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Perkins: Addition to the Double Bond, I 
651 
by the rapidity with which it increases when the atoms are pulled 
apart. If, in the equilibrium position, the binding electrons are 
far within the shell boundaries of both C and D, the union is a 
strong one. If the binding electrons are close to the boundary of 
either C or D, the union is weak, and easily broken. This may 
be easily verified by noting that if the shells in figs. 3 and 4 
are pulled apart the binding force increases only very little and 
then rapidly decreases. 
The single bond. — When two shell boundaries intersect, each of 
the shell electrons near the intersection is drawn, by the foreign 
nucleus, toward the line joining the two nuclei. That is, there 
is an effective concentration of electrons toward the portion com- 
mon to both shells. Any number of electrons from one to six 
may be thus drawn into the common portion and serve as bind- 
ing electrons between the two atoms. When electrons are thus 
concentrated, however, the magnetic tendency to form pairs be- 
comes strong, so that the union with two shared electrons is very 
stable as compared to the union with one shared electron. 
Therefore, the latter has not been recognized as a chemical 
union, and the former has been called a single bond. 
According to the above hypothesis as to the distribution of 
electrons, in the single bond the electrons are in contact (prob- 
ably in “figure-eight” formation) and in a plane perpendic- 
ular to the line joining the two atoms. 
The benzene bond. — According to the writer’s view of the 
structure of benzene and similar compounds, the bond composed 
of three binding electrons is stable under certain conditions. 
The principal condition is that three atoms should be held 
rigidly with the lines joining their nuclei at an angle (in the 
case of carbon, for example, 120°) ; that is, between those 
favoring the formation 
(109°), and the formation, 
The special cases in which this bond is 
very stable will be discussed in a later paper. Ordinarily it 
has an instability comparable with that of the one-electron 
bond and the five-electron bond. 
The double bond. — When the concentrating forces mentioned 
above bring four electrons into the common portion of two shells, 
it seems that magnetic forces are strong enough to form two 
