Describe the model of atom proposed by Rutherford.
Answers
Explanation:
Rutherford model, also called nuclear atom or planetary model of the atom, description of the structure of atoms proposed (1911) by the New Zealand-born physicist Ernest Rutherford. The model described the atom as a tiny, dense, positively charged core called a nucleus, in which nearly all the mass is concentrated, around which the light, negative constituents, called electrons, circulate at some distance, much like planets revolving around the Sun.
The nucleus was postulated as small and dense to account for the scattering of alpha particles from thin gold foil, as observed in a series of experiments performed by undergraduate Ernest Marsden under the direction of Rutherford and German physicist Hans Geiger in 1909. A radioactive source capable of emitting alpha particles (i.e., positively charged particles, identical to the nucleus of the helium atom and 7,000 times more massive than electrons) was enclosed within a protective lead shield. The radiation was focused into a narrow beam after passing through a slit in a lead screen. A thin section of gold foil was placed in front of the slit, and a screen coated with zinc sulfide to render it fluorescent served as a counter to detect alpha particles. As each alpha particle struck the fluorescent screen, it would produce a burst of light called a scintillation, which was visible through a viewing microscope attached to the back of the screen. The screen itself was movable, allowing Rutherford and his associates to determine whether or not any alpha particles were being deflected by the gold foil.
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What Is Rutherford Atomic Model?
▪Chadwick performed the same experiment of Rutherford but with beryllium/boron sheet few years after Rutherford’s.
▫He found that new particles carrying no charge and mass almost equal to proton were emitted. This neutral particle is known as neutron.
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Rutherford suggested an atomic model based upon his scattering experiment and the discovery of neutrons:-
a) An atom has a minute and positively charged body at its centre known as nucleus. According to him, nucleus contains all the protons and neutrons of the atom. As protons and neutrons constitute most of the mass of the atom, most of the mass of the atom resides in nucleus.
b)To balance the positive charge of the protons present inside the nucleus, there are present electrons distributed around the nucleus.
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**He further explained the reason for electron not falling in to the nucleus in spite of the mutual electrostatic forces of attraction between the electron outside and the protons inside the nucleus.**
He proposed that the electrons are revolving at such a high velocity that the centrifugal force acting outwards balances the electrostatic forces of attraction acting inwards and due to the same reason, electrons do not fall in to the nucleus.