Flemings: Electronics Indices
At this stage it may be well to indicate that any valid theory of electricity must involve an explanation of the facts of chemical combination and chemical valency as well. At present all ideas on the structure of atoms must necessarily be purely speculative.
So much advance has been made however in the development of a department of chemistry called stereo-chemistry that we need not despair of coming to know in time much about the architecture of atoms and molecules. The way is cleared, however, for some consistent explanations if we can assume that one or more free electrons can attach themselves to a neutral atom and so give it a negative charge of electricity.
We may suppose as a first assumption that in a neutral atom which is otherwise complete there exist localities at which one or more electrons can find a permanent attachment. The atom is then no longer neutral but negatively electrified. If the atom can as it were accommodate one electron it is a monovalent element, if two it is divalent and so on. If it cannot accommodate any at all it is an avalent or non-valent element. Consider the case of gaseous molecules. Chemical facts teach us. In these cases hydrogen and oxygen are so to speak combined with themselves. We can explain this by the supposition that most neutral atoms are unstable structures.
In contact with each other some lose one or more electrons and an equal number gain one or more electrons. Certain neutral atoms such as those of argon are monatomic and non-valent and these appear to be unable to enter into combination either with each other or with other atoms. Accordingly, in a mass of free hydrogen there are no free electrons and all the positively charged and negatively charged H atoms are in union. Hence the gas is a non-conductor of electricity. But we can make it a conductor by heating it to a high temperature.
The explanation of this is that a high temperature dissociates some of the molecules into atoms and these under the action of electric force move in opposite directions, thus creating an electric current. Thus air at ordinary temperatures is an almost perfect non-conductor, but at a white heat it conducts electricity freely. The monovalent elements like hydrogen are those neutral atomic structures which can lose one electron or take up one electron, becoming respectively positive atomic ions and negative atomic ions.
In the same way the divalent elements such as oxygen are those neutral atomic structures which can part with two electrons and take up two and so on for trivalent, quadrivalent, etc. The work required to remove the second electron probably is very much greater than that required to remove the first. Hence in polyvalent atoms the valencies have unequal energy values. Consider now a mass of intermingled oxygen and hydrogen consisting of neutral molecules. The state is a stable one as long as all the molecules are neutral. If, however, we dissociate a few of the hydrogen and oxygen molecules by an electric spark or by heat then there is a recombination.
A positive oxygen ion unites with two negative hydrogen ions and a negative oxygen ion with two positive hydrogen ions and the result is two neutral molecules of water. This combination takes place because the union of oxygen ions with hydrogen ions to form water evolves more heat and exhausts more potential energy than the combination of oxygen with oxygen and hydrogen with hydrogen ions in equivalent quantity.
The energy set free by the union of the O and H is sufficient to continue the dissociation of further gaseous molecules so the action is explosive and is propagated throughout the mass. There is however a broad distinction between the elements in this respect, viz. A metallic atom for instance is electropositive, but the atoms of non-metals are mostly electronegative.
Moreover metals in the mass are electrically good conductors, whereas non-metals in the mass are non-conductors or bad conductors. Thus we may consider that the metallic atoms lose very easily one or more electrons and also that there is a somewhat feeble attachment in their case between the neutral atom and the free electron.
Hence metals in the mass are conductors because there are plenty of free electrons present in them. On the other hand, in the case of non-metallic atoms the force required to detach one or more electrons from the atom is much greater and conversely the attachment of free electrons for the neutral atom is larger. Accordingly, in non-metals there are few free electrons and they are therefore non-conductors.
Moreover the presence of positive and negative atomic ions causes them to link together into more or less complex molecules and they exhibit polyvalency and act as the grouping elements in molecular complexes. This is a very characteristic quality of the elements, sulphur, silicon and carbon. Helmholtz long ago laid stress on the fact that certain physical and chemical effects could only be explained by assuming a varying attraction of electricity for matter. The same idea followed out leads to an hypothesis of chemical combination and dissociation of salts in solution.
Thus a molecule of sodic chloride is the electrical union of a monovalent sodium ion or sodium atom minus one electron with a chlorine ion which is a chlorine atom plus one electron.
It may be asked why in this case does not the extra electron pass over from the chlorine to the sodium ion and leave two neutral atoms. The answer is because the union between the electron and the chloride is probably far more intimate than that between the atomic groups. These latter may revolve round their common center of mass like a double star, but the electron which gives rise to the binding attraction may be more intimately attached to the atomic group into which it has penetrated. Any theory of electricity must in addition present some adequate account of such fundamental facts as voltaic action and magneto-electric induction.
Let us briefly consider the former. Suppose a strip of copper attached to one of zinc and the compound bar immersed in water to which a little hydrochloric acid has been added. All chemical knowledge seems to point to the necessity and indeed validity of the assumption that the work required to be done to remove an electron from a neutral atom varies with the atom. Conversely the attraction which exists between a free electron and an atom deprived of an electron also varies. Accordingly the attraction between atomic ions, that is, atoms one of which has gained and one of which has lost electrons, is different.
