﻿Distribution of Electrons in JSa and CI Atoms. 4IJ5 



accounted for this law, just as an illustration of the appli- 

 cation of the principle involved in considering spatial 

 distribution. 



A. H. Compton used the experimental results obtained by 

 W. H. Bragg in order to calculate the electron distribution. 

 W. H. Bragg showed that the intensity of reflexion is a 

 function of the angle of reflexion alone, when allowance has 

 been made for the arrangement of the atoms in the crystal, 

 and he determined the relative intensity of reflexion by a 

 number of planes in rock-salt and calcite. Compton cal- 

 culated from these values the relative amplitudes of the 

 waves scattered by the atoms in different directions, by 

 means of the reflexion formula of Darwin, and proceeded 

 to test various arrangements of electrons in order to find 

 one which gave a scattering curve agreeing with that found 

 experimentally. He supposed that the electrons were 

 rotating in rings, governed by Bohr quantum relationships 

 In sodium, for example, he placed four electrons on an 

 inner ring, six on the next ring, and a single valency electron 

 on an outer ring. In chlorine the rings contained four, six, 

 and seven electrons respectively. Compton found that these 

 atomic models gave a fair agreement with W. H. Bragg's 

 results. 



Debye and Scherrer came to the same conclusion as to the 

 significance of intensities as regards electron distribution 

 which was implied in W. H. Bragg's work and stated more 

 fully by Compton. They considered two interesting cases. 

 The first was that of the lithium fluoride crystal. They 

 compared the intensity of reflexion by planes where the 

 fluorine and lithium atoms reflected waves in phase with 

 each other, with that by planes where these atoms acted 

 in opposition to each other. The relative amplitudes at any 



TT -i- T i 

 angle for such planes may be expressed by the ratio ^ — ^> 



where F and Li are the amplitudes contributed by the fluorine 

 and lithium atoms respectively. Their figures indicated 



Ui r • 



that the limiting values of ^ — p at zero angle of scattering 



is 1*5, signifying that a valency electron has passed from the 



lithium to the fluorine atom I ^ =1*5 ). 



Their intensities of reflexion were measured by the 

 darkening of a photographic plate in the powder method 

 of analysis which these authors initiated. In view of the 



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