Rutherford’s planetary model of the

We urge you to keep Rutherford s planetary model of the atom (Section 1.4) in mind while reading this chapter. That model, with its consideration of the electrical forces within atoms and molecules, provides the foundation of the entire subject of chemical bonding and molecular structure. 

Rutherford s planetary model of the atom assumes that an atom of atomic number Z comprises a dense, central nucleus of positive charge +Ze surrounded by a total of Z electrons moving around the nucleus. The attractive forces between each electron and the nucleus, and the repulsive forces between the electrons, are described by Coulomb s law. We first discuss Coulomb s law in general terms, and then apply it to the planetary atom. 

Bohr supplemented Rutherford s planetary model of the atom with the assumption that an electron of mass moves in a circular orbit of radius r about a... 

Realizing that Rutherford s planetary model of the atom is incompatible with the classical Maxwell theory of radiation—which stipulates that a charged electron in circular motion will continually emit radiation and thereby lose energy, its orbit will shrink, and it will quickly spiral into the nucleus—Niels Bohr in 1913 (see Fig. 3.25) asserted that an electron in an atomic orbit simply does not radiate in other words Maxwell s theory does not apply at this level. Bohr s main contribution was to make two nonclassical assumptions. ... 

What Bohr understood about the nucleus he embodied in a landmark lecture to the Danish Academy on January 27, 1936, subsequently published in Nature, Neutron capture and nuclear constitution exploited the phenomenon of neutron capture to propose a new model of the nucleus once again, as he had with Rutherford s planetary model of the atom, Bohr stood on the solid ground of experiment to argue for radical theoretical change. 

The incompatibility of Rutherford s planetary model, based soundly on experimental data, with the principles of classical physics was the most fundamental of the conceptual challenges facing physicists in the early 1900s. The Bohr model was a temporary fix, sufficient for the interpretation of hydrogen (H) atomic spectra as arising from transitions between stationary states of the atom. The stability of atoms and molecules finally could be explained only after quantum mechanics had been developed. 

Dalton s atomic theory, nuclear model of the atom, planetary model of the atom, Rutherford s scattering experiment... 

Rutherford performed several calculations that led him to an inescapable conclusion the atom is made up mainly of empty space, with a small, massive region of concentrated charge at the centre. Soon afterward, the charge on this central region was determined to be positive, and was named the atomic nucleus. Because Rutherford s atomic model, shown in Figure 3.5 on the next page, pictures electrons in motion around an atomic nucleus, chemists often call this the nuclear model of the atom. You may also see it referred to as a planetary model because the electrons resemble the planets in motion around a central body. 

The nuclear concentration of mass anticipated Rutherford s model of the atom, and Bohr s planetary model by a decade. The spectral integers, linked to a standing-wave pattern, predates de Broglie s proposal by two decades. 

Einstein was not the only one to find Planck s concept useful. In the laboratory of J. J. Thomson, Niels Bohr was in conflict with his mentor over the proper model for an atom. Thomson adhered to his plum pudding model, and Bohr preferred the planetary model of Rutherford. Finally Thomson suggested that Bohr work with Rutherford (who by this time had relocated in Manchester), and Bohr obliged. 

Understanding of Earth history and geological materials has been greatly facilitated by the discovery of fundamental chemical principles. It has been more than 200 years since Dalton first theorized on the stracture of the atom and more than 100 years since Mendelev s 1870 version of the periodic table had reached the form close to that we use today. But it was Rutherford s 1911 planetary model and Neil Bohr s 1913 electrostatic model of the atom that allowed geologists to become geochemists and rigorously apply these new ideas to the study of the earth. 

What was true for Nagaoka s Saturnian atom was also true, theoretically, for the atom Rutherford had found by experiment. It the atom operated by the mechanical laws of classical physics, the Newtonian laws that govern relationships within planetary systems, then Rutherford s model should not work. But his was not a merely theoretical construct. It was the result of real physical experiment. And work it clearly did. It was as stable as the ages and it bounced back alpha particles like cannon shells. 

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