In this post we are going to discuss about the alpha scattering experiment and nuclear model of the atom( describe the rutherford atomic model)
Experimental Arrangement:
D is the lead screen with a small hole in it to select a very fine beam of α-particles. This well collimated beam is then allowed to fall on a skinny(thin) gold foil F. While passing through the gold foil, the a-particles are scattered through different angles. A zinc sulphide screen was placed on the other aspect (side) of the gold foil. This screen was movable, so as to receive the α-particles, scattered from the gold foil at angles varying from zero to 180°. When an α-particle strikes the screen, it produces a flash of light and it is determined by the microscope M.
Result: It was found that:
(1) Most of the α-particles passed through the gold foil with small deviation.
(2) There were a few particles that were scattered through huge (large) angles. Experimental results showed that one of about 8000 particles suffered angles of scattering > 90°. A few of the α-particles were even scattered directly in the backward direction (i.e., angle of scattering = 180°). Thomson's atom model were failed to explain the experimental results. Therefore, Rutherford pictured an atom as follows.
Rutherford Nuclear Atom Model.
(1) The atom has a small, positively charged nucleus. All positive charges of an atom and most of the mass of the atom are focused in the nucleus. Electrons have no place inside the nucleus. The electrons revolve around this nucleus at some distance( long) away. The dimensions of the nucleus and of the electrons are small in comparison to the general length of the atom, so that maximum of the extent occupied via an atom is actually an empty space. Thus the discovery (invention) of the nucleus of the atom is because to Rutherford.
(2) Since the electron-distribution have to provide stability to the atom, the electrons couldn't be stationary. The electrons have to revolving across the nucleus in closed orbits, so that the centrifugal force because of the rotation of the electron is balanced by the force of electrostatic attraction between the nucleus and the electrons. As a result Rutherford proposed a dynamic planetary model where in nucleus plays the role of the sun and electrons correspond to the individual planets of the solar system.
Because maximum (most) of the atom is empty, most of the α-particles pass through the foil without considerable deflection. However, if an α-particle is moving in sort of path so as to have a head-on collision with the nucleus, the α-particle can be scattered through huge( large)angles. Sometimes, when a head-on collision occurs, the a-particle is turned back. Consequently the Rutherford's model of the nucleus enables us to account for very large (massive)deviations.
