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The CsCl type structure is exhibited by...

The CsCl type structure is exhibited by alkali halides only when the radius of the cation is large enough to keep touching its eight nearst neighbour aniion. Below what minimum raiton of cation of anion radii `(r^(+)//r^(-))` this contact is prevented

A

0.225

B

0.414

C

0.632

D

0.732

Text Solution

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The correct Answer is:
To solve the problem, we need to determine the minimum radius ratio of cation to anion (r⁺/r⁻) below which the cation does not touch its nearest neighbor anions in a CsCl-type structure. ### Step-by-Step Solution: 1. **Understanding the CsCl Structure**: - CsCl (Cesium Chloride) has a cubic structure where each cation (Cs⁺) is surrounded by eight anions (Cl⁻) located at the corners of a cube. The cation and anion touch each other in this arrangement. 2. **Radius Ratio Concept**: - The radius ratio (r⁺/r⁻) is the ratio of the radius of the cation (r⁺) to the radius of the anion (r⁻). This ratio helps in predicting the type of structure formed by ionic compounds. 3. **Radius Ratio Rules**: - According to the radius ratio rules: - If 0.225 < r⁺/r⁻ < 0.414, the cation occupies tetrahedral holes. - If 0.414 < r⁺/r⁻ < 0.732, the cation occupies octahedral holes. - If r⁺/r⁻ > 0.732, the structure is cubic, and the cation and anion are in contact. 4. **Finding the Minimum Ratio**: - The question asks for the minimum radius ratio below which contact between the cation and anion is prevented. - From the radius ratio rules, we see that for the cation to just touch the anions, the ratio must be at least 0.732. Therefore, below this ratio, the cation will not be in contact with the anions. 5. **Conclusion**: - The minimum radius ratio (r⁺/r⁻) below which the contact between the cation and anion is prevented is **0.732**. ### Final Answer: The minimum radius ratio of cation to anion (r⁺/r⁻) below which contact is prevented is **0.732**.
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