Bohr atom

Whereas zirconium was discovered in 1789 and titanium in 1790, it was not until 1923 that hafnium was positively identified. The Bohr atomic theory was the basis for postulating that element 72 should be tetravalent rather than a trivalent member of the rare-earth series. Moseley s technique of identification was used by means of the x-ray spectra of several 2ircon concentrates and lines at the positions and with the relative intensities postulated by Bohr were found (1). Hafnium was named after Hafma, the Latin name for Copenhagen where the discovery was made. 

To understand the origins of dispersion forces, let us consider two Bohr atoms, each of which consists of an electron orbiting around a nucleus comprised of a proton, having a radius ao, often referred to as the first Bohr radius . It is obvious that a Bohr atom has no permanent dipole moment. However, the Bohr atom can be considered to have an instantaneous dipole moment given by... 

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.

Whether the Bohr atomic model or the quantum mechanical model is introduced to students, it is inevitable that they have to learn, among other things, that (i) the atomic nucleus is surrounded by electrons and (ii) most of an atom is empty space. Students understanding of the visual representation of the above two statements was explored by Harrison and Treagust (1996). In the study, 48 Grade 8-10... 

The Bohr atom went a long way toward explaining the nature of atoms, but there were problems. Although scientists could calculate the emission spectrum of hydrogen using the Bohr model, the model could not account for the spectra of heavier atoms. The biggest problem with the Bohr atom, however, lay in its lack of a... 

The beautiful Bohr atomic model is, unfortunately, too simple. The electrons do not follow predetermined orbits. Only population probabilities can be given, which are categorized as shells and orbitals. The orbitals can only accommodate two electrons. Shells and orbitals can also merge ("hybridization"). In the case of carbon, the 2s orbital and the three 2p orbitals adopt a configuration in the shape of a tetrahedron. Each of these sp3 orbitals is occupied by one electron. This gives rise to the sterically directed four-bonding ability of carbon. 

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... 

M Astatine is isolated in tiny amounts from reactor materials. The Bohr atomic model shows the tightly packed electron shell. One can formally see" the instability. It was the last of the 92 naturally occurring elements to be found. 

Niels Bohr, "On the Constitution of Atoms and Molecules, Pt.I, Binding of Electrons by Positive Nuclei," PhiLMag. 26 (1913) 125 Pt. II, "Systems Containing Only a Single Nucleus," Phil.Mag. 26 (1913) 476502 "Pt. Ill, Systems Containing Several Nuclei," Phil.Mag. 26 (1913) 857875. See John Heilbron and Thomas Kuhn, "The Genesis of the Bohr Atom," HSPS 1 (1969) 211290. 

Ibid., 122, 130, 138 Bohr, "On the Constitution of Atoms and Molecules." And John Heilbron and Thomas Kuhn, "The Genesis of the Bohr Atom," 245250. 

Bohr s hydrogen atom model of 1913 had provided inspiration to a few physicists, like Kossel, who were interested in chemical problems but to very few chemists concerned with the explanation of valence. First of all, the Bohr atom had a dynamic character that was not consistent with the static and stable characteristics of ordinary molecules. Second, Bohr s approach, as amended by Kossel, could not even account for the fundamental tetrahedral structure of organic molecules because it was based on a planar atomic model. Nor could it account for "homopolar" or covalent bonds, because the radii of the Bohr orbits were calculated on the basis of a Coulombic force model. Although Bohr discussed H2, HC1, H20, and CH4, physicists and physical chemists mainly took up the problem of H2, which seemed most amenable to further treatment. 11... 

Rutherford-Bohr Atom." American Journal of Physics 49 (1981) 223231. 

Explain how the Bohr atomic model differs from the Rutherford atomic model, and explain the observations and inferences that led Bohr to propose his model. 

Both the Rutherford and Bohr atomic models have been described as planetary models. In what ways is this comparison appropriate In what ways is this comparison misleading ... 

Quantitative treatment of the interaction between two identical Bohr atoms, consisting of point electrons and nuclei, leads to an expression which, apart from a numerical factor, is the same as that derived quantum-mechanically by London (1937) ... 

Electrons Changing Energy Level in the Bohr Atom... 

In the Bohr atom, as it is commonly now depicted, electrons -which have a mass just 0.00055 times that of the proton, but an equal and opposite electric charge - orbit around a nucleus of protons and neutrons, packed together with an awesome density. If matter were uniformly as dense as the nucleus rather than containing so much empty space, a thimbleful would weigh about a billion tonnes. ... 

Which is all very well, but the Bohr atom is wrong. The picture of a dense nucleus surrounded by electrons is accurate enough, but they do not follow nice elliptical orbits like those of the planets. Venus and Mars follow Newton s laws, but electrons are governed by the... 

Born, M. and Lande, A. (1918). [The absolute calculation of crystal properties with the aid of the Bohr atom model]. Sitsungsber. Preuss. Akad. Wissen. Berlin 45, 1048-68 (in German). 

Fio. 2-3.—At the left is represented the circular orbit of the Bohr atom. At the right is shown the very eccentric orbit (line orbit), with no angular momentum, that corresponds somewhat more closely to the description of the hydrogen atom in its normal state given by quantum mechanics. 

The first attempts to interpret Werner s views on an electronic basis were made in 1923 by Nevil Vincent Sidgwick (1873—1952) and Thomas Martin Lowry (1874—1936).103 Sidgwick s initial concern was to explain Werner s coordination number in terms of the sizes of the sub-groups of electrons in the Bohr atom.104 He soon developed the attempt to systematize coordination numbers into his concept of the effective atomic number (EAN).105 He considered ligands to be Lewis bases which donated electrons (usually one pair per ligand) to the metal ion, which thus behaves as a Lewis acid. Ions tend to add electrons by this process until the EAN (the sum of the electrons on the metal ion plus the electrons donated by the ligand) of the next noble gas is achieved. Today the EAN rule is of little theoretical importance. Although a number of elements obey it, there are many important stable exceptions. Nevertheless, it is extremely useful as a predictive rule in one area of coordination chemistry, that of metal carbonyls and nitrosyls. 

The angular momentum or an electron moving in an orbit of the type described by Bohr is ail axial vector L = r x p, formed from the radial distance r between electron and nucleus and the linear momentum p of the electron relative lo a fixed nucleus. Figure 2 shows the customary method used to illustrate the axial vector L in terms of the orbital morion of any object, of which the electron of the Bohr atom is only one example. Although Bohr s planetary model needed only circular orbits lo explain the spectral lines observed in the spectrum of a hydrogen atom, subsequent... 

While the Bohr atom is of no help in understanding the splittings of the Balmer lines, using it we can calculate the field at which a state is ionized by an electric field. Consider a H atom with its nucleus at the origin in the presence of an electric field in the z direction. The potential experienced by an electron moving along the z axis is given by... 

When Eq. 2.19 was applied to the Bohr atom a most amazing answer was obtained. Combination of Eqs. 2.7 and 2.17 gave, for the electron velocity... 

---