56 



SCIENCE PROGRESS 



the compounds NH, NHa, NH4, and NHg cannot exist, since 

 in these cases we find p = i, \,-\ and - i respectively, instead 

 of zero, as it must be for a single octet. For the oxides we see 

 from (ii) that if p is to be an integer, e must always be even. 

 Since nitrogen has 5 available electrons and oxygen 6, 

 there must always be an odd number of electrons unless the 

 number of nitrogen atoms is even. This gives NjO, as the 

 simplest general formula for the nitrogen oxides. 



When X = i the theory indicates the structure N = O = N 

 or N = N =0, where each valence link represents the sharing 

 of a pair of electrons. The extraordinary fact immediately 

 appears that the internal arrangement of such a substance 

 should be almost exactly like that of carbon dioxide. Both 

 molecules are represented by three cubes side by side in a 

 row. CO2 has a carbon atom with a charge on the nucleus of 

 4 positive units, while the two oxygen nuclei have 6 positive 

 units, making a total positive charge of 16. NjO has two 

 nitrogen atoms each with 5 positive charges, and one oxygen 

 atom with 6 positive units, the total being 16 as with COj. 

 In both cases the nuclei are surrounded by completed octets, 

 giving a small external field which must be very similar for 

 both molecules. If the theory is correct the physical properties 

 of these two gases should be almost identical. The following 

 table shows how remarkable is this agreement : 



Critical temperature 

 Critical pressure 

 SolubHity in H2O at 0° C. 

 Solubility in EtOH at 15° C. 

 Density of liquid at - 20° C. 

 Density of liquid at - 10° C. 

 Viscosity at 20° C. . 

 Heat conductivity at 100° C. 

 Refractive index fXo at 16° C. 

 Dielectric constant of liquid at 0° C 

 Magnetic susceptibility of gas at 40 

 atmos. 16° C. . . . . 



-°C. 



CO2 



31-9' 

 77 atmos. 

 1780 



3-13 

 I-03I 



0-858 



148 X IO~' 



0'05o6 



1-190 



1-582 



0-I2 X ID 



-8 



N2O 



35-4° C. 

 75 atmos. 



1-305 



3-25 

 0-996 



0-856 



148 X 10-^ 



0-0506 



I -193 

 1-598 



0-I2 X I0~^ 



Both gases form hydrates with six molecules of water. The 

 vapour pre^i^ice of N20-6H20 is 5 atmospheres at 6° C, while 

 the other nj^lN^te has the same vapour pressure at 15° lower. 



The surface tension of liquid N2O is 2-9 — — ^ at i2'2°C., while 



CO3 has the same surface tension at 9-0° C. The power of the 

 new theory is strikingly illustrated by its indication of such 

 extraordinary relationships between compounds the properties 

 of which have been known, though uncorrelated, for so many 

 years. 



