Describe Rutherford atom model. What are the draw backs of this model?

Describe Rutherford atom model. What are the draw backs of this model?


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8 years ago
Postulates: The experiments carried out by Geiger and Marsden gave rise to the Rutheroford’s
nuclear model of atom. This model of the atom is also known as Rutherford’s planetary model
of the atom. This model is based on the following postulates.
i) The whole of the positive charge and nearly the entire mass of the atom is concentrated in a
very small volume of the atom called nucleus. The nuclear radius is about (1/10,000) of the
atomic radius.
(ii) The electrons are distributed around the nucleus. So, there is lot of empty space in the
(iii) The amount of positive charge in the nucleus is equal to the amount of negative charge on
the electrons. So, the atom, as a whole, is an electrically neutral entity.
(iv) Electrons were continuously revolving around the nucleus in circular orbits. The
electrostatic force of attraction provides the necessary centripetal force.
Merits (i) Large angle scattering of alpha-particles through thin foils could be explained.
(ii) The classification of elements in the periodic table on the basis of their atomic number,
instead of atomic weight, was justified.
Limitations: (i) According to the classical electromagnetic theory, a charged particle in
accelerated motion should radiate energy in the form of electromagnetic radiation. As a result
of continuous emission of radiation, the energy of the electron should gradually decrease. This
should lead to a constant decrease in the radius of the electronic orbit. In other words, the
electron should follow a spiral path (as shown in figure) and finally fall into the nucleus. This
would mean a collapse of atomic structure. But the atom is a very stable structure. Thus,
Rutherford model fails to account for the stability of the atom.
(ii) Rutherford model does not envisage any particular values of the radius of the electronic
orbit. This should mean that an electron can emit radiations of all possible frequencies. In
other words, an atom should have a continuous radiation spectrum. But this is contrary to the
experimental result. The spectrum of an atom is a series of sharp lines. Thus, Rutherford
model could not explain the line spectra of the atoms

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