Which of the following is not a conclusion of Rutherford's atomic model? — Atomic Structure Chemistry Question

💡 Solution & Explanation

### Step 1 - Rutherford's Alpha-Particle Scattering Experiment Conclusions In 1911, Rutherford bombarded thin gold foil with $\alpha$-particles ($\ce{He^{2+}}$) and drew these conclusions: 1. Most $\alpha$-particles passed straight through → most of atom is empty 2. Few deflected at large angles → positive charge and mass concentrated in a tiny nucleus 3. Nuclear dimensions are $\sim 10^{-15}\text{ m}$ vs atomic dimensions $\sim 10^{-10}\text{ m}$ → nucleus is very small compared to atom Rutherford proposed electrons revolve around the nucleus like planets, but gave **no restriction on which orbits** — no fixed energy levels. ### Step 2 - Bohr's Addition (1913) Niels Bohr introduced definite circular orbits of fixed energy to solve Rutherford's stability problem: $$mvr = \frac{nh}{2\pi}$$ This quantization of angular momentum was **Bohr's postulate**, not Rutherford's. ### Step 3 - Analysis of Options * **Option (A):** "Most of the part inside an atom is empty." — Direct conclusion from undeflected $\alpha$-particles. **Valid Rutherford conclusion.** * **Option (B):** "Almost all mass is concentrated in the nucleus." — Conclusion from large-angle scattering. **Valid Rutherford conclusion.** * **Option (C):** "Size of nucleus is very small compared to atom." — Quantitatively derived; ratio $\approx 10^5$. **Valid Rutherford conclusion.** * **Option (D):** "Electron revolves in definite orbits." — Rutherford only proposed circular paths; the concept of definite fixed-energy orbits was added by Bohr. **NOT a Rutherford conclusion.** $$\text{Correct Option: } \boxed{\text{D}}$$