DISCOVERY OF NUCLEUS
Ruther ford’s experiments of scattering of alpha particles lead to the discovery of Nucleus in 1911.
Before this in 1906 Rutherford’s had discovered that alpha particles were actually Helium atoms with its two electrons removed, thus giving it a double positive charge (He+2).
Rutherford bombarded a very thin gold metal foil with alpha particles from a radioactive source and strike the gold metal foil. He observed that most of the particles went straight through the foil. Very few particles deflected at various angles and only a few deflected back at the same path at which they had striked. The particles were detected on a zinc sulfide (Zns) fluorescent.
Keeping in view the above experiments, Ruther ford suggested that the region at which the particles had deflected had heavy mass .As most of the particles passed through the foil, thus he suggested that most of the atom is composed of ”empty space” the region that caused deflection was called as nucleus . The Rutherford experiment can be described in the diagram given below:
Keeping in view the observation from the above experiment Ruther ford suggested a model for an atom, called as RUTHER FORD ATOMIC MODEL.
RUTHER FORD ATOMIC MODEL:.
Rutherford proposed a model of an atom and considered it similar to the solar system.
- Atom is composed of a heavy region, which is positively charged and contain whole of its mass. (Proton+ Neutron). This region is called as nucleus.
- The nucleus is surrounded by electrons. The number of electrons are equal to number of proton in the nucleus.
- The electrons are in constant motion around the nucleus. The electrostatic force of attraction between electrons and protons provides the centripetal force.
DEFECTS IN RUTHER FORD ATOMIC MODEL:.
- The laws of gravitation and laws of motion could be applied to the neutral bodies like plants, but not to the charged bodies, such as protons and Electron.
- According to Maxwell theory and laws of physics, a charge body like electron revolving around the nucleus should radiate energy continuously and will move in a spiral path resulting in a collapse of atom, which does not happen and atom is stable, as shown in fig:
- There were no define orbits for electrons.
If electron radiate energy continuously them continuous spectrum should be formed, instead of this line spectrum is obtained for elements.
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