The Electronic Theory of Matter.
§ 81. Sir J. J. Thomson has elaborated this theory of the nature and constitution of matter; he has shown what systems of electrons would be stable, and has attempted to find therein the significance of Mendeléeff’s generalisation and the explanation of valency. There can be no doubt that there is a considerable element of truth in the electronic theory of matter; the one characteristic property of matter, i.e., inertia, can be accounted for electrically. The fundamental difficulty is that the electrons are units of negative electricity, whereas matter is electrically neutral. Several theories have been put forward to surmount this difficulty. Certainly the electron is a constituent of matter; but is it the sole constituent? Recent research indicates that, as already pointed out, all atoms consist of two distinct portions, a massive central nucleus, whose net charge is positive, surrounded by a number of electrons, just sufficient to neutralize this charge. The point of greatest interest is that the indicated number of free electrons is exactly the number which expresses the position of the element in the Periodic Table, reckoning helium as 2, lithium as 3, and so on; and it would seem that the chemical properties of the elements are determined entirely by these electrons, and are, therefore, not, strictly speaking, periodic functions of their atomic weights, as was formerly thought ([§ 78]), but of their atomic numbers. The exact nature of the nuclei of the various atoms has yet to be determined: in the case of the atoms heavier than helium they would appear to be made up of the nuclei of hydrogen and (or) helium atoms together with—in many cases—electrons insufficient in number to neutralize the positive charges associated with these.