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 competing factors** Acidity of a hydride depends on two factors: - **Electronegativity of the central atom** (favors $H_2O$ since O is more electronegative) - **Bond strength** (H-X bond dissociation energy) **Step 2: Analyze bond strength** The H-S bond is significantly weaker than the H-O bond: - H-S bond: ~366 kJ/mol - H-O bond: ~467 kJ/mol This is because S is larger than O, leading to poorer orbital overlap and a weaker bond. **Step 3: Apply the acidity principle** For a hydride $HX$ to ionize: $HX \rightarrow H^+ + X^-$ A weak bond is **easier to break**, facilitating proton release. Although O is more electronegative (which would stabilize $OH^-$), the much stronger H-O bond makes ionization prohibitively difficult. **Step 4: Conclusion** In $H_2S$, the weaker H-S bond can be broken more readily, allowing it to donate a proton and act as a **weak acid** in water. In $H_2O$, despite O's high electronegativity, the very strong H-O bond prevents significant ionization, making it **neutral** (only extremely weak autoionization occurs). **Answer C is correct because:** *Bond strength (size/orbital overlap of S vs O) outweighs electronegativity difference in determining hydride acidity.*