Explain Rutherford Model of Atom.
Answers
1. The major features of the Rutherford atomic model are as follows.
All protons are present inside the nucleus, which is situated at the centre of the atom.
Electrons reside outside the nucleus and revolve around the nucleus in well-defined orbits.
The size of the nucleus is very small in comparison to the size of an atom. As per Rutherford’s calculations, the size of the nucleus is 105 times smaller than an atom.
As the mass of the electron is negligible in comparison to the mass of the proton, almost all the mass of the atom is concentrated in the nucleus.
2. Drawbacks of Rutherford’s model are listed below:
Rutherford’s model failed to explain stability of atoms. According to Rutherford’s model, electrons are revolving around the nucleus. This means, electrons would be in a state of acceleration all the time. Since electrons are charged particles, therefore, electron revolving in a circular orbit should continuously emit energy. It is because whenever a charged particle is accelerated it emits energy. As a result of this, revolving electron would lose energy and would slow down. So, it would no longer be able to resist the attractive force of the nucleus. Hence, it would move closer and closer to the nucleus and would finally fall into the nucleus by following a circular path. This means atom should collapse but actually we know atom is stable.
Rutherford’s model does not explain the distribution of electrons around the nucleus.
Rutherford’s model does not tell anything about the energy of electrons.
Hi!
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.
Explanation:
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.
Most alpha particles were observed to pass straight through the gold foil, which implied that atoms are composed of large amounts of open space. Some alpha particles were deflected slightly, suggesting interactions with other positively charged particles within the atom. Still other alpha particles were scattered at large angles, while a very few even bounced back toward the source. (Rutherford famously said later, “It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.”) Only a positively charged and relatively heavy target particle, such as the proposed nucleus, could account for such strong repulsion. The negative electrons that balanced electrically the positive nuclear charge were regarded as traveling in circular orbits about the nucleus. The electrostatic force of attraction between electrons and nucleus was likened to the gravitational force of attraction between the revolving planets and the Sun. Most of this planetary atom was open space and offered no resistance to the passage of the alpha particles.
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