Man's physical universe

xanabras

596 MAN IS MASTERING HIS MATERIAL WORLD

power, their valence is said to be zero.

rewritten to show valence changes:

The above reaction may now be

Valence 2(+ 2 - 2)

2 Ha + O2 >- 2H2O

In this case hydrogen, H2, has changed in valence from zero to

2 X (+ 1). It has therefore increased in valence.

Inasmuch as hydrogen is oxidized in the above reaction, an increase

in valence must therefore be oxidation. By the same reasoning the

loss in valence of oxygen must be reduction.

We now have a new and more general definition of oxidation and

reduction. Oxidation is the increase in the positive valence, while reduction

is a decrease in positive valence.

Thus many reactions which involve

neither oxygen nor hydrogen are still oxidation-reduction reactions because

the valences of elements are changed in these reactions; in fact every

reaction in which there is a change of valence is an oxidation-reduction

reaction. The term oxidation-reduction reaction is used because in every

reaction which involves oxidation there is always a loss in positive

valence by one atom which exactly equals the gain in positive valence

of another. An example of an oxidation-reduction reaction which

involves no oxygen or hydrogen is given as follows: when a globule of

mercury is rolled over a sheet of paper covered with mercuric chloride,

HgCh, it leaves a fluorescent path when exposed to ultraviolet light

because the mercury forms mercurous chloride, HgCl, which, unlike

mercuric chloride, HgCb, is fluorescent.

Valence + 2-2 2(+ 1 - 1)

HgCl2 + Hg —3- 2 HgCl

mercuric chloride mercury mercurous chloride

In this case the mercuric mercury is changed to mercurous mercury;

when metals have two valences, the lower valence is indicated by the suffix

0W5 as in mercnrous or cuprous, and the higher valence is indicated

by the sufftx ic as in mercuric and cuprzc. This reaction represents a

decrease in positive valence and is therefore reduction. The free

mercury increases in positive valence and is therefore oxidized.

According to the electron theory, changes in valence are the result

of a loss or gain of electrons; thus oxidation and reduction fundamentally

involve a gain or loss of electrons by atoms or ions. Inasmuch as an

increase in positive valence is oxidation and inasmuch as this change

is accomplished by the loss of electrons, oxidation is the loss of electrons

or de-electronization, as the process is sometimes called. Reduction

must therefore be a gain of electrons, or electronization.

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