Radius rule and coordination number for ionic crystals:

1.	Radius rule and coordination number for ionic crystals:
Answer» In simple ionic crystals, the cations commonly occupy the voids or holes. The voids are empty spaces left between anionic spheres. i. Radius Ratio \(\left(\cfrac{r^+}{r^-}\right):\) The critical radius ratio of the void (cation) and sphere (anion), is calculated by solid geometry. \(\therefore\) Radius ratio = \(\cfrac{r^+}{r^-}\)\(=\cfrac{Cation\,radius}{Anion\,radius}\) ii. Coordination Number (CN) : The number of spheres (atoms, molecules or ions) directly surrounding a single sphere in a crystal, is called coordination number.

Answer»

In simple ionic crystals, the cations commonly occupy the voids or holes. The voids are empty spaces left between anionic spheres.

i. Radius Ratio \(\left(\cfrac{r^+}{r^-}\right):\)

The critical radius ratio of the void (cation) and sphere (anion), is calculated by solid geometry.

\(\therefore\) Radius ratio = \(\cfrac{r^+}{r^-}\)\(=\cfrac{Cation\,radius}{Anion\,radius}\)

ii. Coordination Number (CN) :

The number of spheres (atoms, molecules or ions) directly surrounding a single sphere in a crystal, is called coordination number.

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