101 



We point out that the nitrogen liere behaves as a tetia-vaieni 

 substance, the oxygen as a univalent one. 



Ammonia, in spite of its having 8 electrons in its outer shell, 



Fig. 3. 



A = phenyl, B = methyl, C = ethyl, D = oxygen. 

 Methyl ethyl phenyl ammonium oxide. 



can bind certain definite other atoms non-polarlj, provided there be 

 also an atom present that the electron, which is now in excess (and 

 is, therefore, expelled) can take up. 



This may also be expressed as follows: ammonia passes into the 

 positive ion condition when forming a bond with a hydrogen atom, 

 or in other words: ammonia can only receive a hydrogen io7i, as 

 it is saturated with electrons. Here the nitrogen does not become 

 tetra-valent, but penta-valent. This tifth valency, however, has 

 another character: it gives rise to a polar bond. 



It is this very power through which a 

 number of atoms, which to start with, have 

 an electro-negative character, acquire the pro- 

 perty of an alkali-metal ; we need only mention 

 iodine and sulphur. 



We may now apply these considerations to 

 the boron atom, and examine in the first place 

 what is the nature of the bonds in thesinifde 

 derivatives of this element. The halogen com- 

 pounds are the most suitable to decide this question. 



Fig. 4. 

 Ammoniumion. 



