Q. The limiting radius ratio for tetrahedral shape is:
ManipalManipal 2004The Solid State
Solution:
The limiting radius ratios (of cation and anion) play a very important role in giving a due to the nature of crystal structure of the ionic substance.
S.No.
Limiting radius ratio $(r+/r-)$
Shape
Co-ordination number
Example
1.
Less than $0.225$
Linear
2 or 3
$B_2O_3$
2.
$0.225 - 0.414$
Tetrahedral
4
$CuCl, CuBr, BaS, CuI$
3.
$0.414 - 0.732$
Square planer for 4 and octahedral for 8
4 or 6
$MgO, NaBr, MnO, KBr, AgCl, NaCl $
4.
$0.732$ more
Cube
8
$CsI, CsBr, NH_4Br $
| S.No. | Limiting radius ratio $(r+/r-)$ | Shape | Co-ordination number | Example |
|---|---|---|---|---|
| 1. | Less than $0.225$ | Linear | 2 or 3 | $B_2O_3$ |
| 2. | $0.225 - 0.414$ | Tetrahedral | 4 | $CuCl, CuBr, BaS, CuI$ |
| 3. | $0.414 - 0.732$ | Square planer for 4 and octahedral for 8 | 4 or 6 | $MgO, NaBr, MnO, KBr, AgCl, NaCl $ |
| 4. | $0.732$ more | Cube | 8 | $CsI, CsBr, NH_4Br $ |