Atomic mass

“ The conception of atomic structure which will form the basis of all the following remarks is the so-called nuclear atom according to which an atom is assumed to consist of a nucleus surrounded by a number of electrons whose distances from one another and from the nucleus are very large compared to the dimensions of the particles themselves. The nucleus possesses almost the entire mass of the atom and has a positive charge of such a magnitude that the number of electrons in a neutral atom is equal to the number of the element in the periodic system, the so-called atomic number. ”

“ In all the foregoing calculations we have assumed that the mass of the nucleus is infinitely great compared to that of the electron. This is of course not the case, even though it holds to a very close approximation; for a hydrogen atom the ratio of the mass of the nucleus to that of the electron will be about and for a helium atom four times as great. ”

“ The real value of the new atomic hypothesis, however, did not lie in the two points which Democritus and his followers would have considered essential—namely, the indivisibility of the 'atoms' and the presence of an interatomic vacuum—but in the assumption that, to the extent to which our means of analysis take us, material bodies consist of definite minute masses, each of which, so far as physical and chemical processes of division go, may be regarded as a unit—having a practically permanent individuality. Just as a man is the unit of sociology, without reference to the actual fact of his divisibility, so such a minute mass is the unit of physico-chemical science—that smallest material particle which under any given circumstances acts as a whole. ”

“ If the volume be doubled, then the density of the body would be halved, and vice versâ, but through all the changes of volume and density that may arise from the addition of heat or diminution of heat, the total mass of a body always remains the same. Looked at from the atomic standpoint, taking hydrogen as unity, an atom of oxygen would always weigh sixteen times an atom of hydrogen, and this principle applies throughout the whole realm of the atomic world. ”

“ 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. ”

“ Since the atomic weights of the elements show that in their formation a measurable change of mass has taken place, the changes of energy involved in the formation of the elements must be enormous compared with those liberated in any chemical changes with which we are acquainted. ”

“ All nuclei (except hydrogen) weigh less than the sum of the weights of the particles in them.
For example, the atomic weight of a proton is 1.00812 and that of a neutron is 1.00893. (These are relative weights based on an internationally accepted scale.) It would seem then that a nucleus of helium containing two protons and two neutrons should have an atomic weight of 2 × 1.00812 plus 2 × 1.00893 or 4.0341. Actually the atomic weight of helium as measured by the mass spectrograph is only 4.0039. ”

“ It is entirely in accordance with electrical principles that some change in mass should occur when these primordial atoms coalesce; we know, for example, that when we push two similarly electrified bodies together against their mutual repulsion, the mass of the two increases by an amount proportional to the work done in pushing them together. ”

“ A diminution of mass means a liberation of energy proportional to it, so that the amount of energy liberated in the formation of these lighter elements will be proportional to the defect of this atomic weight from the nearest integer. ”

“ 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. ”

“ Since it is the positive charge carried by the nucleus of an atom which fixes the number of negative electrons needed to complete the atom, the nuclear charge is really responsible for the exterior appearance, or chemical properties, of the atom. ”

“ It is known that the sun consists chiefly of hydrogen and that it has a temperature of about 40,000,000 degrees Fahrenheit near its center. Several kinds of nuclear reactions produced in atom smashers have demonstrated that hydrogen nuclei, if energized by being heated to a very high temperature, can actually combine, or fuse, to form helium nuclei.
The accompanying loss of weight per particle indicated by Figure 4 must result in the appearance of sufficient energy to balance Einstein’s famous equation. ”

“ This final equation gave explicit instructions to the understanding; it told just how to completely destroy matter! It told how to release such terrific energy, I was afraid to try it. The equations of atomic energy I had tested and found good, I had succeeded in releasing the energy of atoms.
"But the energy of matter has been known for many years; simple arithmetic can calculate the energy in one gram of matter. One gram is the equivalent of about ten drops of water and that much matter contains 900,000,000,000,000,000,000 ergs of energy, all this in ten drops of water! ”

