18 
The Philippine Journal of Science 
1921 
It would not be expected, however, that — N — could borrow 
from a strongly negative atom as — 0 — , forming such a com- 
pound as N 3o 0 ex N. 
In a few compounds the heavier atoms of this group show elec- 
tropositive tendencies. The salts of Bi 111 are good examples 
of how the weak forces toward completion of a shell may be 
entirely overcome by some stronger shell, and electrons lost, 
rather than gained, by the weakly negative atom. It has often 
been considered that in the formation of pentahalides the atoms 
of this group show a positive valence of 5. A comparison with 
vanadium, which of all the positive atoms has the greatest simi- 
larity to the trivalent negative atoms, is of interest. The most 
evident difference is that the halides and oxyhalides of this 
group indicate valences of 3 and 5, but never 4. Vanadium, as 
would be expected from the consideration of electrostatic forces, 
shows also a valence of 4. 
It is evident then, that the trihalides of this group have a 
stability which does not permit of the addition of one more halo- 
gen atom. When two are added they probably form a compound 
strictly analogous in structure to NH 4 C1 in most, if not all, 
cases . 17 Thus, PCl r , is tetrachlorophosphonium chloride: 
Cl Cl 
\ / 
p + - cr . 
X \ 
Cl Cl 
THE OXYGEN GROUP 
— 0 — — S— , — Se— — Te— , Ra F. 
Vacancies in shell = 2. 
In most compounds containing borrowing unions it is found 
that either — 0 — , or — S — is the borrowing atom. This is 
not surprising, as of all the atoms capable of acting in this way 
these two are the most electronegative. It is the borrowing 
union which explains the fact that the number of oxygen atoms 
which can attach themselves to a negative atom depends more 
on the size of that atom than on its valence. Thus we have 
Cior, S0 4 , POr- , Si0 4 , but NO3 - , and CO 3 . 
The sulphonium and oxonium salts, so familiar to organic 
chemists, are assigned formulas analogous to those of ammo- 
nium salts. 
17 cf. Langmuir, ibid, p. 919. 
