Atomic structure Bohr atom

Models of nuclei have grown in sophistication as new discoveries about subatomic particles have been made. One of the simplest was suggested by Niels Bohr, the Danish scientist who contributed a great deal to our understanding of atomic structure. Bohr compared the nucleus to a drop of liquid. His liquid drop model proposes that nucleons are packed together like the molecules in a liquid. Nucleons at the surface of the... 

Finally, an explanation was provided in 1913 by Niels Bohr (1885-1962), a Danish physicist who tackled the problem of trying to understand fundamental atomic structure. Bohr postulated that the electron in hydrogen travels around the nucleus in the manner in which a planet orbits the Sun. Hence his model was called the planetary model. The important distinction between the orbit of a planet around the Sun and the orbit of an electron around a nucleus is that the distance of a planet from the Sun is arbitrary, whereas in the Bohr model an electron cannot exist at just any distance from a nucleus. An electron can orbit the nucleus only at particular fixed, or discrete, distances from the nucleus. 

Old and new values for-structure variables, in atomic units (bohrs and radians]... 

The concept of chemical periodicity is central to the study of inorganic chemistry. No other generalization rivals the periodic table of the elements in its ability to systematize and rationalize known chemical facts or to predict new ones and suggest fruitful areas for further study. Chemical periodicity and the periodic table now find their natural interpretation in the detailed electronic structure of the atom indeed, they played a major role at the turn of the century in elucidating the mysterious phenomena of radioactivity and the quantum effects which led ultimately to Bohr s theory of the hydrogen atom. Because of this central position it is perhaps not surprising that innumerable articles and books have been written on the subject since the seminal papers by Mendeleev in 1869, and some 700 forms of the periodic table (classified into 146 different types or subtypes) have been proposed. A brief historical survey of these developments is summarized in the Panel opposite. 

The discovery of hafnium was one of chemistry s more controversial episodes. In 1911 G. Urbain, the French chemist and authority on rare earths , claimed to have isolated the element of atomic number 72 from a sample of rare-earth residues, and named it celtium. With hindsight, and more especially with an understanding of the consequences of H. G. J. Moseley s and N. Bohr s work on atomic structure, it now seems very unlikely that element 72 could have been found in the necessary concentrations along with rare earths. But this knowledge was lacking in the early part of the century and, indeed, in 1922 Urbain and A. Dauvillier claimed to have X-ray evidence to support the discovery. However, by that time Niels Bohr had developed his atomic theory and so was confident that element 72 would be a... 

N. Bohr (Copenhagen) investigations of the structure of atoms, and of the radiation emanating from them. 

A. Bohr (Copenhagen), B. Mottelson (Copenhagen) and J. Rainwater (New York) discovery of the connection between collective motion and particle motion in atomic nuclei and the development of the theory of the structure of the atomic nucleus based on this connection. 

In this paper, the electronic structure of disordered Cu-Zn alloys are studied by calculations on models with Cu and Zn atoms distributed randomly on the sites of fee and bcc lattices. Concentrations of 10%, 25%, 50%, 75%, and 90% are used. The lattice spacings are the same for all the bcc models, 5.5 Bohr radii, and for all the fee models, 6.9 Bohr radii. With these lattice constants, the atomic volumes of the atoms are essentially the same in the two different crystal structures. Most of the bcc models contain 432 atoms and the fee models contain 500 atoms. These clusters are periodically reproduced to fill all space. Some of these calculations have been described previously. The test that is used to demonstrate that these clusters are large enough to be self-averaging is to repeat selected calculations with models that have the same concentration but a completely different arrangement of Cu and Zn atoms. We found differences that are quite small, and will be specified below in the discussions of specific properties. 

Fig. 7. Maps of the electronic charge density in the (110) planes In the ordered twin with (111) APB type displacement. The hatched areas correspond to the charge density higher than 0.03 electrons per cubic Bohr. The charge density differences between two successive contours of the constant charge density are 0.005 electrons per cubic Bohr. Atoms in the two successive (1 10) planes are denoted as Til, All, and T12, A12, respectively, (a) Structure calculated using the Finnis-Sinclair type potential, (b) Structure calculated using the full-potential LMTO method.

