Rutherford, "planetary" model

The "orbital" concept is not precisely defined and according to Coulson [4] is a relic from the Bohr-Rutherford planetary model of the atom ... 

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. 

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 ... 

The planetary model of the atom was proposed by Rutherford in 1912 following the a particle scattering experiments of Geiger and Marsden, which showed most the mass of an atom to be concentrated in a tiny positive nucleus. The orbiting of light electrons resembles the problem of planetary motion first solved by Newton. 

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. 

By the early twentieth century, chemists and physicists recognized that the atoms of which chemical elements are composed are themselves made up of electrons and protons, of electrically negative and positive subatomic particles that were the universal constituents of all chemical elements. Sir Joseph Thomson had discovered the electron in 1897. Ernest Rutherford postulated the existence of a positive nucleus in atoms in 1911, and he used this in developing his planetary model of the atom, with a positive center and orbiting electrons. He discovered the proton in 1919, in experiments on the disintegration of atomic nuclei. Much later, in 1932, the British physicist James Chadwick (1891— 1974) discovered a third subatomic particle, the electrically neutral neutron. 

Rutherford proposed a model of the atom in which the charge on the nucleus was +Ze, with Z electrons surrounding the nucleus out to a distance of about 10 ° m (0.1 nm). The Rutherford model for a gold atom has 79 electrons (each with a charge of —le) arranged about a nucleus of charge +79e. The electrons occupy nearly the entire volume of the atom, whereas nearly all its mass is concentrated in the nucleus this model is often called the planetary model. ... 

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... 

I he atom is the most fundamental concept in the science of chemistry. A chem- I ical reaction occurs by regrouping a set of atoms initially found in those molecules called reactants to form those molecules called products. Atoms are neither created nor destroyed in chemical reactions. Chemical bonds between atoms in the reactants are broken, and new bonds are formed between atoms in the products. We have traced the concept of the atom from the suppositions of the Greek philosophers to the physics experiments of Thomson and Rutherford and we have arrived at the planetary model of the atom. We have used the Coulomb force and potential energy laws describing the interactions among the nucleus and the electrons in the planetary atom to account for the gain and loss of electrons by atoms,... 

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. 

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 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. 

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. 

Alpha particles bounced back, Rutherford reasoned, because the atom is not a pudding. The atom is mostly empty space with an incredibly small, incredibly dense, positively charged core. Rutherford proposed a new model—the planetary model—in which negatively charged electrons in huge orbits circled a tiny, dense, positively charged nucleus. 

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. 

In 1911, Rutherford proposed his planetary model of the atom in which the electrons revolved about the nucleus in various orbits, just as the planets revolve about the sun. However, there is a fundamental difficulty with this model. According to classical... 

Planetary model of the atom Rutherford scattering experiments... 

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

Describe the activity of electrons according to the planetary model of the atom that appeared after the Rutherford scattering... 

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