78 WHAT IS LIFE 



ments form a definite and limited series. This is 

 the series that properly appropriates the term 

 "matter." 



3. The series of the elements is determined by the 

 constitution of the nucleus of the atoms. 



The atomic number of the elements is determined 

 by the number of free unit charges on the nucleus 

 of the atom; but the number of free unit charges 

 (outer, or orbit, electrons) that an atom can carry 

 is, of course, determined by the constitution of the 

 nucleus of the atom. Thus at once it appears that 

 the nucleus of the atom determines the atom and all 

 its properties. Change in the nucleus of the atom — 

 ejection of alpha particles (helium atoms) or of 

 beta particles (negative electrons) in radioactivity, 

 changes the element. An alpha-ray transformation 

 changes the place of the atom in the periodic table 

 by two units to the left and reduces its weight by 

 four units. A beta-ray transformation, on the 

 other hand, raises the element one unit to the right, 

 without any noticeable change in atomic weight. 

 (Soddy, Fajans.) It is not questioned today that it 

 is the nucleus of the atom that determines the 

 element. 



4. The ninety-two atoms, the ninety-two ele- 

 ments, are the building-blocks out of which the entire 

 world of matter is composed. 



