Question 1.7) How will you distinguish between the following pairs of terms

 

Question 1.7) How will you distinguish between the following pairs of terms:

(i) Hexagonal close-packing and cubic close-packing?

(ii) Crystal lattice and unit cell?

(iii) Tetrahedral void and octahedral void?

Answer :

(a) Cubic close packing:-

When a third layer is placed over the second layer in a manner that the octahedral voids are covered by the spheres, a layer different from the first

(A) and second

(B) is obtained.

If we continue packing in this manner we get the cubic close packing.Hexagonal close packing: When the third layer is placed over the second layer in a way that the tetrahedral voids are covered by the spheres, a 3D close packing is produced where spheres in each third or alternate layers are vertically aligned. If we continue packing in this order we get hexagonal close packing.

(b) Unit cell:-

It is the smallest 3D dimensional portion of a complete space lattice, which when repeated over and over again in different directions from the crystal lattice.

Crystal lattice :-

it is a regular orientation of particles of a crystal in a 3D space.

(c) Octahedral void :-

it is a void surrounded by 6 spheres.

Tetrahedral void :-

it is a void surrounded by 4 spheres.