THE VALENCE OF NITROGEN IN AMMONIUM SALTS. 



By WILLIAM A. NOYES and RALPH S. POTTER. 



(Read April 24, 1914.) 



During the early years of the development of the theory of 

 valence many chemists held the view that each element has an un- 

 varying valence. The apparent change of valence in nitrogen from 

 ammonia to ammonium salts and in phosphorus from phosphorus 

 trichloride to phosp'horus pentachloride was explained by calling the 

 ammonium salts and the pentachloride molecular compounds, as dis- 

 tinguished from ammonia and the trichloride, in which the true 

 valence of the elements was supposed to be shown. This view 

 received support from the dissociation of ammonium salts and of 

 phosphorus pentachloride in the gaseous state. Gradually, with the 

 demonstration that phosphorus pentachloride volatilizes in part .un- 

 changed, that phosphorus pentafluoride, PFg, has a vapor density 

 corresponding to its formula and, in general, that dissociation in the 

 gaseous state does not correspond to any rational distinction between 

 unitary and molecular compounds the view that elements may show 

 a varying valence in their compounds and that nitrogen and phos- 

 phorus are sometimes trivalent and sometimes quinquivalent, came 

 to be generally accepted. 



More recently Werner^ has proposed a modified molecular 

 formula for ammonium chloride, H3N..HCI. By this formula he 

 intends to indicate that in the ammonium salts the nitrogen atom 

 retains a normal valence of three but that the nitrogen atom of the 

 ammonia and the hydrogen atom of the ^hydrochloric acid are held 

 together by secondary ("Neben") valences, the hydrogen and 

 chlorine of the acid retaining essentially the same relation to each 

 other as in the free acid. 



^See "Neuere Anschauungen auf dem Gebiet der anorganischen Chemie," 

 p. 96 (1905). 



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