Question

The number of spheres in contact with tetrahedral void is:
A. 3
B. 6
C. 4
D. 8

Answer 1

Hint: This question is asked from the topic of voids in the solid state chapter. We need to know the different types of voids present in a structure while the close packing occurs. Close packing can be done in 1D, 2D and 3D.

Complete step by step answer:
- We know that in the three dimensional structure, both in cubic close packing and hexagonal close packing in solids, about 26 % of total space is vacant. These vacant spaces are known as voids in crystals. There are two types of voids in three dimensional structure. That is tetrahedral voids and octahedral voids.
- In the cubic close packing, spheres of the second layer lie above the triangular voids of the first layer. All the spheres touch the three spheres of the first layer. By joining the centres of these four spheres, there forms a tetrahedron and the vacant space left over there forms a tetrahedral void. The figure of the tetrahedral void is as follows:

Therefore, the number of spheres in contact with tetrahedral void will be 4
So the correct answer is “C”:

Note: In the octahedral voids, three spheres of the first layer exactly placed on the three spheres in the second layer. So, the space left between these six spheres is the octahedral void. In the octahedral void, the number spheres in contact with the void is 6.