Atomicity
The quantivalence or valency of the atoms; the number of combination
bonds, or bonds of affinity, possessed by the atoms of any substance.
Thus two atoms of hydrogen combine with one atom of oxygen, and three of
oxygen with one of sulphur, forming saturated compounds. Therefore,
taking hydrogen as of single atomicity or a monad, oxygen is of double
atomicity or a dyad, and sulphur is of six-fold atomicity, or a hexad.
The elements are thus classified into seven orders of atomicities, thus:
1, Monads or Univalent
elements, Hydrogen, etc.
2, Dyads or
Bivalent
" Oxygen, etc.
3, Triads or
Trivalent
" Nitrogen, etc.
4, Tetrads or
Quadrivalent "
Lead, etc.
5, Pentads or Quinquivalent
"
Phosphorous, etc.
6, Hexads or
Sexivalent
" Chromium, etc.
7, Heptads or
Septivalent
" Chromium, etc.
The same element often possesses several atomicities. Barium is
generally a dyad, sometimes a tetrad; nitrogen acts as a monad, dyad,
triad, tetrad and pentad. The familiar electrolysis of water, giving two
volumes of hydrogen to one of oxygen, is one of the illustrations of the
theory indicating that two atoms of hydrogen are combined with one of
oxygen.