Upon this specific attraction of an atomic ion for electrons or their relative desire to form themselves into neutral molecules depends what used to be called chemical affinity. Hence a zinc atomic ion is more ready to take up electrons and again become neutral than a copper ion. Consider then the simple voltaic couple above described. In the electrolyte we have hydrogen ions which are H atoms minus an electron, and chlorine ions which are chlorine atoms plus an electron.
These are wandering about in a menstruum which consists of water molecules and hydrochloride acid molecules. Then in the metal bar we have zinc and copper divalent ions which are these atoms each minus two electrons, and also an equivalent number of free and mobile electrons. If we adopt Volta's original view of contact electricity, we must assume that at the surface of contact of the metals there is some action which drives electrons across the boundary from the zinc to the copper.
This may be due to the neutral copper atoms having a slightly greater attraction for electrons than the neutral zinc atom. The zinc is therefore slightly electrified positively and the copper negatively. Accordingly in the electrolyte the negative chlorine ions move to the zinc and combine with positive zinc ions, forming neutral zinc chloride, two chlorine ions going to one zinc ion. The hydrogen ions therefore diffuse to the copper side and each takes up a free electron from the copper, becoming neutral hydrogen atoms and there escape.
In proportion as the zinc atomic ions are removed from the zinc bar and the corresponding free electrons from the copper, so must there be a gradual diffusion of electrons from the zinc bar to the copper bar across the metallic junction.
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But this constitutes the voltaic current flowing in the circuit. It is a current of negative electricity flowing from zinc to copper and equivalent to a positive current from copper to zinc. The energy of this current arises from the differential attraction of zinc and copper ions for chlorine ions and is therefore the equivalent of the exhaustion of the chemical potential energy of the cell. Thus the electronic theory outlines for us in a simple manner the meaning of voltaic action.
Even if we do not admit the existence of a metallic junction volta contact force, the theory of the cell may be based on the view that the movement of the saline ions in the electrolyte is determined by the law that that motion takes place which results in the greatest exhaustion of potential energy. Hence the chlorine ions move to the zinc and not to the copper. In the same manner the electronic theory supplies a clue to the explanation of the production of an electric current when a conductor is moved across a magnetic field.
Every electron in motion creates a magnetic force. Hence a uniform magnetic field may be considered as if due to a moving sheet of electrons. This, however, would involve at the moment of starting a backward push on surrounding electrons, just as when a boat is set in motion by oars the boat is pushed forward and the water is pushed back.
Hence there is an induced current at the moment when the field begins in the conductor. Similarly the reaction at stopping the procession would drag the surrounding electrons with it. Accordingly the induced currents when the field ceases is in the opposite direction to that when it begins. The electronic theory has in the hands of other theorists such as Professors P.
Drude and E. Riecke been shown to be capable of rendering an account of most thermomagnetic effects on metals, contact electricity, the so-called Thomson effects in thermoelectricity, and also the Hall effect in metals when placed in a magnetic field. Soc, , , Electrons can therefore be either positive or negative according to the direction of the strain and to every positive electron there is a corresponding negative one.
Atoms according to him are collocations of electrons in stable orbital motion like star clusters or systems. The discovery by Zeeman of the effect of a strong magnetic field in triplicating or multiplicating the lines in the spectrum of a flame placed in a magnetic field meets with an obvious explanation when we remember that the effect of a magnetic field on an electron in motion is to accelerate it always transversely to its own motion and the direction of the field. Hence it follows that a magnetic field properly situated will increase the velocity of an electron rotating in one direction and retard it if rotating in another.
But a linear vibration may be resolved into the sum of two oppositely directed circular motions and accordingly a magnetic force properly applied must act on a single spectral line, which results from the vibration of an electron in such manner as to create two other lines on either side, one representing a slightly quicker and the other a slightly slower vibration. The notion of an electron or point charge of electricity as the ultimate element in the structure of matter having been accepted, we are started on a further enquiry as to the nature of the electron itself.
In other words electrons must exist in pairs of such kind that their simultaneous presence at one point would result in the annihilation of both of them. On the view that material atoms are built up of electrons we have to seek for a structural form of atom which shall be stable and equal to the production of effects we find to exist. The first idea which occurs is that an atom may be a collection of electrons in static equilibrium.
But it can be shown that if the electrons simply attract and repel each other at all distances according to the law of the inverse square no such structure can exist. The next idea is that the equilibrium may be dynamic rather than static. That an atom may consist of electrons, as suggested by Larmor, in orbital motion round each other, in fact that each atom is a miniature solar system. Against this view, however, Mr. Jeans 'Mechanism of Radiation,' Proc.
