Constitution and Stability of Atom Nuclei, 323 



usually associated tn pairs. This is not unlike the 

 relation found by Lewis for the planetary electrons in 

 molecules, since in only about one in a thousand molecules 

 is there an odd number of planetary electrons. A later 

 discussion will consider the relation of these pairs of nuclear 

 neo-ative electrons to the groups other than the alpha group 

 which seem to occur in the nucleus. The most prominent 

 of these groups seem to be those of formulas p s e 2 and p 2 e 2 , 

 where p stands for a proton, and e for a negative electron. 

 Both of these groups contain a single pair of negative 

 electrons, just as is the case with the alpha particle. These 

 groups may be written (p 3 e)e and (p 2 e)e. 



The rarity of atoms in which the number of negative 

 nuclear electrons is odd is well illustrated by the meteorites. 

 In no case does the average result of the quantitative analyses, 

 as represented by any collected set of data, indicate the 

 presence of any element whose most abundant isotope shows 

 an odd value for .N, and the only atomic species of this 

 class which seem to be present are Mg! 25 (1*64 per cent.), 

 and Six 29 (about 1*5 per cent.) which together make up 

 about 3 per cent, of the atoms of the material. Thus about 

 97 per cent, of the atoms have an even number for N. In 

 the earth's crust, only about one atom in 50 has an odd 

 value for N. 



Possibly the most beautiful illustration of the effects of 

 this tendency for N to be an even number is to be found in 

 the atomic weights of the most abundant atomic species in 

 each element of odd atomic number. When M is odd, since 

 P — N = M, it is evident that either P or 1ST, but not both, 

 must be odd, so if, according to rule, N is even, then P or 

 the atomic weight must be odd. Now it is very remarkable 

 that the atomic weights of all of the elements from 3 to 27 

 inclusive, with the exception of nitrogen, are odd numbers, 

 and the rule holds that P is odd for all of the individual 

 isotopes as well, with the exception of those, such as B 10 

 and Li 6 , which occur only in extremely small percentages. 

 The rule also holds for the isotopes found by Aston, Br 9 7 9 , 

 Br n 81 , As 9 75 , I 21 127 , Clj 35 , Cl 3 37 , and possibly a 01 5 39 . 



The above equation also indicates that when the atomic 

 number (M) is even, P should also be even if N is to be 

 even, so the atomic weights of atoms of this set should 

 be even, as is true for nearly all the light atoms, especially 

 for the most abundant isotope. It is also true for both the 

 uranium and thorium radioactive series, and for five of the 

 six isotopes of krypton. 



Z2 



