Q. A crystalline structure has radius ratio $(r_+ /r_-)$ in the range of $0.225 - 0.414$. The coordination number and arrangement of anions around the cations are
The Solid State
Solution:
Gustav F. Hüttig first proposed the radius ratio rule in 1920.
The table below gives the relation between radius ratio, coordination number and type of structure.
Radius Ratio
Coordination number
Type of structure
< 0.155
2
Linear
0.155 - 0.225
3
Triangular Planar
0.225 - 0.414
4
Tetrahedral
0.414 - 0.732
6
Octahedral
| Radius Ratio | Coordination number | Type of structure |
|---|---|---|
| < 0.155 | 2 | Linear |
| 0.155 - 0.225 | 3 | Triangular Planar |
| 0.225 - 0.414 | 4 | Tetrahedral |
| 0.414 - 0.732 | 6 | Octahedral |