INFLUENCE OF INTRODUCED ELEMENTS n 3 



2. THE INFLUENCE ON ELEMENTS ALREADY PRESENT IN 

 A COMPOUND EXERTED BY ELEMENTS INTRODUCED. 



The influence which the introduced element exerts on 

 the behaviour of a compound is seen, in the first place, in 

 reactions which cause changes in the linkages of that 

 element : these have been considered in the previous para- 

 graphs. The introduction has, however, a further influence 

 which appears if in the molecule other linkages can be 

 broken, and in general this influence falls off with distance. 

 The influence is most clearly shown in the region of 

 organic chemistry, and may be brought under certain rules 

 though mostly only qualitative ; of these many are grouped 

 round the leading fact that an element communicates its 

 electro-affinity to the atomic group in which it appears, 

 and consequently raises or lowers its tendency to associate 

 with positive or negative electricity, with all the conse- 

 quences already described ; commonly the result of this is 

 a more or less marked positive or negative character in the 

 group. We will first deal with this point of leading im- 

 portance, which is to be traced essentially in the matter 

 of equilibrium, afterwards bringing together the further 

 specific influences which appear principally in changes of 

 velocity. 



A. Introduction of the Electro- affinity, i.e. of Positive 

 or Negative Character, into the Group into which 

 an Element enters. 



In the first place, since we are dealing essentially with 

 organic compounds, carbon is fairly indifferent towards 

 positive or negative electricity, i. e. it shows little tendency 

 to go into the ionic form. Hence the negative or positive 

 influence of associated elements is the more completely 

 felt. If this is negative it causes formation of positive 

 H-ions, i. e. of acid character, and reduces the tendency to 

 form negative OH-ions, i. e. basic character, but only, of 

 course, if hydrogen or hydroxyl is contained in the element 



H 



