Which of the following is NOT a difference between Thomson’s model and Rutherford’s model of the atom?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Neutrons are present inside the nucleus.
In Thomson’s plum pudding model the positive charge is spread uniformly through the atom with the electrons embedded in it. In Rutherford’s nuclear model the positive charge and most of the mass sit in a tiny nucleus, with the electrons moving in orbits around it.
Option (1) Neutrons are present inside the nucleus. — Not a difference. Neither model has neutrons. Thomson’s model (1898) and Rutherford’s model (from the 1911 scattering experiments) both came before Chadwick discovered the neutron in 1932. So this is not a point on which the two models differ.
Option (2) The positive charge is concentrated in a tiny nucleus. — A difference. Rutherford placed the whole positive charge in a tiny nucleus. Thomson spread it uniformly through the whole atom.
Option (3) The electrons must be in motion inside the atom. — A difference. In Rutherford’s model the electrons revolve around the nucleus. The Coulomb attraction gives the centripetal force. In Thomson’s model they are embedded in the positive charge like seeds in a watermelon.
Option (4) The mass of the atom is spread uniformly through the atom. — A difference. This picture of a uniform atom belongs to Thomson’s model. In Rutherford’s model most of the mass is concentrated in the nucleus.
NCERT (2026-27):
Introduction – “The first model of atom was proposed by J. J. Thomson in 1898.”
Alpha-particle Scattering and Rutherford’s Nuclear Model of Atom – “At the suggestion of Ernst Rutherford, in 1911, H. Geiger and E. Marsden performed some experiments.”
Discovery of Neutron – “Since the nuclei of deuterium and tritium are isotopes of hydrogen, they must contain only one proton each. … This hypothesis was verified in 1932 by James Chadwick who observed emission of neutral radiation when beryllium nuclei were bombarded with alpha-particles …. The clue to this puzzle, which Chadwick satisfactorily solved, was to assume that the neutral radiation consists of a new type of neutral particles called neutrons.”