History of Atomic Models – Nuclear Atom Who proposed, based on scattering experiments, that most of an atom’s mass is concentrated in a small, dense nucleus?

Introduction / Context:
Early twentieth-century experiments on alpha-particle scattering transformed our view of atomic structure. This question asks you to identify the scientist who concluded that atoms have a tiny, massive nucleus containing most of their mass.

Given Data / Assumptions:

• Gold-foil experiment with alpha particles.
• Large-angle scattering events inconsistent with a diffuse “plum pudding” model.
• We must name the proposer of the nuclear atom.

Concept / Approach:
Ernest Rutherford interpreted Geiger–Marsden results and proposed the nuclear model: a compact, positively charged nucleus with electrons orbiting (later refined by Bohr and quantum mechanics). Thomson (not “Thompson”) proposed the earlier plum-pudding model; Bohr introduced quantized orbits around Rutherford’s nucleus; Einstein’s work was not on atomic structure models of this type.

Step-by-Step Solution:

Verification / Alternative check:
The calculated nuclear radius (~10^-15 m) compared with atomic radius (~10^-10 m) explains why most alpha particles pass through, while a few scatter strongly—matching experimental statistics.

Why Other Options Are Wrong:

• Thompson (Thomson): Proposed the diffuse model contradicted by scattering results.
• Bohr: Built on Rutherford by quantizing electron orbits; not the discoverer of the nucleus.
• Einstein: Not associated with proposing the nuclear atom model.

Common Pitfalls:
Spelling confusion (Thomson vs. Thompson) and crediting Bohr with the nucleus discovery. Bohr refined energy levels; Rutherford identified the nucleus.

Final Answer:
Rutherford