On an experimental basis, Ernest Rutherford proved in 1911 that J.J. Thomson’s so-called “plum-pudding model” was incorrect.
Rutherford’s alpha-particle Scattering Experiment
The key points or inferences drawn from Rutherford’s experiment, on which he based his model of the atom were as follows:
- The atom is 99.9% empty space.
- Most of the positive charge of the atom is concentrated in a tiny, dense volume at the center of the atom. This is known as the nucleus of the atom.
- The nucleus is around 100,000 times smaller than the actual atom, and contains positively charged entities called protons, and neutral entities called neutrons
- The negatively charged particles, electrons, are present in a cloud around the nucleus.
- This model was also called the “planetary model of the atom” due to its analogy with the planetary system.
- According to Maxwell’s theory of electrodynamics, a charged particle under acceleration loses its energy. If this were to happen in Rutherford’s model, the electron would lose energy and hence its path would be am inward spiral: it would eventually collide with the nucleus. This however doesn’t actually happen.
- It could not explain the line spectra of hydrogen, or the discontinuous nature of its spectrum.