In which of the following pairs first compound have more covalent nature than second compound?

(a) SnCl₂, SnCl₄

(b) PbCl₄, PbCl₂

(c) UF₆, UF₄

More the charge on cation more will be polarising power and more will be covalent character.

Correct Option: Only (b) and (c)

Explanation:

According to Fajans' Rules, the covalent character of an ionic bond depends on the polarising power of the cation and the polarisability of the anion. The polarising power of a cation increases with an increase in its positive charge (oxidation state) and a decrease in its ionic radius.

Therefore, higher charge on the cation ⇒ Greater polarising power ⇒ Greater distortion of electron cloud ⇒ More covalent character.

Let us analyze each pair to compare the covalent character of the first compound relative to the second compound:

Pair (a): SnCl₂ and SnCl₄

• Oxidation state of Sn in SnCl₂ is +2 (Sn²⁺).

• Oxidation state of Sn in SnCl₄ is +4 (Sn⁴⁺).

Since Sn⁴⁺ has a higher positive charge than Sn²⁺, SnCl₄ has a higher polarising power and thus a more covalent nature than SnCl₂.

Hence, the first compound (SnCl₂) has less covalent nature than the second compound (SnCl₄).

Pair (b): PbCl₄ and PbCl₂

• Oxidation state of Pb in PbCl₄ is +4 (Pb⁴⁺).

• Oxidation state of Pb in PbCl₂ is +2 (Pb²⁺).

Since Pb⁴⁺ has a higher charge than Pb²⁺, it has higher polarising power, making PbCl₄ more covalent than PbCl₂.

Hence, the first compound (PbCl₄) has more covalent nature than the second compound (PbCl₂).

Pair (c): UF₆ and UF₄

• Oxidation state of U in UF₆ is +6 (U⁶⁺).

• Oxidation state of U in UF₄ is +4 (U⁴⁺).

Since U⁶⁺ has a higher charge than U⁴⁺, it exerts a greater polarising effect on fluoride ions, making UF₆ more covalent than UF₄.

Hence, the first compound (UF₆) has more covalent nature than the second compound (UF₄).

Thus, the first compound is more covalent than the second compound in pairs (b) and (c).