the Molecule and Chemical Combination. 541 



the opening of the contact would probably result in the dis- 

 ruption of the molecule into a negatively electrified chlorine 

 atom and a neutral one, so that the electron would be attached 

 to a chlorine atom and not to a chlorine molecule. Similar 

 considerations will apply to more complicated molecules, and 

 we are led to the conclusion that when the molecule of the 

 gas contains two or more octets having electrons in common, 

 the electron may be caught by the gas and its mobility 

 reduced. If the molecule contains the "double bonds" of 

 the chemists, i. e. if two or more octets have 4 electrons in 

 common, the electron will attach itself to the molecule of the 

 gas. If there are only single bonds in the molecule the 

 molecule will be dissociated by the electron and the electron 

 will be attached to one of the products of dissociation. 



If, as in the water molecule, though there is only one octet 

 there are a number of positively charged atoms outside it, 

 the electron might attach itself to one of these atoms without 

 destroying the equilibrium of the cell. 



It is interesting to find that, as shown by observations on po- 

 sitive rays, radicles such as OH, CH 2 , CH 3 , which are highly 

 unsaturated molecules, readily acquire negative charges. 



The ability of an atom to receive a negative charge 

 depends on its positive core being able to hold in stable 

 equilibrium one more electron than is found in the outer 

 layer of the neutral atom : thus the existence of the negative 

 hydrogen atom shows that a single positive charge can hold 

 two electrons in stable equilibrium ; the negative carbon 

 atom shows that a positive charge 4 can hold 5 electrons in 

 stable equilibrium; the negative oxygen atom that 7 electrons 

 can be held by a charge 6 ; and the negative chlorine atom 

 that 8 can be held by a charge 7. The absence of a nega- 

 tively electrified nitrogen atom is remarkable, since the atoms 

 of the elements on either side of it readily acquire a negative 

 charge. The reason may be that, though the nitrogen atom 

 could hold a negative charge if it could get it, it is not able 

 to snatch one from the molecules of the gas through which 

 it is passing. 



When the number of electrons in a molecule is less than 

 eight, as it would be in such compounds as NaH, BeEU, BH 3 , 

 the molecules might be expected, if they could be obtained in 

 the gaseous state, to behave something like an atom having 

 on its outer layer the same number of electrons as are present 

 in the molecule. These molecules might therefore be expected 

 to be able to acquire a positive charge. 



It is worthy of notice that, with the exception of hydrogen 

 and helium, no elements whose diatomic molecule contains 

 less than 8 electrons is gaseous at ordinary temperatures. We 



