38 



THE CHEMISTRY OF LIFE 



the rather recent past when it was thought that the atom was the 

 smallest divisible unit of matter. Today we know all too well that the 

 atom can be split with a tremendous release of energy. In spite of 

 the great diversity of elements and compounds which are formed by 

 atoms, all atoms have the same basic units in their composition. The 

 variation comes from differences in the number of these units in the 

 atom and the arrangement of these units. 



The building materials of which atoms are constructed are mainly 

 protons, electrons, and neutrons. Let us take a very simple atom, hy- 

 drogen, and show how these parts are combined to produce it in ac- 



Fig. 3.2. Diagram of some simple atoms according to the generally accepted theory 

 of atom structure. H, hydrogen, the simplest of the atoms with a single proton and a 

 single electron. D, deuterium or heavy hydrogen, has an added neutron in its nucleus. 

 He, helium, with two each of protons, neutrons, and electrons. C, carbon, a more 

 complex atom with six each of protons, neutrons, and electrons. The carbon atom is 



drawn to a reduced scale. 



cordance with the generally accepted theory of Bohr. In the center of 

 this atom there is a nucleus consisting of one proton which carries a 

 positive charge. Then, in an orbit moving around this nucleus there 

 is an electron which carries a negative charge. There is another atom 

 which also has one proton in its nucleus and one electron in its orbit, 

 but it is heavier than hydrogen (about twice as heavy). We have 

 recently learned that this is because the nucleus of this atom (deuterium 

 or heavy hydrogen) contains a neutron which is neutral in its electrical 

 charge, as well as the positive proton. Thus, neutrons add weight to 

 atoms without affecting the charge. A carbon atom is somewhat more 



