J02 



Tliese liave BX, as constitution and entirely possess the character 

 of acid ciilorides, and not of salts. The three electrons are, accord- 

 ingly, not ceded, as even the fluorinm atoms are non-polarly bound. 



In these compounds boron has only six electrons in the outer 

 shell; in some respects they will, therefore, have an unsaturated 

 character (Fig;. 5). These halogen compounds can, indeed, become 

 saturated in two ways. 



The first way, which has been known longest and has already 

 been explained by Werner to a certain extent, refers to the adoption 

 of a molecule IIF. Then tiiere is formed e. g. HBF^, a mono-basic 

 acid. It may now be assumed thai a fourth atom F becomes non- 

 polarly bound, which, however, is not possible, as boron has no 

 free electron left, unless at the same time an electron (of the H) is 

 taken up, and conse(piently the group BF^ passes into the negative 

 ion-condition (Fig. 6). 



Fig. 5. 

 Borium fluoride. 



Fig. 6. 

 Borium fluor hydrogenic acid. 



It may also be said that the polarly-bound HF-molecule enters the 

 shell of the boron with two of the electrons of the fluorium atom, 

 the whole BF, -group becoming a negative ion. 



For the H-ion it is entirely immaterial whether the ceded electron 

 is attached to one of the four tluoriuni-atoms outside or inside the 

 shell of the boron ; as ion it has no fixed place in the molecule, 

 and can wander all round the complex. 



In view of the mono-valency of tluorium and of the complex, 

 boron maj' be assumed (o be penta-valent with as much reason as 

 the nitrogen in ammonium compounds. 



The second way in which boron fluoride can add to its electrons 

 is; to combine with molecules of which there are two electrons 



