36 THE CHEMISTRY OF LIFE 



grees centigrade. The center of a hydrogen bomb at the time of ex- 

 plosion reaches a temperature up in the millions of degrees. 



All of this movement of molecules may seem fantastic, but it can be 

 demonstrated rather easily in the zoology laboratory. If we suspend 

 any very small particles — bacteria, fine soil, etc. — in water and view 

 them under the high power of the microscope, these particles will be 

 seen to move. They move back and forth rapidly in different directions. 

 Such movement is known as Brownian movement. Where does the 

 energy of such movements come from? It is the movement of the 

 molecules of water which bombard these small particles on all sides. 

 The molecules are much too small to be seen, but as they hit the sus- 

 pended particles with great force they can cause movement of the 

 particles. It is probably not a single molecular hit which causes move- 

 ment in any direction, but a brief unbalance of hits from different sides. 

 If more molecules hit the particle from one side than another, then the 

 particle will be driven away from the side of greatest hits. We can 

 often see Brownian movement of small particles inside of living cells 

 when viewed under the microscope. 



Divisions of Matter 



All of the matter of the universe may be divided into elements, 

 compounds, and mixtures. An element is a variety of matter that 

 cannot be broken down into two or more different kinds of atoms. 

 Iron, sulfur, oxygen, hydrogen, iodine, and calcium are typical examples 

 of chemical elements. When any of these substances are broken down 

 into the smallest divisible unit which retains the characteristics of the 

 elements we find only one kind of atom. Compounds, on the other 

 hand, are formed by a combination of two or more elements which are 

 chemically united. Water, for instance, is a compound because it is 

 formed from two elements — hydrogen and oxygen. By proper chem- 

 ical techniques water can be broken down into these two component 

 elements. The smallest divisible unit of a compound is known as a 

 molecule. Water, therefore, is formed of molecules, and each molecule 

 of water is composed of two atoms of hydrogen and one atom of 

 oxygen. It is designated chemically as H,0 or HOH. All compounds 

 are formed from molecules, but there are some cases where molecules 

 do not form compounds. Oxygen, as it exists in an oxygen tank in the 

 hospital, for instance, is an element, but it is composed of molecules. 

 When oxygen exists in this pure state the atoms always unite in pairs 

 to form molecules of oxygen composed of two atoms. Hence, we 

 represent the oxygen as CX. Since there is only one kind of atom 



