Question

Which of the following compounds has maximum covalent character?

• A. \(\text{LiCl}\)
• B. \(\text{LiI}\)
• C. \(\text{NaCl}\)
• D. \(\text{NaI}\)

Hint:

To find maximum covalent character: Choose \textbf{small cation + large anion}. Order of anion size: \(\text{I}^->\text{Br}^->\text{Cl}^->\text{F}^-\)

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The covalent character in predominantly ionic compounds can be determined using Fajan's Rules. Covalent character increases with the polarization of the anion by the cation.
Step 2: Key Formula or Approach:
According to Fajan's Rules, maximum covalent character is favored by:
1. Smaller size of the cation.
2. Larger size of the anion.
3. Higher charge on the cation or anion.
Step 3: Detailed Explanation:
Let's compare the given alkali metal halides based on the sizes of their constituent ions:
- Cations: We have \(\text{Li}^+\) and \(\text{Na}^+\). Since lithium is above sodium in group 1, \(\text{Li}^+\) is smaller than \(\text{Na}^+\). A smaller cation has a higher polarizing power.
- Anions: We have \(\text{Cl}^-\) and \(\text{I}^-\). Since iodine is below chlorine in group 17, \(\text{I}^-\) is significantly larger than \(\text{Cl}^-\). A larger anion is more easily polarizable.
To maximize covalent character, we need the smallest cation combined with the largest anion. This combination is \(\text{Li}^+\) with \(\text{I}^-\), forming \(\text{LiI}\).
Step 4: Final Answer:
Therefore, \(\text{LiI}\) will exhibit the maximum covalent character among the given options.