Question

A solid `A^+ B^-` has NaCl type close packed structure. If the anion has a radius of 250 pm, what should be the ideal radius of the cation ? Can a cation `C^+` having a radius of 180 pm be slipped into the tetrahedral site of the crystal `A^+ B^-` ? Give reason for your answer.

Answer 1

Correct Answer - 103.4 pm. No
`(r_(+)(C^+))/(r_(-)(B^-))="180pm"/"250pm"=0.72`
It does not lie in the range 0.225-0.414 . Hence, `C^+` cannot be slipped into the tetrahedral site.