In calcium fluoride, having the fluorite structure, the coordination numbers for calcium ion (Ca2+) and fluoride ion (F$$-$$) are
A
4 and 2
B
6 and 6
C
8 and 4
D
4 and 8
Explanation
In fluorite (CaF2) structure,
C.N. of Ca+2 = 8
C.N. of F–
= 4.
2
NEET 2016 Phase 1
MCQ (Single Correct Answer)
Lithium has a bcc structure. Its density is 530 kg m$$-$$3 and its atomic mass is 6.94 g mol$$-$$. Calculate the edge length of a unit cell of lithium metal. (NA = 6.02 $$ \times $$ 1023 mol$$-$$1)
A
527 pm
B
264 pm
C
154 pm
D
352 pm
Explanation
For bcc structure we have, Z = 2
Given, $$\rho $$ = 530 kg m–3
atomic mass of Li = 6.94 mol–1
NA= 6.02 × 1023 mol–1
$$\rho $$ = 530 kg m–3 = $${{530 \times 1000} \over {{{\left( {100} \right)}^3}}} = $$ 0.53 g cm–3
The ionic radii of A+ and B$$-$$ ions are 0.98 $$ \times $$ 10$$-$$10 m and 1.81 $$ \times $$ 10$$-$$10 m. The coordination number of each ion in AB is
It lies in the range of 0.414 to 0.732 hence
coordination number of each ion will be 6 as the
compound will have NaCl type structure i.e.,
octahedral arrangement.
4
AIPMT 2015 Cancelled Paper
MCQ (Single Correct Answer)
A given metal crystallises out with a cubic structure having edge length of 361 pm. If there are four metal atoms in one unit cell, what is the radius of one atom?