Which order are correct? (I) Thermal stability : BeSO4 < MgSO4 < CaSO4 < SrSO4 < BaSO4 (II) Basic na — Chemical Bonding Chemistry Question

💡 Solution & Explanation

Step 1: Bond length is inversely proportional to bond order. We can determine the relative 'S-O' bond lengths by calculating the bond orders of each species using resonance structures. Step 2: Calculate the bond orders: In SO_3^2- (sulfite), there are 4 bonds shared among 3 regions, giving a Bond Order = 1.33. In SO_4^2- (sulfate), there are 6 bonds shared among 4 regions, giving a Bond Order = 1.5. In SO_2, there are 3 bonds shared among 2 regions, giving a Bond Order = 1.5. However, due to its neutral charge and lack of steric/electrostatic expansion, SO_2 has a slightly shorter S-O bond than SO_4^2-. In SO_3, there are 6 bonds shared among 3 regions, giving a Bond Order = 2.0. Step 3: Since bond length decreases as bond order increases, the correct decreasing order of 'S-O' bond length is SO_3^2- > SO_4^2- > SO_2 > SO_3. Thus, the correct option is (b).