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1.4 Types of binding ... The most important types of force are as follows: (a) Electrostatic forces. In an ionic crystal the attraction is mainly due… - Rudolf Peierls
" "1.4 Types of binding
... The most important types of force are as follows:
(a) Electrostatic forces. In an ionic crystal the attraction is mainly due to the Coulomb interaction between point charges. This is particularly amenable to calculation, and a great deal of work has been done on it. The force is a 'two-body' force, i.e. the interaction between two given ions is independent of the positions of any other ions that may be present. ...
(b) Van der Waals forces. This name describes the effect that a neutral and isotropic atom can acquire a polarization under the influence of an electric field, and even two neutral isotropic atoms will induce small dipole moments in each other, due to the fluctuating moments which they possess because of the existence of virtual excited states. ...
(c) Homopolar binding. These are forces like those effective in homopolar molecules, and we know they are due to the exchange of electrons between the atoms. In molecular crystals (H<sub>2</sub>, Cl<sub>2</sub>, etc.) these bonds can easily be localized and we can start from a description of the molecular by the methods of quantum chemistry and then add the relatively weak forces between different molecules. In other cases, however, such as diamond or graphite, each atom shares some valence electrons with each of its neighbors, and it is therefore not possible to single out any given groups of atoms that may be regarded as chemically saturated. The quantitative discussion of such forces is not easy. ...
(d) Overlap. If two atoms approach so closely that their electron shells overlap, then there is a strong repulsive force between them. ...
(e) Metallic bond. ... it is worth noting that in the case of a metal the presence and motion of the conduction electrons is an important factor in holding the crystal together and in determining its structure.
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About Rudolf Peierls
Sir Rudolf Ernst Peierls (5 June 1907 – 19 September 1995) was a German-born British physicist, known as one of the pioneers of quantum mechanics. His honours include the Max Planck Medal in 1963, a British knighthood in 1968, the Copley Medal in 1986, and the Dirac Medal and Prize in 1991. Peierls played a major role in Tube Alloys, Britain's nuclear weapon programme, as well as the subsequent Manhattan Project, the combined Allied nuclear bomb programme.
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Native Name:
Rudolf Ernst Peierls
Alternative Names:
R.E. Peierls
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Sir Rudolf Ernst Peierls
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Sir Rudolph Ernst Peierls
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When I arrived in Leipzig, Heisenberg was working on the theory of ferromagnetism. It was known the magnetism of such substances as iron was due to the "spin" of the electrons inside the substance. Each electron spins like a little top, and in the iron there is a "molecular field", a force that tends to align the spin of each electron with that of its neighbors. But the nature of this field was unknown. It could not be a magnetic effect because magnetic forces are much too weak to account for the observed behaviour. Heisenberg saw that the answer lay in the Pauli exclusion principle, which says that no two electrons can be in exactly the same state. Thus two electrons with the same spin orientation keep out of each other's way; while this repulsion may increase their energy of motion, it diminishes their mutual repulsion, and can therefore lead to a decrease in total energy, making the parallel alignment of the electron spins energetically favourable. He had encountered this mechanism in the theory of atomic spectra and concluded that it was also responsible for ferromagnetism.
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With both light and electrons, one was faced with the so-called "wave-particle duality"; both could be regarded as waves for some purposes and as particles for others. An important step in resolving this paradox was a paper by Max Born in July 1926, in which he suggested that the waves determine the probability of finding the particle in a particular place. This idea was already considered much earlier by Einstein, but it was rejected by him. This interpretation of the theory was further developed in the spring of 1927 by Heisenberg, who formulated his "uncertainty principle" ...
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