390 



Table 498. 

 X-RAY SPECTRA AND ATOMIC NUMBERS- 



Kaye has shown that an clement excited by sufficiently rapid cathode rays emits Rontgen rays characteristic of 

 that substance. These were analyzed and the wave-lengths determined by Moseley (Phil. Mag. 27, 703, 1914), using 

 a crystal of potassium ferrocyanide as a grating. He noted the K series, showing two lines, and the L series with several. 

 He found that every element from Al to Au was characterized by integer A^, which determines its X-ray spectrum; 

 N is identified with the number of positive units associated with its atomic nucleus. The order of these atomic num- 

 bers (iV) is that of the atomic weights, except where the latter disagrees with the order of the chemical properties. 

 Known elements now correspond with all the numbers between i and 92 except 6. There are here six possible elements 

 still to be discovered (atomic nos. 43, 61, 72, 75, 85). 



The frequency of any line in an X-ray spectrum is approximately proportional to A{N — 6)', where A and 6 are 

 constants. All X-ray spectra of each series are similar in structure, differing only in wave-lengths. Qj^ = (f/loo); 

 Q^ = (o/j'jto) where ti is the frequency of the a line and vo the fundamental Rydberg frequency. The atomic number 

 for the K series = Qk+ i and for the L series, Q^, + 7-4 approximately, w = 329 X 10" 



Moseley's work has been extended, and the following tables indicate the present (1919) knowledge of the X-ray 

 spectra. 



(a) K Series (Wave-lengths, X X 10' cm). 



Smithsonian Tables. 



