738 The Philippine Journal of Science 1921 
no alteration in the number of electrons in the chlorine shell, 
which is the reason for not extending the new line across to 
the chlorine symbol. 
The formula: 0 : Cl : O : is in accord with the phys- 
ical and chemical properties of chlorine dioxide. This sub- 
stance has a melting point of —76° C., boils at 10° C., and has 
in the liquid condition a molecular volume of 45. Sulphur 
dioxide, : O : S O : which is almost isosteric with 
0 : Cl: O :, melts at —76°C., boils at—10°C., 
and has a molecular volume of 45. Chemically, ClO, is charac- 
terized by a certain metastability similar to that of a perfectly 
dry mixture of hydrogen and chlorine. 
THE HALF BOND 
The three-electron bond might be accorded a special symbol, 
but it is more convenient to consider it composed of a two-electron 
and a one-electron bond. Since the bond composed of two 
electrons has long been called the single bond, and that of four, 
the double bond, it is convenient to call the one-electron bond a 
half bond. The three-electron bond may be considered as @ 
single bond plus a half bond. 
As is shown in Table 1, the customary line for an unsatisfied 
bond or affinity unit may be used to represent “vacancy in the 
shell for one electron.” Two such lines from different atoms 
coalesce to form a normal union sign,—, again merely a straight 
line, joining two atomic symbols. Two affinity unit lines from 
the same atom may coalesce into the borrowing union sign, ™. 
Each of these union signs represents a pair of electrons uniting 
two atoms, and shows by the ends of the line where the two 
vacancies are filled. In the case of the half bond only one vacancy 
is filled, one electron only being shared. It is convenient to 
represent this by a line considerably shorter than the normal 
union line, and placed adjacent to the atom in whose shell a 
vacancy is filled. 
Although it is more convenient to consider the three-electron 
bond as made up of a single and a half bond, the half bond by 
itself is relatively unimportant. The half bond may explain cer- 
