METATHESIS 105combines, the reaction may be shown by an intersecting vertical
equation.
HC 2 H 3 O 2 ^ H+ + C 2 H 3 O 2 "
NH4OH ^ OH" + NH4+
1
H 2 O
Types of Reactions. A student who tries simply to remember
each chemical reaction which comes to his attention very soon
becomes bewildered, then discouraged so far as chemistry is con-
cerned, and finally he may acquire a dislike for the subject.
The remedy for this condition is to compare each new reaction
with those previously considered and to group together all those
which show such similarities as to warrant their being classified
as of the same type.
In the following pages several types of ionic reactions are dis-
cussed and illustrated with specific examples.
The most important distinction among the types is whether or
not a change of valence is involved. Valence, as we shall use the
term, is the algebraic number of unit electric charges on an ion
or radical.
TYPES OF IONIC REACTIONS
Metathesis — interchange of radicals — no change of valence.
(a) Precipitation.
(b) Neutralization.
(c) Displacement of a weak acid from its salt.
(d) Displacement of a weak base from its salt.
(e) Hydrolysis.
Formation of Complex ions — no change of valence.
Oxidation and Reduction — valence changes.
METATHESIS
Metathesis, or double decomposition, is one of the main types of
chemical reaction, and it takes place between two compounds, con-
sisting merely in an interchange of radicals, the positive radical of
the first compound pairing off with the negative radical of the
second, and the negative radical of the first pairing off with the
positive of the second. Such a reaction involves no change in
the valence of any radical concerned.