Question

In CCP, there are 8 tetrahedral sites and all are present completely inside the unit cell. There are 13 octahedral sites out of which 1 is at the body centre and 12 are at edge centres. Like CCP, another packing is HCP, in which the number of tetrahedral sites that are completely inside one unit cell is x.

Find the value of x.

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Answer 1

*Question:—

In CCP, there are 8 tetrahedral sites and all are present completely inside the unit cell. There are 13 octahedral sites out of which 1 is at the body centre and 12 are at edge centres. Like CCP, another packing is HCP, in which the number of tetrahedral sites that are completely inside one unit cell is x.

• → Find the value of x.

*Answer:—

*The number of tetrahedral and octahedral voids in CCP unit cell is 8,4 respectively.

*The number of particles in ccp=4. Hence the number of tetrahedral and octahedral voids are 8 and 4 respectively.

Note:—

→ The number of tetrahedral voids is twice the number of particles.

→ The number of octahedral voids is equal to the number of particles.

Hence our correct answer is 8,4

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$@vikramjeeth$

Answer 2

CONCEPT: HCP (hexagonal closed packing) has layer sequence in ABABAB manner.

• CCP (cubic closed packing) has layer sequence in ABCABC manner.

GIVEN: Tetrahedral sites in CCP = 8

Octahedral sites = 13

Body centred = 1

Edge centred = 12

FIND: Tetrahedral sites (x) which are completely inside unit cell.

SOLUTION:

In HCP, total no. of tetrahedral sites = 12

Out of which 4 tetrahedral sites are present on the edge of unit cell.

therefore, no. of tetrahedral sites (x) that are completely inside one unit cell = 12 - 4

= 8

Hence number of tetrahedral sites that are completely inside one unit cell of HCP is 8.

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