 8 it follows that the latter 

 difference is likely to be more than 25 volts for Dy. From 

 this we see that, where the 4 4 electrons appear for the first 

 time in the periodic table, they are more loosely bound than 

 the 5x electrons ; for the elements with higher atomic 

 number than Pb, however, the 4 4 electrons are definitely 

 bound more firmly than the 5! electrons. 



§ 3. It is of interest to consider other regions in the 

 periodic system where we might expect to meet with pheno- 

 mena analogous to those discussed in the last paragraph. In 

 the neighbourhood of the iron group the M-shell develops 

 from a shell containing four 3 X electrons and four 3 2 elec- 

 trons into a shell containing six 3j, six 3 2 , and six 3 3 electrons. 

 When the 3 3 electrons appear for the first time, some 

 electrons of the X-shell are already present. Numerical 



2 2 



