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|Topic: Dr. Abram's Electron Theory
William F. Hudgings
Section: Part V, The Electron Theory
Table of Contents to this Topic
| THE ELECTRON THEORY
When mention is made of "The Electron theory" some people imagine the phrase implies that the very existence of electrons is theoretical; that nobody really knows for a certainty whether such elemental particles of electricity constitute the structure of material atoms, but that the proposition is a scientific hypothesis. The following pages should dissipate that popular misconception. The theory does not concern the existence of electrons, for that has been experimentally established beyond question, but rather their arrangement and activity within the atom in an endeavor to account for hitherto unexplained phenomena. It is the purpose of this essay to depict in an orderly way the progress which modern scientists have made in their exploration of the intricacies of atomic structures by naming the discoveries that have been made and describing the experiments and apparatus employed. A line of demarcation will accordingly be drawn between fact and theory at every point.
Modern knowledge of the constitution of matter properly dates from the discovery of X-rays by Roentgen in 1895. Like many other important discoveries this one was an accident. While experimenting in a darkened room with an electric current and a Crookes tube, with no definite object in mind (so the story goes), Prof. Roentgen was amazed to discover the outline of his hand recorded upon a photographic plate which had been lying beneath a book on the working table. The impinging of the current upon the sides of the tube had generated certain peculiar light rays, invisible to the eye, but of strange, penetrating power before which the human hand and the book had appeared as porous. He called them X (that is, Unknown) rays. Roentgen's discovery stimulated scientists everywhere to undertake experiments along similar lines, and these investigations led almost immediately to the discovery by Becquerel of radioactive emanations from the mineral uranium. Both discoveries owe their inception to the development of photography, because each of them was revealed by their radio-chemical actions on photographic plates.
When in 1896 Prof. Becquerel found uranium possessed of this peculiar power to emit radiant energy continuously, Pierre and Mme. Curie and others began a series of investigations to account for the strange phenomenon. It did not at first occur to them that this emanation of energy, which seemed to controvert the law of the conservation of energy, really originated within the structure of the atom itself. They attempted to explain it on the theory that uranium is so constructed as to be able to store up within its molecules a quantity of energy which it receives from some outside source like the sun and that it in turn radiates this energy exactly as the earth radiates solar heat. Experiments were then made to ascertain if the radiation from uranium would be less at midnight than at high noon, due to the interposition of the earth's thickness between the radioactive substance and its supposed source of energy. No difference was detected.
The negative result of the last mentioned experiment led inevitably to the conclusion that these energy emanations must originate within the structure of the substance and are independent of any outside source. But the idea that radioactivity is a purely atomic phenomenon was a revolutionary one for chemists and physicists who had long regarded the atom as having no mechanical structure whatsoever. To them it was the ultimate division of the known elements and incapable of further structural analysis. The discovery of radioactivity, therefore, marked the beginning of a new era in the progress of physical science.
Other substances were then examined to ascertain if radioactivity is a property common to all matter or if uranium is unique in this respect. Thus it was that the Curies in 1897, while experimenting with mineral pitchblende, discovered therein an element which when isolated was found to give out radiant energy 4,000,000 times more intense, gram for gram, than that which emanates from uranium. This element they appropriately named radium. Other substances possessing radioactivity in varying degrees were shortly thereafter discovered, such as polonium, actinium, and thorium, but none that displays it so abundantly as does radium. Curies' discovery, therefore, opened wide the door to the investigation of radioactive phenomena and of the constitution of matter in general. Evidence now points to the fact that all matter possesses the quality of radioactivity to some extent, although only certain elements of high atomic weight display it sufficiently to produce effects on photographic plates.
No particular progress could be made in the field of physics so long as the atom was regarded as an indivisible elementary particle, incapable of further analysis. Chemists were, of course, familiar with the innumerable combinations of the various elementary atoms which constitute the endless variety of substances that go to make up a world or a universe. But why there are eighty or ninety different kinds of atoms, and just what constitutes the difference between them, were questions which were regarded as unanswerable. Scientists had contented themselves with quantitative rather than qualitative research into the basis of things. They were devoted to the problem of how much could be accomplished with the material in hand rather than with the intricacies of the mechanism itself.
But with the discovery of the strange property of radioactivity it became manifest that something more than the mere chemical combination of atoms into molecules was involved. Chemists knew these chemical combinations from A to Z, but that knowledge was incompetent to explain the source of these remarkable emanations of radiant energy. They realized that these chemical combinations have nothing to do with the problem; that the phenomenon is wholly elementary and must emanate from within the atoms. This was demonstrated when it was found that radioactivity continues unabated even after the molecules or atomic combinations of the radioactive substance are disintegrated. This being so there could be no other conclusion than that the atom is a complex structure possessing internal activity and energy instead of being a lifeless elementary particle of matter incapable of divisibility or dissection.
