The Basis of Life 29 



Some elements found in biological materials are listed here : 



Name Symbol Atomic Number Atomic Weight 



Calcium Ca 20 40.08 



Carbon C 6 12.010 



Chlorine CI 17 35.457 



Copper Cu 29 63.54 



Hydrogen H 1 1.008 



Iodine I 53 126.92 



Iron Fe 26 55.85 



Magnesium ■. . . . Mg 12 24.32 



Nitrogen N 7 14.008 



Oxygen O 8 16.000 



Phosphorus P 15 30.98 



Potassium K 19 39.096 



Sodium Na 11 22.997 



Sulfur S 16 32.066 



When indicating a reaction between two elements, it is customary 

 to use abbreviations and to indicate by means of an arrow the direction 

 in which the reaction proceeds. For example, sodium chloride results 

 from the following reaction : 



Na + CI > NaCl 



In this example, one atom of sodium combined with one of chlorine. 

 When hydrogen and oxygen combine to produce w^ater, the proportions 

 of each are indicated thus : 



2 H + O > H.O 



The number of atoms involved must be indicated on both sides of the 

 equation and must balance. 



Salts, Acids, and Bases.— Many substances when placed in water 

 dissociate into their component parts. Thus the sodium and chlorine 

 of common table salt separate to become ions when salt is dissolved 

 in water. This is indicated as follows : 



NaCl > Na+ + Cl" 



The positive and negative signs indicate the electrical charge of the 

 ion. When materials dissociate in this manner, chemical reactions 

 take place more readily. 



