Peculiar Properties of Water 95 



will acquire under a given set of conditions. The following ideas have 

 been worked out during the past three years at Purdue University in 

 a seminar course for graduate students. 



The ideas contained herein are an extension of the Lewis-Langmuir 

 theory of atomic structure which has already proved so fruitful.^ For 

 the topic under consideration, we need to consider only some of the ele- 

 ments in the first two periods. 



Let us consider the simplest hydrocarbon and the hydrogen com- 

 pounds of nitrogen and oxygen. Methane, CH,, with a molecular weight 

 of 16 and a very small external field of force is characterized, in addi- 

 tion to its chemical inertia, by a low boiling point, 160° C. Ammonia 

 is NHi (figure 3). The nitrogen atom has completed its octet by join- 

 ing on three hydrogens, each with a single electron. These are probably 

 placed at three of the corners of a tetrahedron. But there is a pair 

 of electrons left over which gives that part of the molecule a negative 

 character. Corresponding to this, one or more of the hydrogens will 

 have a slight positive character; that is, the electrons will be shifted 

 a bit from one or more hydrogens toward the central nitrogen. This 

 results in giving a certain "polarity" to the molecule. Such a polar 

 molecule ought to have much more attraction for other NH- molecules 

 than corresponds to its molecular weight, 17. As a matter of fact it 

 boils at — 33.5° which is an increase of nearly 130° over methane, 

 although there is an increase in molecular weight of but one. Liquid 

 ammonia is known to be associated. This association gives it a high 

 specific heat and high latent heat of vaporization because considerable 

 energy is used up in separating the complexes that result from these 

 polar attractions. 



Chemically, ammonia is very interesting. Bring it into contact 

 with a very polar substance like hydrogen chloride gas. The hydrogen 

 in that compound, as we have seen, is charged positively. When this 

 molecule comes in contact with ammonia the positively charged hydrogen 

 is attracted by the pair of electrons which make that part of ammonia 

 negative (figure 4) . This gives a methane-like structure to the am- 

 monium ion which, of course, now bears as a whole the positive charge 

 it picked up with the hydrogen. Then the chloride ion is held by electro- 

 static forces just as in sodium chloride. Nitrogen forms a great variety 

 of organic compounds and this property of polarity and of adding on a 

 positively charged hydrogen is found there also. This accounts for 

 the formation of such compounds as aniline hydrochloride and the 

 alkaloid complexes with different acids. Incidentally, such addition of 

 polar acid will increase the polarity of the organic compound with 

 important results which will be leferred to when we study solutions. 

 Certain metallic ions like silver, copper, cobalt, platinum, etc., due to 

 their structure, have the ability, like a hydrogen ion, of sharing that 

 extra pair of electrons in the ammonia molecule. The result is the 

 possibility of the preparation of an almost bewildering series of ammonia 

 compounds such as the cobaltammines. These are the "higher order 

 compounds" of Werner. 



1 Lewis. J. Am. Chem. Soc, 38, 762 (1916). Langmuir. ibid., H, 1543 (1919). 

 Science, 5J,, 59 (1921). 



