The power of combining with another element or
radical, i.e., the E number of atoms of other
elements with which the atoms of any one element
can combine directly. Hydrogen, for example, is
univalent and therefore can only become attached
to one atom of another element, e.g., it combines
with chlorine, another univalent element, atom for
atom, forming H-Cl (hydrochloric acid). Bivalent
elements, e.g., oxygen, can combine with two, such
as with two hydrogens, forming H 2 O.
Valencies up to eight are possible.