Question

The pattern in Hexagonal close packing and cubic close packing are the same. Is this statement true or false?
(A) True
(B) False

Answer 1

Hint: In Hexagonal close packing, the third layer of atoms is arranged in a way that it covers the tetrahedral voids. While in CCP, the third layer of atoms covers the octahedral voids.

Complete step by step solution:
We will need to understand how the particles are arranged in both types of close packing arrangements in order to compare them.

- In Hexagonal close-packing structure, we can see two layers of atoms are arranged simultaneously over each other in order to make the final three-dimensional close packing structures. We can see in the figure that the first layer of HCP contains a hexagonal arrangement in a two-dimensional view. Now, the second layer of the atom is the same in both Hexagonal close packing and cubic close packing structure.
- The difference in arrangement comes in the way the third layer is arranged. In Hexagonal close packing, the third layer is the same as the first layer and if we name the first layer as A and the second layer B, then we can say that its three-dimensional structure will be in the pattern of ABABAB…. Here, the tetrahedral voids of the second layer are covered by the third layer.
- Hexagonal close-packing structure is found in many metals like Magnesium and zinc.
- In cubic close packing, the third layer is arranged in a way that its spheres cover the octahedral voids. This arrangement is different from the first and second layer. So, we can call the third layer of the C layer. Thus, we can say that in cubic close packing the pattern of the structure is like ABCABCABC….
- Metals like copper and silver are arranged in CCP close packing.

Thus, we can conclude that this statement is the false and the correct answer is (B).

Note: Remember that both CCP (cubic close-packed) and FCC (face-centred cubic) structures are the same. They both have the same arrangement of atoms. The empty space between the four spheres joined together is called tetrahedral voids. The voids that are surrounded by six spheres are called octahedral voids.