Atoms MCQs for NEET — Physics Questions with Answers

The NCERT states, 'A classical atom based on Rutherford’s model is doomed to collapse.' This is because electrons revolving around the nucleus are accelerating and, according to classical electromagnetism, should continuously radiate energy and spiral into the nucleus, thus experiencing a net force.

According to the NCERT summary for Rutherford's model: 'most of the mass of the atom and all its positive charge are concentrated in a tiny nucleus'.

The NCERT states, 'This model in which mass of the atom is considered to be evenly spread over the atom was proved wrong by Rutherford’s famous alpha-particle scattering experiment in 1909.' Rutherford's experiment indicated a highly non-uniform distribution with a central, dense nucleus.

The NCERT chapter 'Atoms' summary explicitly mentions Rutherford nuclear model's difficulty: 'It predicts that atoms are unstable because the accelerated electrons revolving around the nucleus must spiral into the nucleus. This contradicts the stability of matter.'

The exercise question asks: 'The size of the atom in Thomson’s model is .......... the atomic size in Rutherford’s model. (much greater than/no different from/much less than.)'. The answer given in the context (implied by the solution of such questions) is 'no different from'. While the internal structure differs, both models attempt to describe the overall size of the atom as roughly $10^{-10}$ m.

The NCERT states, 'This model was picturesquely called plum pudding model of the atom.' and also directly attributes this description to Thomson's model: 'Thomson in 1898 proposed that an atom consists of uniform sphere of positive electricity with electrons embedded into it. This model in which mass of the atom is considered to be evenly spread over the atom...'

The exercise question implies this: 'In the ground state of __________ electrons are in stable equilibrium, while in __________ electrons always experience a net force.' The correct choice for stable equilibrium is Thomson's model, where electrons are statically embedded. In Rutherford's model, electrons are constantly accelerating, experiencing a net force.

The NCERT text says, 'Rutherford’s model of atom resembles the solar system in which the nucleus plays the role of sun and the electrons that of revolving planets.'

The NCERT states, 'Further, it was also silent about the electronic structure of atoms i.e., about the distribution and relative energies of electrons around the nucleus. The difficulties of the Rutherford model were overcome by Niels Bohr in 1913 in his model of the hydrogen atom.'

The NCERT explicitly mentions, 'According to this model, the positive charge of the atom is uniformly distributed throughout the volume of the atom and the negatively charged electrons are embedded in it like seeds in a watermelon.'