Describe the observation in the Alpha particle scattering experiment which lead Rutherford to make the following conclusion
(i) Nucleus is positively charged.
(ii) Almost an entire mass of an atom is present in the nucleus of the atom.
(iii) Most of the space in an atom is empty.
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Solution
In 1911, Ernest Rutherford and his co-workers carried out a series of experiments using alpha particles. A beam of alpha particles was directed against a thin foil of about 0.0004 cm thickness of gold, platinum, silver, or copper respectively. The foil was surrounded by a circular fluorescent zinc sulfide screen. Whenever an a-particle struck the screen, it produced a flash of light.
The following observations were made:
Most of the a-particles (nearly 99%) went straight without suffering any deflection,
A few of them got deflected through small angles.
A very few (about one in 20,000) did not pass through the foil at all but suffered large deflections (more than 90°) or even came back in more or less the direction from which they have come,(deflection of 180°).
(i) A few of the a-particles were deflected from their original paths through moderate angles; it was concluded that the whole of the positive charge is concentrated.
(ii) The space occupied by this positive charge is very small in the atom. When a-particles come closer to this point, they suffer a force of repulsion and deviate from their paths. The positively charged heavy mass which occupies only a small volume in an atom is called the nucleus. It is supposed to be present at the centre of the atom.
(iii) Since, most of the alpha particles went straight through the metal foil un-deflected, it means that there must be a very large empty space within the atom or the atom is extraordinarily hollow.
