Which of the following is a covalent compound? — Chemical Bonding Chemistry Question

💡 Solution & Explanation

Step 1: Apply Fajan's rules to evaluate the ionic versus covalent character of the aluminum compounds. Covalent character is maximized when there is a small, highly charged cation and a large, highly polarizable anion. Step 2: Comparing the anions (O^2-, F^-, Cl^-, and SO4^2-), the chloride ion (Cl^-) is larger and has a much higher polarizability than the small fluoride (F^-) and oxide (O^2-) ions. This allows the Al^3+ cation to heavily polarize the electron cloud of the chloride ions. Step 3: This high polarization results in AlCl3 having a highly covalent molecular nature (forming Al2Cl6 dimers in gas/non-polar phases) compared to the predominantly ionic lattices of AlF3 and Al2O3. Therefore, AlCl3 is the covalent compound, corresponding to option (c).