500 



Table 607 

 SECOND IONIZATION POTENTIALS OF THE ELEMENTS 



(Russell, Astrophys. Journ., 70, 1929, Mt. Wilson Contr. 383.) 

 (Continued from previous page) 



The general character of the spectra of most of the heavier elements can be deduced 

 from Tables 604 and 605. For the 2nd long period (Rb-Xe) the ionization potentials are 

 nearly the same as for homologous elements in the first, but average a little lower. The same 

 is true, in general, regarding the other energy levels, so that the arc and spark spectra of 

 these elements show high- and low-excitation lines in the same regions for those of the first 

 long period, but on the whole, a little farther to the red. 



At the start of the next period, we find the lowest-known ionization potentials (Cs and 

 Ba + for the second stage), which remain lower than in other periods until the rare-earth 

 group begins. In these elements the outer electrons are two 6s, one 5d, and from one to 14 

 4f electrons, the ionization potential slowly rising as the 4f group is built up. For the earlier 

 members, the lines of the ionized atom are the main features of the arc spectrum; those of 

 the neutral atom are best brought out in the furnace; first ionization potentials are very low. 

 The strong lines of the first spark spectrum shift towards the violet with increasing atomic 

 numbers, practically proving that the second ionization potential also increases. The number 

 of atomic-energy states should be much greater among the rare earths than for other ele- 

 ments. Their spectra are very intricate. 



The shell of 4f electrons completed, the ionization potential ceases to have any important 

 effect on the properties of the elements; note their chemical behavior and what is known of 

 their spectra (Hf+,W). A considerable fall in the ionization potential should occur between 

 the last rare earth, Lu, and Hf, and a gradual rise to Au and Hg. For Au and Hg ionization 

 is more difficult than for the homologous elements in the preceding periods. 



Second Ionization Potentials 



Smithsonian Tables 



