Question

Which is the correct decreasing order for ionic character of halides, where M is a monovalent metal?

• A. \(\text{MF}>\text{MCl}>\text{MBr}>\text{MI}\)
• B. \(\text{MI}>\text{MBr}>\text{MCl}>\text{MF}\)
• C. \(\text{MI}>\text{MCl}>\text{MBr}>\text{MF}\)
• D. \(\text{MF}>\text{MBr}>\text{MCl}>\text{MI}\)

Hint:

Use Fajans' rules: a larger, more polarisable anion gives more covalent character and less ionic character.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept
According to Fajans' rules, covalent character increases with the polarisability of the anion, for the same cation.

Step 2: Compare the halide ions
The size of halide ions increases as \(\text{F}^{-}<\text{Cl}^{-}<\text{Br}^{-}<\text{I}^{-}\), so polarisability increases in the same order.

Step 3: Convert to ionic character
The most polarisable ion, \(\text{I}^{-}\), gives the most covalent compound, and \(\text{F}^{-}\) the most ionic.

Step 4: Compare the options
The decreasing order of ionic character is \(\text{MF}>\text{MCl}>\text{MBr}>\text{MI}\), option (A).

Final Answer:
Ionic character decreases from MF to MI. \[ \boxed{\text{(A) }\text{MF}>\text{MCl}>\text{MBr}>\text{MI}} \]