Electrolysis : Electrons

The unvarying amount of the electric charge on univalent ions, and the simple multiple relation between the charges on multivalent ions, suggest at once that electricity, like matter, is divided up into atoms. It might be supposed that there were two kinds of unit charges, one positive and the other negative. A cation would then be an atom or radical plus one positive unit; and an anion would be an atom or radical plus one negative unit. This hypothesis of the atomic structure of electricity originated with Faraday, as we have seen, and was revived by Maxwell in 1874. Both expressed scepticism as to the atomic nature of electricity. In 1874, in a paper read to the British Association (not published until 1881) G. Johnstone Stoney calculated the charge associated with the hydrogen atom. Since the charge on 1.008 gm. of hydrogen is 96,500 coulombs, and since this amount of hydrogen contains 6.06 x 10²³ atoms, the unit charge is

96,500/6.06 x 10²³ = 1.592 x 10^-19 coulomb,

or (since 1 coulomb = 3 x 10⁹ electrostatic units), it is 4.776 x 10^-10 E.S.U. Stoney called this atomic charge the electron.

Helmholtz, in 1881, in discussing Faraday's laws of electrolysis, pointed out that "if we accept the hypothesis that elementary substances are composed of atoms, we cannot avoid concluding that electricity, positive as well as negative, is divided into definite elementary portions, which behave like atoms of electricity."

J. J. Thomson, in 1895, showed that the negative electron exists in the free state in the cathode rays, and it moves free by conduction in metals. The positive electron (positron), with the same mass but opposite charge to the negative electron (negation; usually simply "electron"), has only a very transient existence, and the positive charge of smallest mass capable of prolonged independent existence is the proton, which is the nucleus of the hydrogen atom.

One proton and one electron at some distance from it constitute the neutral hydrogen atom. The positive hydrogen ion (or hydrion) existing in solution is not the proton, but is a solvated proton, i.e. one associated with one or more molecules of solvent. The positive nuclei of other atoms contain both protons and neutrons, with external electrons to produce neutrality of charge, and according as the number of external electrons is less than or greater than in the neutral atom, a positive ion (cation) or negative ion (anion) is produced. A negative ion is an atom or radical plus one or more electrons; a positive ion an atom or radical minus one or more electrons. The charge of an ion may be represented by dots or dashes placed over the symbol; one dot denotes unit positive charge, one dash unit negative charge. Cl^-, H⁺, Cu⁺⁺, SO₄^-- may, therefore, be written as Cl', H˙, Cu˙˙, SO₄''. Another system of representing ions is Sn⁴⁺, FeC6N6^4-, etc. All these methods will be used in what follows.

The electron at rest has a mass of 1/1845 that of a hydrogen atom, i.e.,

1.66 x 10^-24 / 1845 = 8.9 x 10^-28 gm.

Protein crystallography
Chemistry guide
Electrolysis
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