Man's physical universe



tween covalent compounds are relatively slow.

This difference in the

rates of reaction of electrovalent and covalent compounds is explained

nicely by assuming that in the case of electrovalent compounds the

molecules have already dissociated to form smaller particles and the

reaction is simply a joining together of the particles, whereas in the case

of covalent compounds the molecules must be broken up into smaller

units before reactions can take place and they must come together in a

special way.

2. The Phenomena of Electrolysis, Electrovalent compounds, such

as acids, bases, and salts, when dissolved in water or in a limited number

of other solvents, form solutions which will conduct the electric

current; solutions of nonelectrolytes will not conduct the electric current.

Electrovalent compounds are therefore called electrolytes because

their water solutions will conduct an electric current; and covalent

compounds are called nonelectrolytes because their water solutions will

not conduct an electric current. Chemical changes always accompany

the passage of an electric current through a solution, and the process is

called electrolysis.

In 1807 Sir Humphry Davy carried out some of the first of the recorded

experiments with electrolysis, in which he separated sodium and

potassium from their salts. His experiments led to the added information

that molten electrolytes, as well as their solutions, will


the electric current and be chemically altered. Later investigations

showed that hydrogen or a metal separates at the negative electrode

(or cathode), while a nonmetal, such as oxygen, chlorine, or iodine,

separates at the positive electrode (or anode).

Michael Faraday discovered a fundamental relation between the

quantity of electricity used and the amounts of substances liberated

at the electrodes. He found that the quantities of substances set free at

the electrodes are proportional to the amount of electricity passed and that

the same amount of current liberates chemically equivalent weights of

different substances. In other words, the amount of electricity necessary

to set free a gram-molecular weight of an element is proportional to its

valence. Faraday's laws were of great significance in that they showed

that the ordinary chemical equivalent weights are also electrical

equivalents. Thus chemistry and electricity were shown to be very

closely allied.

The Theory of Electrolytic


Dissociation Was Formulated by Svante

In 1887 Svante Arrhenius proposed what is known as the theory of

ionization, or electrolytic dissociation. According to his theory, mole-

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