Atomic theory

“ In the meanwhile, the primitive atomic theory, which has served as the scaffolding for the edifice of modern physics and chemistry, has been quietly dismissed. I cannot discover that any contemporary physicist or chemist believes in the real indivisibility of atoms, or in an interatomic matterless vacuum. 'Atoms' appear to be used as mere names for physico-chemical units which have not yet been subdivided, and 'molecules' for physico-chemical units which are aggregates of the former. ”

“ The Atomic theory corrected or modified this opinion, and this correction followed as a consequence of the Atomic doctrine in regard to the constitution of material things. If the atoms, the ultimate constituents of all things, are identical in point of quality, and differ only in size, shape, position, and arrangement, it follows that there can be nothing in real nature corresponding to what we call heat or cold, or sweet or bitter, or colour. These are merely sensations in us; not only are they mere sensations in us, there are, moreover, no qualities in things by which they are induced. ”

“ He first definitely formulated the atomic theory as a scientific hypothesis. The whole physical and chemical science of that century was now based upon the atom, and it is quite a mistake to suppose that recent discoveries have discredited "atomism." An atom is the smallest particle of a chemical element. No one has ever seen an atom. Even the wonderful new microscope which has just been invented cannot possibly show us particles of matter which are a million times smaller than the breadth of a hair; for that is the size of atoms. ”

“ It is, however, simply a theory, and from the very nature of the hypothesis is incapable of proof. No one has ever seen an atom of hydrogen or oxygen, or an atom of any solid, liquid, or gaseous matter. The Atomic Theory suggests, therefore, that there is a limit to the divisibility of matter. All chemical experiments lend support to the theory, and by it we are able to give an intelligible and easy method of expression to what would otherwise be difficult phenomena to explain. ”

“ An adequate theory of material phenomena is necessarily ultimately atomic. The older mathematical type of atomic theory which regards the atoms of matter as acting on each other from a distance by means of forces whose laws and relations are gradually evolved by observation and experiment, is in the present method expanded end elucidated by the introduction of a medium through whose intervention these actions between the material atoms take place. ”

“ As the forces which one atom exerts on another depend on the rearrangement of the electrons in the atom, the forces which a neutral atom exerts on other atoms—what we may call the social quantities of the atom—will depend mainly on the outer belt of electrons. Now these forces are the origin of chemical affinity, and of such physical phenomena as surface tension, cohesion, intrinsic pressure, viscosity, ionising power, in fact of by far the most important properties of the atom; and the most interesting part of the atom is the outside belt of electrons. ”

“ It is here that the chemist with his atomic theory of matter comes to our aid. He assures us that all matter consists in the last analysis of excessively minute particles, and that these particles are perpetually in motion. They unite with one another to form so-called molecules, but they are perpetually breaking away from such unions, even though they re-establish them again. Such activities of the atoms take place even in solids, but they are greatly enhanced when any substance passes from the solid into the liquid state. ”

“ By means of the electric spectrum we can prove in a very direct and striking way some of the fundamental truths of the Atomic Theory. For example, when we form the electric spectrum of a mixture of gases, such as the air, we get a limited number of sharply-divided streams, which show no tendency to merge into each other. This shows that the gas contains only a few kinds of particles, and that all the particles of one kind have exactly the same mass, for if there had been any variation in the masses the streams would have been fuzzy. This shows that all the atoms of an element are alike ”

“ We may, I think, get a useful lesson by considering for a moment from this point of view a theory of the atom which, though it is not in very close touch with physical phenomena, has yet the advantage of being so precisely defined that the properties of its atoms can be deduced by purely mathematical principles. The theory to which I allude is that known as the 'Vortex Atom Theory of Matter', which supposes that the Universe consists of an ideal substance known to mathematicians as a perfect fluid. ”

“ The leading historical stages in the evolution of the modern conception of the molecular structure of matter are treated in the following passage from James Clerk Maxwell’s article Atom in the 9th edition of the Ency. Brit.
“Atom [1] (ἄτομος) is a body which cannot be cut in two. The atomic theory is a theory of the constitution of bodies which asserts that they are made up of atoms. ”

“ Lastly, we know that there are regions in the atom, probably the most interesting of all, about which we know little or nothing, whose investigation will provide intensely interesting work for many generations of physicists, who will most assuredly have no reason to be 'mournful that no new wonder may betide'. No fact discovered about the atom can be trivial, nor fail to accelerate the progress of physical science, for the greater part of natural philosophy is the outcome of the structure and mechanism of the atom. ”

“ In recent years we have come to realize that matter is not the manifold material we were accustomed to think it when we accepted the hypothesis that there were some seventy odd different kinds of atoms, each one absolutely independent of any other and representing an ultimate term in science. The atomic theory from this standpoint has proved to be only a working hypothesis that was useful for a time, but that our physicists are now agreed must not be considered as something absolute. ”

“ In one form of a theory which has rendered great service to physical science—I mean Planck's theory of the 'quantum'—the changes from radiant to kinetic energy are supposed to occur not continuously, but by definite steps, as would inevitably be the case if the energy were atomic in structure. ”

“ Collapse of the Atomic Theory.—Dalton's theory of atoms was described in a previous chapter. It is hardly possible to exaggerate the importance attached by materialists, ever since Lucretius, to the conception of indivisible and indestructible atoms. It was regarded as integral to materialism, and never was the prestige of this theory higher than during the nineteenth century, which "will go down in scientific history as the era of the atomic theory of matter." ”

