Oxygen is more electronegative than sulphur, yet is acidic in nature while is neutral because: — p Block Elements Chemistry Question

💡 Solution & Explanation

# Why $H_2S$ is Acidic While $H_2O$ is Neutral **Step 1: Identify the relevant factors** Acidity depends on two competing effects: - **Electronegativity of central atom**: Higher electronegativity → stronger H-X bond → less acidic - **Bond strength (H-X bond length)**: Longer, weaker bonds → easier to break → more acidic **Step 2: Compare H-O vs H-S bonds** | Bond | Length | Strength | |------|--------|----------| | H-O | 96 pm | Very strong | | H-S | 134 pm | Weaker | The H-S bond is significantly longer and weaker than H-O. **Step 3: Explain the acidity trend** $$H_2S \rightarrow H^+ + HS^- \quad (K_a \approx 10^{-7})$$ $$H_2O \rightarrow H^+ + OH^- \quad (K_w = 10^{-14})$$ Even though O is more electronegative, the **H-S bond is much longer and weaker**, making it easier to ionize. The $S^-$ ion, being larger, can better stabilize the negative charge compared to the smaller $O^-$. **Step 4: Conclusion** **Electronegativity favors lower acidity, but bond length/strength dominates.** Since the H-S bond breaks more easily, $H_2S$ is acidic despite S being less electronegative. This illustrates that **bond strength is the determining factor** in binary hydride acidity. **(Assuming Option C states: "The H-S bond is weaker/longer than H-O bond" or similar)**