Question

Rutherford's alpha-particle scattering experiment was responsible for the discovery of:
A) Atomic nucleus
B) Electron
C) Proton
D) Neutron

Answer 1

Ernest Rutherford performed a scattering of alpha particles experiment. He bombarded the positively charged alpha particles on the layered gold foil. He expected that the alpha particles would be reverted back in the same path as bombarded on the foil. However, the observed results were different. Such that, most of the alpha particles passed through the foil, only a few particles experience the deflection by small angles.

Complete step by step answer:
Ernest Rutherford wanted to know about the electrons which are arranged in the atoms. In the Rutherford experiment, the fast-moving alpha particles were allowed to fall on the gold foil.
The gold foil was bombarded with the alpha particles. This gold foil was about 1000 atoms thick. The alpha particles are doubly charged helium ions and they have a mass of 4 units. This is fast-moving particles that interact with the particles of the gold atoms.
Rutherford expected that the alpha particles would be reverted by the subatomic particles in the gold. The alpha particles are heavier than the proton, it was expected that the alpha particles would be reverted back in the same path. However, the observed results were different than expected.
The observations of the Rutherford experiments are as follows:

1. The fast-moving alpha particles were observed to be passed straight through the foil without any interaction with the foil.
2. Some alpha particles experience the deflection by small angles.
3. and most surprisingly only a single alpha particle out of the 12,000 alpha particles appeared to be reverted by the $\text{ 18}{{\text{0}}^{\text{0}}}$ .
   Thus, he has drawn the following conclusions:
4. He concluded that the atom is the spacious mass. The alpha particles passed without any interacting or without getting deflected, which means that most of the spaces in the atom are vacant.
5. Few of the alpha particles experience the deflection, this emphasizes that the cause for the deflection is occupying very little space of the atom. Since, the $\text{ }\alpha \text{ }$ particles experience the deflection means that the charge on the mass must be positive.
6. Only one $\text{ }\alpha \text{ }$particle experiences the deflection by the larger angles, suggesting that the positive charge and the mass of the atom are situated in the very small volume of the atoms.
   From this Rutherford put forward a model of the atom, which has a positive charge at the centre of mass and he named it a ‘nucleus’. The entire mass of the atom lies at the nucleus. The electrons which are negatively charged revolve around the positively charged nucleus in orbits.
   Rutherford's $\text{ }\alpha \text{ }$-particle scattering experiment was responsible for the discovery of the atomic nucleus.

Hence, (A) is the correct option.

Note: Rutherford assumed that the only force which exists between the alpha particles and the atoms of the foil is the coulombic force of repulsion since the nucleus and alpha particles are positively charged and repel each other. His primary assumption was that the positive charge is everywhere in the atom, however, the scattering experiment contradicts the statement.