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A solid A^(+)B^(-) has NaCl-type close-p...

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 for the cation? Can a cation `C^(+)` having radius of `180` pm be slipped into the tetrahedral site of the crystal `A^(+)B^(-)`? Give reason for your answer.

Text Solution

Verified by Experts

The correct Answer is:
`No`
Limiting raidus ratio `(r_(o+))/(r_(ɵ)) = 0.414`
`r_(o+) = 0.414r_(ɵ)`
ideal radius for the cation `= 0.225(r_ɵ)`
`= 0.225 xx 250 = 56.25` pm
Since the size of the cation (`180` pm) is much larger than the ideal raidus (`56.25` pm), the cation introduced in `TV` of the crystal, pushes the anions outwards and the anions do not remain close packed. The new structure will be unstable.
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