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Arrangement of Electrons in Atoms and Molecules.
J. Langmuir. The Arrangement of Elektrons in Atoms and Molecules. Physical Review 22, pp. 505, 587, 7895 (1919).
The theory is based on the ideas of Lewis’s “cubical” atoms1 and of Kossel’s saturated and unsaturated atomic shells2. Comparing the results of these works with Rydberg’s formula3, which expresses the atomic numbers of the noble gases in the form of the series: \(N = 2(1 + 2^2 + 2^2 + 3^2 + 3^2 + 4^2 + \cdots)\), the author comes to the conclusion that an entire series of physical and chemical properties of the elements and compounds can be explained if the following postulates are adopted.
1) The electrons in the atoms of the noble gases are arranged in pairs of planes, symmetrical with respect to the nucleus. The atoms have an axis of symmetry perpendicular to these planes.
2) The electrons are located inside a series of concentric spherical layers of equal thickness, the radii of which are related as \(1:2:3:4:\ldots\), and the surfaces as \(1^2:2^2:3^2:4^2:\ldots\).
3) Each spherical layer is divided into several cells of equal volume. The first layer (in essence, a sphere) contains two cells, separated from one another by an equatorial plane. The second layer is divided into 8 cells, the third into 18, etc.
4) Each of the two inner cells can contain only one electron; all the rest—two or one each.
5) The electrons act upon one another by electrostatic and electromagnetic forces which mutually balance one another.
6) If the limiting stable number of electrons in the outer layer is exceeded, electrostatic forces begin to predominate, and the excess electron is repelled into the next layer.
7) The properties of the atom are determined by the number of electrons in the outer layer.
8) The most stable and symmetrical arrangements of electrons are found in the noble gases, characterized by maximal internal forces with minimal internal fields.
9) The most stable system is the helium atom.
10) A very stable system is one consisting of one nucleus and eight electrons arranged around it (an “octet”).
11) Two “octets” may be mutually joined by one, two, three, or more pairs of electrons. In exactly the same way, a bond may also arise between an “octet” and a stable system constructed like a helium atom.
Not one of the electrons can participate in more than two “octets.” Electrons may pass from one “octet” into another.
The arrangement of the electrons in an “octet” may be of two kinds: either one each at the vertices of a cube (with the positive nucleus at the center), or two each (bound by electromagnetic forces) at the vertices of a regular tetrahedron.
In the atoms of all elements, except the inert gases, the outer electrons do not form complete “octets,” and therefore they enter into chemical combinations with one another, with electrons from one atom passing into another in order to form a complete “octet.”
Fig. 1.
Fig. 2.
Langmuir’s theory, unfortunately, as yet lacks mathematical treatment and does not explain why the electrons remain in their places in the state of rest (though the author refers to the work of J. J. Thomson, who investigated the equilibrium of atomic systems from the point of view of “tubes of force”); but the schemes proposed by Langmuir very clearly illustrate a whole series of chemical and physical processes: the formation of complex compounds, melting, boiling, and electrical conductivity.
As an example, let us present models of a) the water molecule and b) the nitrogen molecule.
a) In water, the black circle in Fig. 1 denotes the nucleus of the oxygen atom, the black crosses—the nuclei of the hydrogen atoms, and the white circles—the electrons. Electrostatic forces have displaced four electrons from the vertices of the cube, where they were located in the oxygen molecule.
b) A whole series of properties of nitrogen brings it close to the noble gases; therefore the model of the nitrogen molecule, according to the author’s theory, must have the form shown in Fig. 2, where the black circles denote the nuclei of the nitrogen atoms that have combined into a molecule, and the white circles—the electrons.
Vas. Shuleikin.