When β-particles are sent through a tin metal foil, most of them go straight through the foil as — Atomic Structure Chemistry Question

💡 Solution & Explanation

### Step 1 - Nature of $\beta$-Particles A **$\beta$-particle** ($\beta^-$) is a high-speed electron emitted during nuclear decay processes. * Charge: $q = -e \approx -1.602 \times 10^{-19}\text{ C}$ * Mass: $m_e \approx 9.109 \times 10^{-31}\text{ kg}$ --- ### Step 2 - Understanding the Atomic Structure According to the nuclear model of the atom, an atom consists of: 1. A centrally located, extremely dense, positively charged **nucleus** (radius $\sim 10^{-15}\text{ m}$). 2. An outer region where electrons orbit (radius $\sim 10^{-10}\text{ m}$). Volume ratio: $$\frac{V_{\text{atom}}}{V_{\text{nucleus}}} \approx \frac{(10^{-10})^3}{(10^{-15})^3} = 10^{15}$$ This demonstrates that **more than $99.99999999999\%$ of an atom's volume is empty space**. --- ### Step 3 - Interaction of $\beta$-Particles with Tin Foil When a beam of high-speed $\beta$-particles is directed at a thin tin metal foil, the vast majority pass through straight and undeflected because they travel through the empty space between the tiny nuclei. --- ### Step 4 - Systematic Analysis of the Options * **Option (A) $\beta$-particles are much heavier than electron:** Incorrect. A $\beta$-particle is a high-speed electron — its mass is exactly identical to that of an electron. * **Option (B) most part of the atom is empty space:** Correct. The straight-line trajectory of the majority of the $\beta$-particles is a direct physical consequence of the vast amount of empty space inside atoms. * **Option (C) $\beta$-particles are positively charged:** Incorrect. $\beta$-particles are negatively charged electrons ($-1e$). * **Option (D) $\beta$-particles move with high velocity:** Incorrect. Although $\beta$-particles do move with high velocities, speed alone does not explain why they pass straight through. Even very fast particles would scatter or be absorbed if the atom were a solid sphere. $$\text{Correct Option: } \boxed{\text{B}}$$