Physics · Atoms · NEET
| Positive charge | Spread uniformly over the whole atom | Concentrated in a tiny central nucleus |
| Nucleus | No nucleus | Small, dense, positively charged nucleus |
| Electrons | Embedded inside like seeds in a watermelon | Revolve around the nucleus in empty space |
| Most of the atom | Filled with positive charge | Empty space |
| Explains alpha scattering | No, cannot explain large-angle scattering | Yes, large-angle scattering proves the nucleus |
| Year proposed | 1898 (earlier) | About 1911 (later) |
Yes. Thomson's model (1898) is the plum pudding model. NCERT describes it as positive charge spread uniformly through the whole atom with electrons embedded in it like seeds in a watermelon. So plum pudding, watermelon model and Thomson model all mean the same thing.
Because it could not explain the alpha-scattering experiment. If positive charge were spread out thinly over the whole atom, no alpha particle could feel a strong enough force to bounce back. But a few alpha particles bounced back through large angles. This is only possible if the positive charge is packed into a tiny hard nucleus, which is Rutherford's idea, not Thomson's.
He kept the atom neutral but changed where the positive charge sits. Thomson: positive charge spread over the full atom volume. Rutherford: almost all positive charge and nearly all mass squeezed into a tiny central nucleus, with electrons revolving around it in the mostly empty space outside.
No. There is no nucleus in Thomson's model. The positive charge is smeared uniformly through the atom. The idea of a small dense nucleus was introduced only by Rutherford after the alpha-scattering results.
Thomson's model came first (1898). Rutherford proposed his nuclear model later (around 1911) based on the Geiger-Marsden alpha-scattering experiment. So the order is Thomson then Rutherford.
Yes. Both models say the atom is electrically neutral, with equal amounts of positive and negative charge. They only disagree on how the positive charge is arranged: spread out (Thomson) versus concentrated in a nucleus (Rutherford).
Given below are two statements. Statement I: Atoms are electrically neutral as they contain equal number of positive and negative charges. Statement II: Atoms of each element are stable and emit their characteristic spectrum. Choose the most appropriate answer.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
The main difference is the position of the positive charge. Thomson spread it evenly over the whole atom (plum pudding), while Rutherford concentrated it in a tiny central nucleus with electrons revolving outside.
The Geiger-Marsden alpha-particle scattering experiment. A thin gold foil was bombarded with alpha particles. Most passed straight through, but a few bounced back through large angles, proving a small dense positive nucleus exists.
Because a spread-out positive charge gives only a weak, gentle force on an alpha particle. It cannot produce a strong enough repulsion to turn an alpha particle back through a large angle. A concentrated nucleus can, which is why Rutherford's model replaced it.
Yes. Both keep the atom electrically neutral with equal positive and negative charge. They differ only in how the positive charge is arranged inside the atom.
No. Rutherford's model correctly located the nucleus, but a classical revolving electron should spiral into the nucleus and give a continuous spectrum. Bohr's model later fixed these problems using quantised orbits.