If we are to assume an atom to consist wholly of positive and negative electrons or point charges of electricity, Mr. Jeans has indicated that we may obtain a stable structure by postulating that the electrons, no matter whether similar or dissimilar, all repel each other at very small distances. The difference between the total number of positive and negative electrons is the valency of the atom.
On this view an atom of hydrogen would consist of from to 1, positive and negative electrons arranged in concentric layers in a spherical form. The vibrations which emit light are not those of the atom as a whole but of the individual electrons which compose it. The reason for assuming that in all cases the outermost layer of electrons is negative is that if it were not so, if some atoms had their outer layers of negative and some of positive electrons, two atoms when they collided would become entangled and totally lose their individuality.
There would be no permanence. Hence our present atoms may be, so to speak, the survivors in a struggle for existence which has resulted in the survival only of all atoms which are of like sign in the outer layer of electrons. We see an instance of a similar action in the case of the like directed rotation of all the planets round the sun which is due to the operation of the law of conservation of angular momentum.
As a consequence of the equality of sign of the outer layer of electrons two atoms cannot approach infinitely near to each other. They mutually repel at very small distances. This suggestion makes it clear why we only know at present free negative electrons; it is because we can only detach a corpuscle or electron from the outer layer of an atom. It is clear, however, that the complete law of mutual action of electrons has yet to be determined. We have also to account for gravitation and this involves the postulate that all atomic groups of electrons without regard to sign must attract each other.
Hence we need some second Newton who shall formulate for us the true law of action of these electrons which form the 'foundation stones of the material universe. That at greater distances positive electrons repel positive and negative repel negative, but unlike electrons attract, with a force which varies inversely as the square of the distance. Superimposed on the above there must be a resultant effect such that all atoms attract each other at distances great compared with their size without regard to the relative number of positive and negative electrons which compose them, inversely as the square of the distance.
In this last condition we have the necessary postulate to account for universal gravitation in accordance with Newton's law.
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In other words, every atom attracts every other atom; but every electron does not attract every other electron. Universal gravitation may be an effect due to the collocation of electrons to form atoms and molecules, but not an attribute of electrons in themselves, though, if the gravitative effect is proportional to the product of the total number of electrons in each mass, the Newtonian law will be fulfilled. It has been also suggested that a sufficient source for the necessary resultant mass attraction may be found in a slight superiority of the attractive force between two opposite electrons over the repulsion between two similar electrons.
In the above sketch of the electronic theory we have made no attempt to present a detailed account of discoveries in their historical order or connect them especially with their authors. The only object has been to show the evolution of the idea that electricity is atomic in structure, and thus these atoms of electricity called electrons attach themselves to material atoms and are separable from them. These detachable particles constitute as far as we yet know negative electricity. We have therefore to think of an atom as a sort of planet accompanied by smaller satellites which are the electrons.
Moreover the electrons are capable of an independent existence, in which case they are particles of so-called negative electricity. The atom having its proper quota of electrons is electrically neutral, but with electrons subtracted it is a positive atomic ion, and with electrons added to it it is a negative atomic ion. There is good ground for the view that when a gas is made incandescent, either by an electric discharge or in any other way, the vibrating bodies which give rise to the light waves are these electrons in association with the atom.
Lorentz, Helmholtz, Thomson and others have shown that such a conception of atomic structure enables us to explain many electro-optic phenomena which are inexplicable on any other theory. But the complications introduced by the presence of matter in the electric and magnetic fields presented immense difficulties which Maxwell's theory was not able to overcome. The electronic theory of electricity, which is an expansion of an idea originally due to Weber, does not invalidate the ideas which lie at the base of Maxwell's theory, but it supplements them by a new conception, viz.
We are then led to ask whether the atom is not merely a collocation of electrons. If so, all mechanical and material effects must be translated into the language of electricity. We ought not to seek to create mechanical explanations of electrical phenomena, but rather electrical ones of mechanical effects. All the facts of electricity and magnetism are capable of being restated in terms of the electron idea.
All chemical changes are due to the electric forces brought into existence between atoms which have gained or lost electrons. If moving electrons constitute an electric current, then electrons in rotation are the cause of magnetic effects. In optics it is capable of giving a consistent explanation of dispersion, absorption and anomalous dispersion and the relation of the index of refraction to the dielectric constant. A scientific hypothesis, with this wide embrace, which opens many closed doors and enables us to trace out the hidden connection between such various departments of physical phenomena, is one which must continue to attract investigators.
Physical enquirers are at present, however, groping for guiding facts in this difficult field of investigation, but we have confidence that mathematical and experimental research will in due time bring the reward of greater light. MAY By Dr. The Electronic Theory of Electricity. Thomson, F. Hidden categories: Subpages Pages with contributor. Namespaces Page Discussion. Views Read Edit View history. Citing Literature.
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