196 SMITH'S INTERMEDIATE CHEMISTRY 



can be effected much more readily, and extensive ionization may 

 result. 



A positive ion, therefore, is a. frftft fl.t,nm r or grrpup of ato, w*"^ 

 bfli 8 ! lfi* f QT1 ^"*+j or a. number of plfintrnna T such as Na+. 

 (NH 4 )+, Zn++. A negative ion is a free atom, or group of atoms. 

 whip,h hflfi fnf'flfrf nn ^VfltroBj orjar-number of electrons, such as 

 C1-, (NO,)-, S". 



Some Possible Misunderstandings. Before we close the 

 chapter, it will be profitable to anticipate some difficulties into 

 which the reader may fall. If the ionic hypothesis is not properly 

 understood, it appears to conflict so strongly with what the stu- 

 dent has learnt in previous chapters that he is apt to become 

 hopelessly confused. The following points of possible misunder- 

 standing and the explanations appended should therefore be read 

 through very carefully. For convenience of illustration, sodium 

 chloride is taken as a typical electrolyte in the questions and 

 answers listed below. The student should test his knowledge of 

 the subject by substituting other electrolytes. 



1. If sodium chloride is broken up in aqueous solution into 

 sodium and chlorine, why do we not find any of the properties of 

 sodium or of chlorine exhibited by the solution? This has always 

 been a very common misapprehension of the ionic theory. Many 

 prominent chemists never could understand how sodium (a metal 

 which acts vigorously on water) and chlorine (an obnoxious gas) 

 could exist side by side in a solution of sodium chloride without 

 immediately notifying us of their presence by characteristic 

 reactions. The answer is that free sodium and free chlorine do 

 not exist in sodium chloride solution. The ionic hypothesis has 

 never stated that they do. What it does state is that sodium 

 ion Na + and chloride ion Cl~ are present in the solution. These 

 are entirely different substances from atomic sodium Na and mol- 

 ecular chlorine Cl2. The electric charges on the ions change 

 their properties completely. There is no more reason why they 

 should behave like free sodium and free chlorine than there is 



