Radius ratio Chemistry Notes

Radius ratio Chemistry Notes

The ratio between radii of cation and anion is called radius ratio.

  • Radius ratio = \(\frac{\text { Radius of Cation }}{\text { Radius of Anion }}\)
  • Radius ratio = \(\frac{r^{+}}{r^{-}}\)

→ We can get information about coordination number of cation or anion in ionic crystals with the help of radius ratio. So, the structure of ionic crystal lattice can also be determined by radius ratio. It is called radius ratio law. Different coordination number and radius ratio of structure of crystal lattice is given in following table 1.5.

Radius ratio Chemistry Notes

Limiting Radius Ratio and Crystalline Structure

Limiting | Radius Ratio 1 Coordination


Structure of | Crystal Example
0.155 – 0.225 3 Trigonal planar B2O3
0.225 – 0.414 4 Tetrahedral ZnS
0.414 – 0.732 6 Octahedral i NaCl, KCl
0.732 – 1.00 8 Cubic CsCl, RbCl

Chemistry Notes