The Coordination Number of bcc, fcc, ccp, hcp is

Answer:

Closest Packed Hexagonal (HCP)

The third level of a hexagonal closest packed structure will have the same spherical configuration as the first layer and fills all of the tetrahedral holes. The stacking of hcp may be expressed as “a-b-a-b-a-b,” because the structure replicates itself every two levels. In a hexagonal tightest packed configuration, the atoms effectively occupy 74% of the space, leaving 26% unoccupied.

Closest Packed Cubic (CCP)

In a cubic closest packing, the arrangement efficiently takes up 74 percent of the space. The second layer of spheres is put on half of the depressions of the previous layer, similar to hexagonal closest packing.

The third layer differs from the preceding two layers in that it is placed in the depressions of the second layer, thereby filling all of the octahedral holes.

The third layer’s spheres do not line up with those in layer A, and the structure does not recur until a fourth layer is added. So because the fourth layer is identical to the previous, the layers are arranged “a-b-c-a-b-c.”

Coordination number:

• The hexagonal closest packed (hcp) contains 6 atoms and also has a coordination number = 12
• This face-centred cubic (fcc) does have a coordination number = 12 as well as a unit cell size of 4 atoms
• This body-centred cubic (bcc) does have a coordinate coordination number = 8 and 2 atoms per unit cell
•  A simple cubic does have a coordination number = 6 so each unit cell holds 1 atom