Given below are two statements:
Statement I : Most of the mass of the atom and all its positive charge are concentrated in a tiny nucleus and the electrons revolve around it, is Rutherford's model.
Statement II : An atom is a spherical cloud of positive charges with electrons embedded in it, is a special case of Rutherford's model.
In the light of the above statements, choose the most appropriate from the options given below

Solution

Physics sir · 4 steps

Name the model behind each picture: tiny nucleus is Rutherford, spread-out positive cloud is Thomson.

1. Statement I. Rutherford's gold foil experiment showed that most alpha particles pass straight through, while a few bounce back sharply. That needs all the positive charge and nearly all the mass packed into a tiny nucleus, with electrons revolving around it. So Statement I describes Rutherford's model correctly: true.
2. Statement II. A sphere of positive charge with electrons embedded in it is Thomson's plum pudding model. Thomson proposed it before Rutherford. Rutherford's experiment then ruled it out, because spread-out charge cannot produce large-angle scattering.
3. Not a special case. The two models contradict each other on where the positive charge sits: concentrated at the centre versus spread through the whole atom. Rutherford's model does not contain Thomson's as a special case, so Statement II is false.
4. So. Statement I is true and Statement II is false, which is option (b).

The idea to keep. Thomson: positive charge spread over the whole atom. Rutherford: positive charge squeezed into a tiny nucleus. Rutherford's experiment disproved Thomson's model, so neither is a special case of the other.

Answer from the NTA final answer key. Solution by PrepWiser.