Looking for classes? Ksquare Career Institute, Bengaluru →
Voids in close packing
Concepts tested here
- Formula from occupied voids
- Octahedral voids
All Questions
2012 AIPMT-MAINS 1 question
-
Structure of a mixed oxide is cubic close-packed (c.c.p). The cubic unit cell of mixed oxide is composed of oxide ions. One fourth of the tetrahedral voids are occupied by divalent metal A and the octahedral voids are occupied by a monovalent metal B. The formula of the oxide is:$O^{2-}$ ions form the ccp lattice, so there are 4 oxide ions per unit cell.
Tetrahedral voids = 8; one fourth are occupied by $A^{2+}$: $\frac{1}{4}\times8 = 2$
Octahedral voids = 4; all are occupied by $B^+$: 4
Formula: $A_2B_4O_4$, i.e. $AB_2O_2$ (charge check: +2 + 2 − 4 = 0)
2012 AIPMT-PRE 1 question
-
The number of octahedral void(s) per atom present in a cubic close-packed structure isA ccp (fcc) unit cell has 4 atoms.
Octahedral voids: 1 at the body centre + 12 edge centres × $\frac{1}{4}$ = 4
Octahedral voids per atom $= \frac{4}{4} = 1$