10 ELEMENTS OF BIOLOGY 



It is therefore very reactive with other atoms, and forms a very 

 great number of compounds. So great is the known number of 

 compounds of carbon that their study constitutes a separate branch 

 of chemistry, known as Organic Chemistry. The name is due to a 

 behef of chemists of more than a century ago that all carbon com- 

 pounds were formed solely in living organisms. Compounds that 

 do not contain carbon atoms are known as inorganic compounds. 

 For clarity it is convenient to represent the relation of carbon 

 atoms with other atoms in a compound by conventional diagrams, 

 commonly called structural formulae. All four of the unsatisfied 

 bonds of the carbon atoms may take up hydrogen atoms, as we 

 have seen how the oxygen atom holds two hydrogens in the water 

 molecule. The resulting carbon compound is written structurally 

 as: 



H 



I 

 H— C— H 



H 



This is the gas, methane, the chief component of natural gas. Or 

 one or more of these bonds may be taken by another carbon atom 

 with its hydrogen atoms and other types of atoms that may be 

 associated. Thus 



H H 



I I 

 H— C— C— OH 



H H 



is regarded as the arrangement of the atoms in common grain, or 

 ethyl, alcohol. Common cane sugar contains twelve carbon atoms 

 arranged in a similar fashion, the side bonds being satisfied by 

 twenty-two hydrogen and eleven oxygen atoms. The common way 