If the atom is thus an active, composite structure, how is it made and from what kind of matter is it formed? May it not be that all types of atoms are made from the same original stuff, but simply put together according to different patterns? May not the hitherto "unsolvable" problem of the basic difference between elements really be solved after all? These and many similar questions now filled the minds of earnest investigators and daily clamored for solution. Numerous experiments were undertaken and much scientific data was amassed during the years immediately following the discovery of radium. Thus by 1903 Prof. Ernest Rutherford, in collaboration with Prof. F. Soddy and others, was able to propose a concrete theory of atomic structure which fully accounted for the phenomena exhibited by radioactive substances and plausibly explained the fundamental differences, between the various known elements. So carefully was their theory constructed that twenty years of most critical research since that time has not shaken but has strengthened their hypothesis by adding thereto certain interesting details which make this now accepted Electron Theory of Matter unique in its completeness. The following pages will set forth in simple language the details of the theory and the discovered facts upon which it rests, giving also a brief explanation of the apparatus and methods of experimentation.
WHAT ARE ELECTRONS ?
The modern confirmed hypothesis of the constitution of matter declared that all atoms consist entirely of elemental charges of electricity. These charges are called electrons, a name suggested by Dr. G. Johnstone Stoney as "the natural unit of electricity" several years before anybody knew anything about the structural nature of atoms. Both positive and negative electrons reside together within the atom, and are complementary to one another. Recently the name proton has been suggested for the positive electron, so as to distinguish it from the negative electron. We will so refer to it in this essay, and will apply the word electron only to the negative particle.
Electricity is not a fluid like ethereal nothing as many people indefinitely imagine. It is tangible matter in its basic form, and is granular in nature. But these grains (electrons and protons) are so infinitesimal that untold billions of them would be required to make a mass large enough to be observed through a powerful microscope. Yet they have been measured and analyzed, not directly but indirectly, by means of the effects which they produce. Their diameter is one hundred-thousandths that of an atom of hydrogen (the smallest atom known); and the hydrogen atom's diameter is known to be one fiftieth of a millionth of a centimeter. A centimeter is less than two fifths of a British inch. In our school days we were correctly told that if an orange were magnified until it became as large as the moon even then its atoms would be no larger than ordinary marbles. But in that event the electrons which compose the atoms would still be invisible to the naked eye.
The layman is not to be blamed for skeptically asking "How do scientists know so much about electrons and atoms inasmuch as both are invisible even with the most powerful microscope?" And "Isn't it mostly guesswork anyway, with one guess about as good as another concerning such infinitesimal things?" These queries are legitimate and require an answer. It is the purpose of this treatise to give to the reader, in nontechnical terms a history of the research work in this field up to the present moment, that he may reasonably determine what is theory and what is actual discovery.
Literally speaking, all conclusions which are arrived at by deduction are theoretical; but when theory has been corroborated by independent modes of calculation it is then elevated from the realm of fancy to the plane of reasonable fact. It is true that no human being has seen or can see an atom of matter, much less to look within it and observe its complex electronic mechanism. Nevertheless these minute particles, when emitted by highly radioactive substances like radium, can be made to produce visible effects in a gaseous medium through which they may pass, cause phosphorescent screens to become luminous, and make impressions upon sensitized photographic plates. These and many other producable effects are capable of analysis and logically lead to certain definite conclusions. Any effect must have a competent cause, and from an aggregation of effects that have been produced by the same factor much definite knowledge may often be gained concerning that factor.
We have already seen how that early experiments demonstrated the fact that radioactive substance emit the same amount of energy at midnight as at high noon thereby proving that the action of the sun's rays has nothing to do with radioactive phenomena. The next experiment undertaken was to ascertain if temperature of the substance would increase or decrease its radioactivity. This experiment likewise gave negative results. Radium was also found to be equally active whether in the solid or in the dissolved state. These results show that the emission of these particles is not only independent of outside force but that it is likewise independent of the molecular constitution of the substance. Here, then, we have laboratory proof, not theory, that the radiation emanates from within the atom. Therefore the atom must have activity within it, revolving or vibrating parts; and the energy of these moving parts must be enormous since they impart such high velocities to the emitted particles. Thus the first step was taken on the scientific exploring expedition into the unknown depths and structural complexities of the atom.