Rutherfords Atom

The structure of the Rutherford atom was published in 1911. The new structure neatly fit the existing data, and it resembled a familiar arrangement the solar system (Figure 1.4). Finally, two millennia after Democritus proposed the existence of atoms, scientists knew what Feynmans little particles looked like. Unfortunately, there was... 

Ernest Rutherfords proposed atomic structure added to the problems posed to nineteenth century physics by the ultraviolet catastrophe and the photoelectric effect. Rutherfords atom had a negatively charged electron circling a positively charged nucleus. The physics of the day predicted that the atom would emit radiation, causing the electron to lose energy and spiral down into the nucleus. Theory predicted that Rutherfords atom could not exist. Clearly, science needed new ideas to explain these three anomalies. 

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. 

Students will demonstrate an understanding of the five basic atomic theories—the Dalton atom, the Thomson atom, the Rutherford atom, the Bohr atom, and the Schrodinger electron cloud model—and illustrate this understanding in a two-dimensional work of art. 

The nuclear theory of atomic structure, put forward by Rutherford, regarded the electrons as moving in orbits round the nucleus. The dynamical theory of this system was developed by Bohr, who found it necessary to supplement classical mechanics by the quantum mechanics of Planck. According to classical theory, a system consisting of an electron moving in a circular orbit round a nucleus, to which it is attracted according to Coulomb s law, would lose energy, with the result that the electron would approach and finally collide with the nucleus. Thus on the basis of classical theory, the Rutherford atom would only be stable for about io seconds, after which time the electron would have fallen into the nucleus. 

Rutherfords Atomic Model According to this model atom consists of two parts (i) nucleus and (ii) extra-nudear part. 

The Rutherford atom. The nuclear charge (n+) is balanced by the presence of n electrons moving in some way around the nucleus. 

Later Bohr would develop far more elaborately the idea of mutual limitations as a guide to greater understanding. It would supply a deep philosophical basis for his statecraft as well as for his physics. In 1913 he first demonstrated its resolving power. It was clear, he remembered at the end of his life, and that was the point about the Rutherford atom, that we had something from which we could not proceed at all in any other way than by radical change. And that was the reason then that [I] took it up so seriously. ... 

To preserve electrical neutrality in the Rutherford atom the numher of electrons will be equal to the number of protons in the nucleus (the atomic number). 

Atomic structure, (a) In 1895, P. Lenard detected electrons outside a thin glass tube in which they were produced, and concluded that the atoms in the glass must have a very open structure. Explain these results in terms of the Rutherford atom, (b) Describe the fundamental difiEierences among the Dalton, Thomson, Rudierfbrd, and Schrodinger models of the atom. 

Calculate (a) the repulsion force between the 2 negative spheres, (b) the force of attraction of the positive sphere for each negative sphere. Which force is greater What statement can you make about the stabilization of the Rutherford atom by electrostatic forces only ... 

Alternatively, if the author is thinking of an open-ended question, such as whether Bohr s theory resolved the question of the collapse of the Rutherford atom, then many might respond that there may be more than one answer. As in the previously considered case, one does not need to be a constructivist to accept the entries in the right-hand column under certain circumstances. But to claim that knowledge is constructed in general, or that the majority of exam questions have more than one answer is, 1 think, the height of folly. 

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