48 



CIIEMISTEY. 



thus, H-O-H, which is the same thing as H 2 O, only it shows the rel- 

 ative atomicity of its constituent elements. The atom-Jixiny power of 

 the elements is not a fixed quantity for each element; nitrogen, for 

 instance, may be pentatomic or triutomic ; sulphur may be hexatomic, 

 tetratomic, or even diatomic, according to circumstances ; the maximum is 

 generally taken as the true atomicity of the element. This variation is in- 

 geniously accounted for by supposing that in the lower powers the bonds 

 are neutralized by self-saturation, or by combining with themselves ; thus, 



if in pentatomic nitrogen, ^N^, two of the bonds unite, it may become 

 triatomic, ,N> The bonds are said to be saturated when joined to them- 



V X 



selves or to the bonds of some other element. 



It scarcely ever happens that an element possessing an even atomicity 

 can assume an odd atomicity, nor can the reverse take place, consequently 

 the elements are divided into two great classes those of even atomicity, 

 called artiads, and those of odd atomicity, called perissads. The following 

 table embraces all the commonly occurring elements which are thus grouped. 

 The symbols only are given, in order to familiarize you with them. This 

 whole subject of atomicity is a theory which is as yet only in its infancy, and 

 is so replete with exceptions to the rule that the longer it is studied the 

 more unsatisfactory it becomes. We have only sketched its fundamental 

 principles, and we do not propose to apply them in the body of this work, 

 notwithstanding they have been of great advantage to the progress of the- 

 oretical chemistry. 



In the following table the monatomic elements are called monads; the 

 triatomic, triads; the diatomic, dyads, etc., in accordance with custom. 



TABLE OF ATOMICITY. 



