Similarly with
phosphates, arsenates, etc. In all these compounds it is impossible to
lay one's finger on any distinction as regards chemical behavior between
the compounds called atomic and those usually called molecular.
Two points remain to be mentioned: The first is the relationship between
alteration of adicity and two series (ous and ic) of compounds. Tin is
usually said to be dyad in stannous compounds and a tetrad in stannic
compounds, but in a compound like SnCl_{2}AmCl, is not tin really a
tetrad?
{Cl
{Cl
Sn {Cl
{NH_{4}
and yet it is a stannous compound, and gives a black precipitate with
H_{2}S; so that valency does not necessarily go with the series. The
second point is that an objection may be urged, as, for example, in
ammonium chloride (the lecturer stated above that here N was a pentad,
the addition of the chlorine having caused the N to assume the pentadic
character), it may be said, why should you not suppose that it is the
chlorine "which has altered its valency, and that the compound should be
written:
{H
{H
N { \
{H--Cl
{H/
There is something to be said for this view, but on the whole the
balance of the evidence is in favor of nitrogen being a pentad.
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