420 Wells — Chromophore Grouping of Atoms 



black color of the magnetic oxide of iron may be supposed 

 to be due to the effect of this grouping upon the color 

 of the combined red and so-called grey ferric and ferrous 

 oxides. 



The chromophore grouping that has been presented 

 here is a very curious thing. In the cases of Au'-Au'" 

 and Sb'"-Sb v there is a difference of two units of valency, 

 while with Fe"-Fe'" and Cu'-Cu" there is a difference of 

 only one unit, and, furthermore, these four pairs of valen- 

 cies are all different. It is particularly remarkable that 

 the three chlorides, CsCl, SbCl 3 and SbCl 5 which consti- 

 tute one of the examples of the chromophore grouping 

 are all of them colorless compounds. 



It seems possible that the action of this chromophore 

 may be explained by exchanges of negative electrons 

 between the atoms that differ in valency. It is supposed 

 that in passing from one valency to another an atom 

 gives up or takes on one or more electrons, and if it is 

 assumed that the atoms of a metal in two states of valency 

 in the same molecule, instead of retaining fixed individual 

 valencies, continually make these exchanges of electrons, 

 it may be supposed that light, passing through such mole- 

 cules, is in some way affected, so that colors or opacity 

 are produced. 



The hypothesis of spontaneous electronic activity that 

 has been advanced to explain the behavior of the chromo- 

 phore grouping may be applied as a general cause of 

 color. It may be supposed that certain atoms, occurring 

 in such combinations that their structures are labile, may 

 be continually exchanging electrons with neighboring 

 atoms even when atoms of an element in two states of 

 valency are not present. 



This supposition seems plausible, since it might be 

 expected that unless the activity of the electrons was 

 spontaneous it would not take place at all in bringing 

 about chemical combinations and changes in valency. 



The common occurrence between atoms of spontaneous 

 electronic exchanges, of sufficient intensity to affect the 

 passage of light is the theory advanced here to explain 

 colors. A strong argument in its favor is the fact that 

 a very large proportion of the elements that give at least 

 one colored salt, ion, or oxide are those that occur in more 

 than one condition of valency and whose atoms, conse- 



