Question

The number of tetrahedral voids present on each body diagonal in CCP unit cell is:
A) 1
B) 2
C) 3
D) 4

Answer 1

Hint: The concept of the crystallography in physical and also inorganic chemistry part which includes the description of crystal lattices gives the answer. Here, voids are nothing but the empty spaces present in CCP unit cells.

Complete step by step answer:
We have studied about the topic named crystallography in our lower classes and also about various types of crystal lattices according to Bravais lattice and about the calculation of atomic radius too.
We shall now see the meaning of voids and also what CPP is.
- Tetrahedral voids is the one where a void is surrounded by four spheres placed at the corners of a regular tetrahedron and whenever the sphere of the second layer is above the void of the first layer then the tetrahedral void will be formed.
- CCP or cubic close packed unit cell is the well known densest possible packing of equal spheres and in this cubic close packing there are arranging layers of close packed spheres such that the spheres of every third layer overlay one another.
- In CCP the number of atoms present per unit cell is 4 and since in cubic packing, the tetrahedral voids are equal to twice the number of atoms present per unit cell and therefore, total tetrahedral voids will be $2\times 4=8$
Since, these voids are uniformly distributed over each of the four body diagonals the number of tetrahedral voids present on each body diagonal will be $\frac{8}{4}=2$

Therefore, the correct answer is option B) 2.

Note: The void is much smaller than the sphere and has a small volume. Void is an empty space where the coordination number of a tetrahedral void is four and this is because the void forms at the centre of the four spheres.