PAPERS PRESENTED AT GENERAL SESSIONS , 49 



to any theory. It may be noted at once, however, that 

 if two electrons are to be placed between atoms for each 

 valence bond, it will in general lead to an even nnmber of 

 electrons in any molecule. Remarkably enough, all but a 

 very few of the hundreds of thousands of chemical com- 

 pounds do contain an even number of electrons. It may 

 be noticed that if we take the old valence theory of or- 

 ganic chemistry where carbon has four valence bonds 

 and hydrogen one, and assume that these valence bonds 

 link, not with each other, but from atom to atom, then the 

 electron in the Lewis theory of valence simply replaces 

 the valence bond in the old system. The application of 

 this theory of valence to organic chemistry in general, 

 then, becomes very simple. 



Since carbon combines with four fluorine atoms, we 

 might expect nitrogen to combine with five and oxygen 

 with six. But no such compounds occur. The reason ap- 

 IDears to be fairly obvious. The forces of repulsion be- 

 tween' the nitrogen and fluorine nuclei are so great that 

 the atoms refuse to remain in combination with each 

 other. When we come to the neon atom, we find a pe- 

 culiar state of affairs; neon does not combine with any 

 other atom. We might explain its refusal to combine 

 with nitrogen or oxygen as due to the repulsion of the 

 positive nuclei, but there appears to be no reason why it 

 should not take an electron away from a weak atom like 

 lithium. The conclusion which we are forced to is this : 

 Neon has eight electrons in its outer or valence shell. 

 There must be something about the geometry of the ar- 

 rangement of eight electrons about an atom which makes 

 it peculiarly satisfactory to the forces between the elec- 

 trons. Eight electrons may be comfortably arranged in 

 the outer surface of the atom but no more electrons may 

 be introduced into this arrangement. Sodium, with an 

 atomic number of eleven, resembles lithium in its prop- 

 erties and can acquire only one positive charge. That 

 is to say, it has only one valence electron. We must con- 

 clude then that in the sodium atom the eight electrons 

 are in a condition similar to the two electrons in the 

 lithium atom. AVe then represent tlie sodium atom as 



