2-5: Rutherford's Atomic Model |
| As discussed in the preceding page, we should consider that Thomson's raisin bread model (plum pudding model) was unsuccessful, because it could not explain the results of the alpha particle scattering experiment of Geiger and Marsden.
Let us look back upon the experimental results; we can summarize them as follows:
[The Results of Geiger and Marsden's experiment] |
| (1) | Almost all the incident alpha particles go straight and are scarcely scattered. |
| (2) | Only occasionally such a large-angle scattering through an angle greater than 90 degrees or near 180 degrees occurs. |
| (3) | The scattering rate (or probability) depends on the atomic weight of the target; the more the atomic weight, the larger the probability. |
| [The Rutherford Model of the Nuclear Atom]
Considering the results of Geiger and Marsden's experiment and the failure of Thomson's atomic model, E. Rutherford (UK, 1871 - 1937) proposed a model in which the electric charge +Ze in an atom is not distributed over the whole area of the atom but concentrates in a small area (1911).
He thought as follows: The charge +Ze is localized to be a cluster or a group and the alpha particle is scattered by Coulomb's repulsive force, (C. A. de Coulomb: France, 1736 - 1806). Namely, his idea is that the large-angle scattering of the alpha particle is brought about by a single scattering due to Coulomb's repulsive force between the charge of the alpha particle, +2e, and that of the cluster, +Ze. The cluster is called atomic nucleus or simply nucleus. Rutherford's atomic model is often called Rutherford model or sometimes Rutherford model of the nuclear atom.
A schematic image of the Rutherford model is shown in the following figure, where a black big ball at the center is the nucleus and small red points moving around the nucleus are electrons. |
| | The Rutherford Model of the Nuclear Atom
A black big ball at the...