Question

In which of the following compounds are correctly arranged in the increasing order of their covalent character?

• A. \(\mathrm{SiCl_4<AlCl_3<NaCl<MgCl_2}\)
• B. \(\mathrm{NaCl<MgCl_2<AlCl_3<SiCl_4}\)
• C. \(\mathrm{NaCl<MgCl_2<SiCl_4<AlCl_3}\)
• D. \(\mathrm{SiCl_4<AlCl_3<MgCl_2<NaCl}\)

Hint:

According to Fajan's rule, \[ \boxed{\text{Higher charge and smaller cation} \Rightarrow \text{greater covalent character}.} \] Thus, \[ \boxed{\mathrm{NaCl<MgCl_2<AlCl_3<SiCl_4}.} \]

Answer 1

The Correct Option is B

Step 1: Apply Fajan's rule. Covalent character increases with increasing polarizing power of the cation. \[ \mathrm{Na^+<Mg^{2+}<Al^{3+}} \] Hence, \[ \mathrm{NaCl<MgCl_2<AlCl_3}. \]

Step 2: Compare with silicon tetrachloride. \[ \mathrm{SiCl_4} \] is a covalent molecular compound and has the highest covalent character. Therefore, \[ \boxed{\mathrm{NaCl<MgCl_2<AlCl_3<SiCl_4}} \] Hence, \[ \boxed{(B)} \] is the correct answer.