Question

ABCABC... type of arrangement of different layers in a closed packed structure is called as:

Answer 1

Hint: We know that the lattice is an ordered array of points describing the arrangement of particles that form a crystal. The unit cell of a crystal is defined by the lattice points. The unit cell is the smallest part of a crystal that repeated regularly through translation in three dimensions creates the whole crystal.

Complete answer:
The cubic close packing (CCP) arrangement is obtained when the third layer of a structure is placed over the second layer. Now, when the third layer is placed over the second, there are only two possibilities. First possibility by covering tetrahedral voids and the second by covering octahedral voids. First, we will understand tetrahedral voids and octahedral voids. So tetrahedral voids are formed when the sphere of the second layer is above the void of the first layer. Octahedral voids are present at the edge Centre and body Centre When the third layer is placed over the second by covering tetrahedral voids then in this possibility the sphere of the third layer will be symmetric with the first layer and if we follow the pattern the spheres of the second layer will be aligned with the fourth layer and so on. The different packing structures or types can be identified on the basis of the molecular arrangement in a given lattice. Each type of packing structure has a unique arrangement of atoms within them that can be understood by viewing the lattice from a side profile.
So, now we can conclude that the pattern of spheres is repeated in alternate layers. The pattern can be written as ABAB; this pattern is called hexagonal packed structure (HCP).

Now, when the third layer is placed over the second layer such that it covers the octahedral voids. In this manner, the third layer is not aligned with either of the first or second. So if we consider the first layer as A, the second layer as B. and the third layer formed as C and so on. The pattern designated will be ABCABC.... The pattern of successive layers of CCP arrangement can be designated as ABCABC….
Therefore, ABCABC... type of arrangement of different layers in a closed packed structure is called cubic closest packed (CCP).

Note:
There is a very important point to remember in the ABC ABC ABC ….... pattern and that is if spheres of the third layer are placed into tetrahedral voids, the packing is hcp (hexagonal close packing). CCP is cubic close packing; it is also called FCC (face-centered cubic). In FCC (face-centered cubic), spheres of the third layer are placed into octahedral voids. -The number of these two types of voids depends upon the number of close-packed spheres.