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Difficulty: MediumAtomic Models

In Rutherford's α\alpha-particle scattering experiment, most of the α\alpha-particles passed straight through the gold foil with negligible deflection, while a very small fraction was scattered through angles greater than 90∘90^\circ. Which fundamental deduction about atomic structure was directly established by these rare, large-angle scatterings?

  1. The positive charge and nearly all the atomic mass are concentrated in an extremely small, dense central region called the nucleus.Answer
  2. B
    Electrons revolve around the positive center in discrete, non-radiating stationary orbits.
  3. C
    The positive charge is distributed uniformly throughout a sphere of atomic dimensions containing embedded electrons.
  4. D
    Orbiting electrons continuously radiate energy, causing them to gradually spiral inward toward the center.

Answer

The positive charge and nearly all the atomic mass are concentrated in an extremely small, dense central region called the nucleus.
Large-angle deflection (>90∘>90^\circ) requires an immense repulsive Coulomb force, which can only occur if the entire positive charge and virtually all atomic mass are concentrated in a tiny central region (the nucleus). If positive charge were spread out over the entire atomic volume, the maximum electric field would be far too weak to turn back high-velocity alpha particles.

Step-by-Step Solution

1
Analyze the experimental observations from Rutherford's alpha-scattering experiment.
Most α\alpha-particles pass undeflected (indicating mostly empty space), while a tiny fraction scatter at angles >90∘>90^\circ.
Understanding the physical cause of large-angle electrostatic deflection.
2
Relate electrostatic repulsive force to mass and charge distribution.
To turn around a fast-moving positive α\alpha-particle (He2+He^{2+}), it must experience a intense Coulomb repulsion F=14πε0q1q2r2F = \frac{1}{4\pi\varepsilon_0}\frac{q_1 q_2}{r^2} at very small distance rr.
A diffuse charge distribution (Thomson model) yields weak electric fields that cannot cause wide-angle scattering.
3
Identify the structural conclusion drawn by Rutherford.
The entire positive charge and mass must reside in a massive, concentrated center (the nucleus).
Directly matches the core physical takeaway of the nuclear atomic model.

Key Concept

Rutherford Nuclear Model and Alpha Scattering Deduction
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Topics

Atomic Models

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