“ As soon as an atom is formed out of protyle it is a store of energy, potential (from its tendency to coalesce with other atoms by gravitation or chemically) and kinetic (from its internal motions) . To obtain this energy, the neighbouring protyle must be refrigerated by it, and thereby the subsequent formation of other atoms will be accelerated. But with atomic matter the various forms of energy which require matter to render them evident begin to act; and, amongst others, that form of energy which has for one of its factors what we now call atomic weight. ”

“ Its area is about 100 million times smaller than the area of the atom as a whole. If a piece of matter is bombarded by an energetic particle, chance alone will determine whether the particle is directed toward a nucleus. To be sure, if the particle misses the nucleus of one atom, it still has the opportunity of hitting the nuclei of other atoms which may lie in its path. It 52 does not have many such opportunities, however, because, being charged, it constantly interacts with the atomic electrons, which gradually absorb energy causing the particle to slow down. ”

“ We have seen that it is believed that the nuclei of all atoms are composed of protons and electrons and that the number of each of these units in any nucleus can be deduced from its mass and nuclear charge. ”

“ 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. ”

“ 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. ”

“ In a historic lecture delivered in Washington, D. C., in April 1914, Rutherford said, “It is possible that the nucleus of an atom may be altered by direct collision of the nucleus with very swift electrons or atoms of helium (i.e., beta or alpha particles) such as are ejected from radioactive matter.... Under favorable conditions, these particles must pass very close to the nucleus and may either lead to a disruption of the nucleus or to a combination with it.” ”

“ By our knowledge of radioactivity we can make our answer a little more learned, a little less abrupt, but none the less discouraging to the advocate of the development hypothesis. We can tell how the elements of high atomic weight, such as uranium and thorium, are constantly giving off particles and are thus by loss or decomposition being changed over into other elements, such as radium, niton, polonium and lead. ”

“ At this temperature, a further, subtle change takes place, and the electrons and the protons suddenly are gone, and in their place is an equal mass of energy. For energy in any form has mass, and mass in any form is a measure of the energy content. Thus to say "one gram" is an easier way of saying "nine hundred million million million ergs," but the two mean the same to Nature. Now an atom is something like a porcupine with his quills up; it is much bigger in looks than in fact, only an atom has much longer "quills." An atom has much more empty space than anything else. ”

“ For example, slow positive particles pick up electrons, become neutral, and lose their ability to cause nuclear transformations. Slow neutrons, on the other hand, can enter nearly all atomic nuclei and induce fission of certain of the heavier ones. It is, in fact, these properties of the neutron which have made possible the utilization of atomic energy.
With these tools, researchers were not long in accurately identifying the missing elements 43, 61, 85, and 87 and more—indeed, the list of new elements, isotopes, and particles now seems endless. ”

“ It appears, therefore, that these rapidly rotating systems of heavy atoms, such as characterize radio-active substances, not infrequently become unstable and project off a part of their mass. These particles which are first projected were found to be the alpha particles, and this process of projecting the alpha particles is the first stage of radio-activity. The mass which is left behind, namely, the uranium X, the thorium X, or the emanation, according as the original atom was uranium, thorium or radium, is itself unstable, and projects still other particles. ”

“ Helium nuclei are much less easily deflected from the straight line than electrons, showing that they have much greater mass. By exposing these particles to electric and magnetic forces and observing the effect upon their motion, it is possible to calculate their velocity and their mass. By one means or another, it is possible to find out just as much about them as we can find out about larger bodies.
An atom differs from the solar system by the fact that it is not gravitation that makes the electrons go round the nucleus, but electricity. ”

“ The study of the radio-active substances and of the discharge of electricity through gases has supplied very strong experimental evidence in support of the fundamental ideas of the existing atomic theory. It has also indicated that the atom itself is not the smallest unit of matter, but is a complicated structure made up of a number of smaller bodies. ”

“ 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. ”