Question

what should be the ideal radius of the anion in a Nacl type of structure if the radius of the cation is r ​

Answer 1

In Na +CI crystal each Na + ion is surrounded by 6 CI + ions and vice versa. Thus Na + ion is placed in octahedral hole.

The limiting radius ratio for octahedral site = 0.414 or B −A += Rr =0.414

Given that radius of anion (B − )R=250 pm

i.e. radius of cation (A + )r=0.414R=0.414×250 pm

or r=103.5 pm

Thus ideal radius for cation (A + ) is r=103.5 pm.

We know that (r/R) for tetrahedral hole is 0.225.

∴ Rr =0.225

or r=0.225 R=0.225×250=56.25pm

Thus ideal radius for cation is 56.25 pm for tetrahedral hole. But the radius of C +

is 180 pm. It is much larger

then ideal radius i.e. 56.25 pm. Therefore we can not slipped cation C + into the tetrahedral site.

Answered By=shreyash. ..

MY DEAR FRIEND PLEASE THANKS MY 15 ANSWERS ☺☺