60 life's beginning on the earth 



house, and that the arrangement of the atoms determines 

 the properties of a carbon compound. The same bricks may 

 be laid to turn out either a beautiful colonial mansion or a 

 shabby tenement. Only by varying the structure would it 

 be possible to obtain such an enormous variety of sub- 

 stances — 300,000 different compounds, from only four 

 constituents. The carbon atom has the rare property of 

 holding large structures together; only the carbon atom can 

 serve as a building stone in nature for these immensely 

 diversified substances through which life in all its com- 

 plexity is possible. 



In order to appreciate fully this rare property, let us com- 

 pare all the known compounds which exclusively contain 

 oxygen and hydrogen, with those containing nothing but 

 carbon and hydrogen. There are only two oxygen-hydro- 

 gen compounds known. 



1. Water, in which hydrogen and oxygen atoms are 



linked like this: 



H— O— H 



2. Hydrogen peroxide in which the linkage is like this: 



H— O— O— H 



The last one is unstable since a linkage of two oxygen 

 atoms is readily broken. Other compounds such as 

 H — O — O — O — H, or chain systems with more oxygen atoms 

 are impossible. 



Compare this short list with that of all the known com- 

 pounds of carbon and hydrogen. So many are known that 

 only a few selected ones can be discussed. The simplest 

 one is methane, one of the gases contained in natural gas; 

 its molecule contains one carbon and four hydrogen atoms 



arranged as follows: 



H 



I 

 H— C— H 



I 

 H 



