MERCUROUS CHLORIDE BY HAROLD S. KING 117 



forms have different electron structures; — 2.8.18 for the cup- 

 rous ion and 2.8.17 for the cupric. From the above electron 

 structure for mercury, one would predict, a priori^ that if mer- 

 cury could exist with any valence other than two, the trivalent 

 would be more stable than the monovalent form. 



The evidence is so much in favor of the formula Hg.Clj for 

 mercurous chloride, that in this paper it will be used in pre- 

 ference to the simpler form. 



The next point to consider is how these four atoms may be 

 combined in the molecule. The structural formula for HgjCU 

 is universally represented as Cl-Hg-Hg-Cl. This might be 

 written according to the Lewis-Langmuir hypothesis as 

 :Cl:Hg:Hg:Cl: where each chlorine has completed its octet 

 leaving the two mercury atoms held together by a single 

 electron pair. However a radically different structure ex 

 plains the properties of mercurous chloride more satisfactorily 

 It is well known that mercuric compounds easily form complex 

 ions such as HgCl^Hgl^ etc. It seems that the mercuric 

 ion is capable of attracting to itself four groups. By sharing 

 an electron pair with each of these groups, it completes an 

 additional octet about the mercury kernel. When chlorine 

 acts on an excess of metallic mercury, the primary reaction 

 is probably \lg-\-C\i = YigCV . Then the mercuric chloride 

 reacts with metallic mercury to give mercurous chloride: 

 HgCL+Hg = Hg,CL. It is quite possible that the atom of 

 metallic mercury first loses its two valence electrons to the 

 mercuric chloride molecule and then shares an additional pair 

 of electrons from the outer shell of its kernel to give a compound 

 containing a mercury ion surrounded by an additional octet as 



in Hg:Hg:Cl, which can be represented by the non-electronic 

 CI 



formula Hg = HgCl2. This structure is substantiated by the 

 fact that calomel dissociates so easily. If mercurous chloride 

 be exposed to light, it soon turns dark due to. the formation of 

 free mercury. It is a common phenomenon for light toMoosen 



