the Molecule and Chemical Combination. 539 



products of dissociation of a complex molecule were a simpler 

 molecule, we might get this with a double charge. Thus if 

 a molecule of 00 2 , for example,, were to dissociate by an 

 octet round one of the oxygen atoms breaking away from 

 the system, the atoms C and with 8 electrons would be 

 left behind ; as the positive charges on the atoms amount to 

 10 units, the molecule of CO formed in this way would have 

 a double charge. As a matter of fact, CO is one of the 

 few doubly charged molecules I have found in the positive 

 rays. 



Let us now turn to the negatively electrified atoms. These 

 have had an extra electron added to the outer layer ; but if a 

 cell of eight is the maximum number consistent with stability, 

 it is clear that an atom such as one of neon or argon, which 

 already contains 8 in the outer layer, is not in a condition to 

 receive another electron and so cannot be negatively charged. 

 This is borne out by observations on the positive rays, for 

 we never find the atoms of these elements occurring with a 

 negative charge. Again, we have supposed that in molecules, 

 when the number of electrons is sufficient, the electrons are 

 arranged in a series of cells of 8 ; since each cell is a satu- 

 rated system, there is no place for an electron to find a 

 resting-place and so no possibility of the molecule acquiring 

 a negative charge. We find this borne out by the positive 

 rays : a negatively electrified molecule is exceptional, though 

 there are cases like those of oxygen and unsaturated hydro- 

 carbons where the molecule can acquire a negative charge. 



The molecules which can receive a negative charge are, I 

 think, those consisting of a pair or more of cells which have 

 more than two electrons in common. Let us take, for example, 

 the molecule of oxygen : we have regarded this as consisting 

 of two cells with four electrons in common ; as long as this 

 contact is intact, neither cell can receive an electron without 

 losing its stability by containing more than 8 electrons. 

 Suppose, now, that the contact were to open out so that the 

 cells had only two electrons in common ; there would now 

 be room on each cell for an electron without the number on 

 either cell exceeding 8, so that this molecule might receive 

 one or even two negative charges. Compare this case with 

 that of a molecule of chlorine, where the two cells have only 

 two electrons in common : it cannot receive an electron while 

 the contact is intact, and any loosening of the contact would 

 lead to a separation of the atoms ; hence w r e should anticipate 

 that while a molecule of oxygen could acquire a negative 

 charge, one of chlorine could not. A molecule in which none 

 of the cells have more than tw^o electrons in common is one 



