Question

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R.
Assertion A : Lithium halides are some what covalent in nature.
Reason R : Lithium possess high polarisation capability.
In the light of the above statements, choose the most appropriate answer from the options given below :

• A. Both A and R are true and R is the correct explanation of A.
• B. Both A and R are true but R is NOT the correct explanation of A.
• C. A is true but R is false.
• D. A is false but R is true.

Hint:

Fajan's rules are key to understanding the covalent character in ionic bonds. High covalent character is favored by: 1) Small, highly charged cation (high polarizing power) and 2) Large, highly charged anion (high polarizability). Li$^+$ is a classic example of a cation with high polarizing power.

Answer 1

The Correct Option is A

Assertion A states that lithium halides are somewhat covalent in nature. This is a true statement. According to Fajan's rules, although formed between a metal and a non-metal, lithium halides (especially LiI) exhibit significant covalent character. For instance, LiCl is soluble in organic solvents like ethanol.
Reason R states that lithium possesses high polarisation capability. This is also a true statement. The term "polarisation capability" refers to the polarizing power of the cation. The Li$^+$ ion is very small and has a relatively high charge density. This allows it to distort the electron cloud of the larger halide anion to a significant extent.
Connecting the Assertion and Reason: The high polarizing power (polarisation capability) of the Li$^+$ ion is precisely the reason why it can pull the electron density from the anion, leading to a sharing of electrons and thus covalent character in the bond. Therefore, Reason R is the correct explanation for Assertion A.