The hydrogen atom, containing a single electron, has played a major role in the development of models of electronic structure. In 1913 Niels Bohr (1885-1962), a Danish physicist, offered a theoretical explanation of the atomic spectrum of hydrogen. His model was based largely on classical mechanics. In 1922 this model earned him the Nobel Prize in physics. By that time, Bohr had become director of the Institute of Theoretical Physics at Copenhagen. There he helped develop the new discipline of quantum mechanics, used by other scientists to construct a more sophisticated model for the hydrogen atom. 

Bohr s quantum numbers (n, l, m) have fully entered chemistry, and every chemistry student learns about the symbols Is, 2s, 2p, 3s, 3p, 3d etc. It is hence a startling fact that the simple energy rule has not entered any major chemistry textbooks, as far as I know, and it is still this rule which gives the first explanation of the occurrence of the transition metals, the rare-earth metals, and the over-all structure of the electronic shells of atoms, (p.334). 

The energy rule for the neutral atoms was obviously in contradiction to Bohr s calculation on the hydrogen atom, which indicated that the energies should be increasing with increasing n. It is typical of the nature of "frontier-research" that Bohr abandoned this rule for the higher atoms, since it led to the wrong structure of the periodic system, and the modified rule [(n + , n)] seems to have... 

Moseley photographed characteristic spectra for some 38 elements that could serve as x-ray tube targets. In two papers,37 he not only uncovered structure in the K and L spectra—he alscr established the atomic number as more fundamental than the atomic weight, and he provided brilliant support for- the Bohr theory of atomic structure. 

In recent years the old quantum theory, associated principally with the names of Bohr and Sommerfeld, encountered a large number of difficulties, all of which vanished before the new quantum mechanics of Heisenberg. Because of its abstruse and difficultly interpretable mathematical foundation, Heisenberg s quantum mechanics cannot be easily applied to the relatively complicated problems of the structures and properties of many-electron atoms and of molecules in particular is this true for chemical problems, which usually do not permit simple dynamical formulation in terms of nuclei and electrons, but instead require to be treated with the aid of atomic and molecular models. Accordingly, it is especially gratifying that Schrodinger s interpretation of his wave mechanics3 provides a simple and satisfactory atomic model, more closely related to the chemist s atom than to that of the old quantum theory. 

Fig. 1. Comparison of experimental values (solid curves) and predicted values (dashed lines) of the saturation ferromagnetic moment per atom, in Bohr magnetons, for Fe-Co, Co-Ni, and Ni-Cu alloys. The short vertical lines indicate change in crystal structure (from Ref. (2)).

The capacity to solve novel problems by constructing analogies to already-used visualisations. (Gilbert, 2008). For example, using Kepler s model of the Solar System to explain the electronic structure of an atom, in the manner of Bohr, and hence being able to predict, very approximately, the absorption spectram that it will produce. 

The last big problem facing early twentieth century physics was Ernest Rutherford s atomic structure. Physicists knew that Rutherford s atom could not exist, but no one could come up with anything better. The man who would resolve this conundrum showed up at Manchester, England, in 1912 to work for Rutherford. Rutherford himself had worked for J.J. Thomson and had disproved Thomson s plum pudding structure of the atom. Now, the new man in Manchester, Niels Bohr, was about to do the same thing to Rutherford. By the end of his career, Bohr would have contributed as much as anyone to understanding Feynman s little particles. Science is a meritocracy. Poor kids can excel and get ahead in the world of science just as easily as the well-heeled. For example. 

By the 1930s, the structure of the atom worked out by Rutherford, Bohr, and others had answered the pressing questions fac-... 

The shells play a leading role in the structure of the Periodic Table. This graphic representation is borrowed from the Bohr atomic model. Historically, the shells were assigned letters, nowadays... 

The first steps toward the understanding of the nature of the chemical bond could not be taken until the composition and structure of atoms had been elucidated. The model of the atom that emerged from the early work of Thomson, Rutherford, Moseley, and Bohr was of... 

The first plausible theory of the electronic structure of the atom was proposed in 1914 by Niels Bohr (1885-1962), a Danish physicist. In order to explain the hydrogen spectrum (Fig. 17-1), he suggested that in each hydrogen atom, the electron revolves about the nucleus in one of several possible circular orbits, each having a definite radius corresponding to a definite energy for the electron. An electron in the orbit closest to the nucleus should have the lowest energy. With the... 

Bohr theory the first theory of atomic structure which involved definite internal energy levels for electrons. 

The carbon atom has, outside its nucleus, six electrons which, on the Bohr theory of atomic structure, were believed to be arranged in orbits at increasing distance from the nucleus. These orbits corres-... 

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