Question

a crystalline solid ab has NaCl type structure with radiud of B- ion is 250pm. Which of the following cations can be made to slip into tetrahedral site of crystals of a+b_

Answer 1

Answer:

100<ra<175 pm

Explanation:nacl structure --》coordination no. Is 6--》rc/ra=0.414-0.732

0.414rb<ra<0.732rb

100<ra<175 pm

Answer 2

NANBA..

NaCl lattice is a simple cubic unit or FCC unit lattice.

Here B is the negative atom, generally containing the bigger radius and thus positive charged atom A has lower radius.

In case of tetrahedral voids,

a=√2R

or, R=√2a/2....(i)

where, a is one side of the lattice structure and R is the radius of the lattice point.

Here, R=250 pm

Now if 'r' be the radius of the void, for a diagonal of a cube,

2(R+r) = √3a.....(ii)

dividing equation (ii) by (i);

2(R+r)/R = √3a x 2 / √2a

or, 1 + r/R = √3/√2

or, r/R = 0.225

For tetrahedral void, r = 0.225 x 250 pm = 56.25 pm

The value of the radius of the atom to be fitted inside the void must be lesser than(or equal) 56.25 pm

Hope usefull...

drrang all the best for ur NEET exams