Question

If the Thompson model of the atom was correct, then the result of Rutherford's gold foil experiment would have been :

• A. All of the $\alpha$-particles pass through the gold foil without decrease in speed.
• B. $\alpha$-Particles pass through the gold foil deflected by small angles and with reduced speed.
• C. $\alpha$-Particles are deflected over a wide range of angles.
• D. All $\alpha$-particles get bounced back by 180$^\circ$.

Hint:

Rutherford's gold foil experiment was a pivotal moment in atomic theory. The key observation was the large-angle scattering of a few alpha particles, which was completely unexpected based on Thomson's model and implied a small, dense, positively charged nucleus.

Answer 1

The Correct Option is A

The question pertains to Rutherford's gold foil experiment and its implications on the Thompson model of the atom.

Background: The Thompson model, also known as the "plum pudding model," proposed that an atom is a sphere of positive charge with electrons embedded within it. According to this model, the positive charge is spread out over a large volume, and thus there is no significant concentration of charge to deflect charged particles significantly.

Rutherford's Gold Foil Experiment: Rutherford directed a beam of $\alpha$-particles (positively charged helium nuclei) at a thin sheet of gold foil. According to the experiment's findings:

1. Most of the $\alpha$-particles passed through the foil with little or no deflection.
2. A small fraction of the particles were deflected through large angles.
3. An even smaller fraction were reflected back towards the source.

Implication for the Thompson Model:

If the Thompson model were correct, the positive charge is not concentrated enough to cause significant deflection. Therefore, the expected result would have been that all the $\alpha$-particles would pass through the gold foil without a decrease in speed or significant deflection, as the positive charge would be too diffuse to influence the trajectory of the $\alpha$-particles significantly.

Thus, the correct answer is: All of the $\alpha$-particles pass through the gold foil without decrease in speed.

This was a significant experimental contradiction that led to the conclusion that the positive charge, and most of the mass of the atom, must be concentrated in a very small, dense region known as the nucleus, leading to the development of the Rutherford model of the atom.