In addition to
the model of the atom,
Niels Bohr also proposed a model of the
chemical bond.
He propose this model first in the article "Systems containing several nuclei" - the third and last of the classic series of articles by Bohr, published in November 1913 in ''
Philosophical Magazine''.
According to his model for a
diatomic molecule, the electrons of the atoms of the molecule form a rotating ring whose plane is perpendicular to the axis of the molecule and equidistant from the atomic nuclei. The
dynamic equilibrium of the molecular system is achieved through the balance of forces between the forces of attraction of nuclei to the plane of the ring of electrons and the forces of mutual repulsion of the nuclei. The Bohr model of the chemical bond took into account the
Coulomb repulsion - the electrons in the ring are at the maximum distance from each other.
Thus, according to this model, the
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Eart ...
molecule is a regular
tetrahedron
In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all the o ...
, in which center the carbon nucleus locates, and in the corners - the nucleus of hydrogen. The chemical bond between them forms four two-electron rings, rotating around the lines connecting the center with the corners.
The Bohr model of the chemical bond could not explain the properties of the molecules. Attempts to improve it have been undertaken many times, but have not led to success.
A working theory of chemical bonding was formulated only by quantum mechanics on the basis of the
principle of uncertainty
In quantum mechanics, the uncertainty principle (also known as Heisenberg's uncertainty principle) is any of a variety of mathematical inequalities asserting a fundamental limit to the accuracy with which the values for certain pairs of physic ...
and the
Pauli exclusion principle
In quantum mechanics, the Pauli exclusion principle states that two or more identical particles with half-integer spins (i.e. fermions) cannot occupy the same quantum state within a quantum system simultaneously. This principle was formulated ...
. In contrast to the Bohr model of chemical bonding, it turned out that the electron cloud mainly concentrates on the line between the nuclei, providing a Coulomb attraction between them. For many-electron atoms, the
valence bond theory
In chemistry, valence bond (VB) theory is one of the two basic theories, along with molecular orbital (MO) theory, that were developed to use the methods of quantum mechanics to explain chemical bonding. It focuses on how the atomic orbitals of ...
, laid down in 1927 by
Walter Heitler
Walter Heinrich Heitler (; 2 January 1904 – 15 November 1981) was a German physicist who made contributions to quantum electrodynamics and quantum field theory. He brought chemistry under quantum mechanics through his theory of valence bond ...
and
Fritz London, was a successful approximation.
References
Bibliography
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Chemical bonding
Quantum chemistry
Chemistry theories
Electron
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