Rutherford's alpha-particle experiment and its discovery:
Introduction:
Rutherford's alpha-particle experiment, also known as the gold foil experiment, was conducted by Ernest Rutherford in 1911. This experiment played a crucial role in understanding the structure of the atom and led to the discovery of the nucleus.
Experimental setup:
1. Rutherford directed a beam of α (alpha) particles towards a thin gold foil.
2. The α particles were obtained from a radioactive source, which emitted positively charged particles.
3. The gold foil was chosen due to its high malleability and the ability to be made into extremely thin layers.
Expected Observations:
Based on the prevailing model of the atom, called the Thomson's plum pudding model, Rutherford expected that the α particles would pass through the foil with slight deflections.
Actual Observations:
1. Most of the α particles passed through the gold foil without any deflection, just as expected.
2. However, a small fraction of the α particles experienced large-angle deflections and even bounced back in the direction from which they came.
Interpretation of results:
1. Based on the unexpected observations, Rutherford proposed a new model of the atom.
2. He concluded that atoms have a tiny, dense, and positively charged core at the center, which he called the nucleus.
3. The nucleus occupies a very small volume compared to the overall size of the atom.
4. The rest of the atom is mostly empty space, with negatively charged electrons revolving around the nucleus in specific energy levels.
Discovery resulting from the experiment:
The key discovery resulting from Rutherford's alpha-particle experiment was the existence of the nucleus.
Answer:
The correct answer is C: Nucleus.
In summary, Rutherford's alpha-particle experiment led to the discovery of the nucleus as the central, dense, and positively charged core of an atom. This experiment revolutionized our understanding of atomic structure and laid the foundation for the development of the modern atomic model.

Rutherford’s Alpha-Particle Experiment
Rutherford's alpha-particle experiment, conducted in 1909, was pivotal in our understanding of atomic structure. This groundbreaking experiment involved firing alpha particles at a thin gold foil and observing their scattering patterns.
Key Findings of the Experiment
- Deflection of Alpha Particles: Most alpha particles passed straight through the foil, while a small fraction were deflected at large angles.
- Conclusion on Atomic Structure: The significant deflection indicated that a concentrated mass exists within the atom, leading to the conclusion that atoms consist mostly of empty space with a dense core.
Discovery of the Nucleus
- Identification of the Nucleus: Rutherford proposed that the dense core is the nucleus, which contains positively charged particles (protons) and is responsible for the atom's mass.
- Revolutionary Shift: This was a major shift from the earlier plum pudding model by J.J. Thomson, which depicted atoms as a diffuse cloud of positive charge with electrons embedded.
Significance of the Discovery
- Foundation of Modern Atomic Theory: The identification of the nucleus laid the groundwork for the modern understanding of atomic structure, influencing future research in physics and chemistry.
- Impact on Science: Rutherford's discovery led to further exploration of subatomic particles, ultimately resulting in the discovery of neutrons and a more comprehensive understanding of atomic interactions.
In summary, Rutherford's alpha-particle experiment was crucial in establishing the existence of the nucleus, fundamentally changing the way scientists understood the structure of atoms.