“ We see that changes in the atom large enough to change the chemical character of the atom, i.e. to split an atom of one element up into different kinds of atoms, involve enormous transformations of energy; in fact the explosion of the atom in a few pounds of material might be sufficient to shatter a continent. We are living in the midst, nay, are made up of quiescent volcanoes ”

“ The amount of energy required to break up an atom has a very important bearing on the problem of splitting up the atom, in other words the transmutation of the elements by physical means. We know that the atoms of the radio-active elements break up spontaneously, and give rise to atoms of another kind. Thus radium emanation splits up into helium and radium A, and radium A again splits up. ”

“ We have so far implicitly assumed that the great majority of scientific men now regard the atomic theory not only as a working hypothesis of great value but as affording a correct description of one stage of the sub-division of matter. ”

“ There is much that might indicate that, on the whole, it is impossible to obtain a consistent picture of atomic processes in space and time with the help of the motions of the nuclei and the electrons and the variations in the state of the ether, and with the application of such fundamental conceptions of physics as mass, electric charge and energy. ”

“ We have seen that the view, so strongly supported by recent experiments, that the atoms of the elements are aggregations of simpler systems, involves the admission that losses or gains of mass or weight must occur in the formation of the heavier atoms. But we know that the ratio of mass to weight is the same for all substances, from hydrogen, the lightest, up to uranium, the heaviest, and even, as Southern's experiments on uranium and my own on radium have shown, for radio-active substances. ”

“ With such penetrating agents as Röntgen and cathode rays at our disposal, other properties which the atom retains unaltered have been brought to light, such, for example, as the absorption of these rays when they pass through atoms; the absorption by a given atom is quite independent of any other atoms with which it may happen to be associated, and depends only on the quality of the atom itself. ”

“ It can be shown that any portion of this fluid which once possesses rotatory motion will never lose it, while if it does not at any instant possess it, it can never acquire it; the atoms on this theory possess at any rate some of the characteristics of real atoms, as they can neither be created nor destroyed. The atoms of one substance on this theory are differentiated from those of another, not merely by the quantity of the rotating liquid, but also by the speed with which it is rotating. ”

“ How many atoms are at least necessary in order that a process may be considered irreversible?, the answer is: so many atoms that one may form from them definite mean values which define the state in a macroscopic sense. One must reflect that to secure the validity of the principle of increase of entropy there must be added to the condition of elementary disorder still another, namely, that the number of the elements under consideration be sufficiently large to render possible the formation of definite mean values. ”

“ It seems clear, however, that we need have no fear that in investigating the problem of atomic energy we are releasing forces which we cannot control, because we can at present see no way to liberate the energy of atomic nuclei beyond that which Nature herself provides, to say nothing of a practical solution of the energy problem. ”

“ We can produce a system which is still simpler than the ordinary hydrogen atom, for we can extract the electron from the atom and get merely the positive charge left: these positively charged hydrogen atoms exist in large numbers in the positive rays. ”

“ Upon the whole, it would seem that the validity of the first proposition of the atomic theory is not sustained by the facts. Even if the assumed unchangeability of the supposed ultimate constituent particles of matter presented itself, upon its own showing, as more than a bare reproduction of an observed fact in the form of an hypothesis, and could be dignified with the name of a generalization or of a theory, it would still be obnoxious to the criticism that it is a generalization from facts crudely observed and imperfectly apprehended. ”

“ From the point of view of the nucleus theory, the atomic weight of an element, while in some cases approximately proportional to its atomic number, is in reality a complicated function of the actual structure of the nucleus. The question why the atomic mass should not necessarily be proportional to the atomic number has already been discussed. While the main properties of an atom are controlled by its nuclear charge, the property of gravitation and also that of radioactivity are to be ascribed mainly, if not entirely, to the nucleus. ”

“ When the missing atomic weight 0.0302 is multiplied by the square of the velocity of light according to Einstein’s theory, it is found to represent a tremendous amount of energy. Indeed, the energy released in forming a helium nucleus from two protons and two neutrons turns out to be seven million times that released when a carbon atom combines with an oxygen molecule to produce a molecule of carbon dioxide in the familiar process of combustion. ”

“ As we have proved that the atoms contain these electrons, the next step is to find out how many there are in any particular kind of atom. This was first done by the following method. When Röntgen rays fall on an electron, the rays are scattered just as light is scattered by the small particles of carbon in the smoke from a peat fire, or by the molecules of air in the upper regions of the atmosphere producing the blue of the sky ”

“ In the discussion of these questions, it must be kept in mind that, according to the view taken above, radiation in free space as well as isolated material particles are abstractions, their properties on the quantum theory being definable and observable only through their interaction with other systems. ”

“ The very nature of the quantum theory thus forces us to regard the space-time co-ordination and the claim of causality, the union of which characterises the classical theories, as complementary but exclusive features of the description, symbolising the idealisation of observation and definition respectively. ”

“ Do they not also indicate that any alteration in the specific gravity of the atom would give rise to a new series of compounds, thus apparently producing a new element? Surely there is nothing irrational in the idea that the influences of heat or electricity, or of other powers of which as yet we know nothing, may be sufficient to effect such changes in the atomic constituents of this earth.
The combination of elementary atoms takes place under the influence of an unknown force which we are compelled to express by a figurative term, affinity. ”