Question

Distinguish between hexagonal close packing and cubic close packing.

In what way is the hexagonal close packing different from cubic close-packing?

How will you distinguish between the following pair of terms?

Hexagonal close-packing and cubic close-packing

Answer 1

Sr. No.	Hexagonal close packing	Cubic close packing
1.	In hcp, the unit cell is a hexagonal prism with a repeating ABABABA... stacking pattern.	In ccp, the unit cell is a face-centred cubic (fcc) structure with a repeating ABCABCA... stacking pattern.
2.	In this case, the spheres of the third layer are exactly aligned with those of the first layer.	In this case, the spheres of the third layer are not aligned with those of the first layer or second layer; only when the fourth layer is placed are its spheres aligned with the first layer.
3.	In hcp, tetrahedral voids of the second layer may be covered by the spheres of the third layer.	In ccp, the third layer may be placed above the second layer in a manner such that its sphere covers the octahedral voids.

Answer 2

Property	Hexagonal Close Packing (hcp)	Cubic Close Packing (ccp)
Unit Cell Structure	In hcp, the unit cell is a hexagonal prism with a repeating ABAB stacking pattern.	In ccp, the unit cell is a face-centred cubic (fcc) structure with a repeating ABCABC stacking pattern.
Coordination Number	In hcp, each atom is surrounded by 12 nearest neighbours, resulting in a coordination number of 12.	In ccp, each atom is also surrounded by 12 nearest neighbours, resulting in a coordination number of 12.
Number of Atoms per Unit Cell	An hcp unit cell contains 6 atoms.	A ccp unit cell contains 4 atoms.
Symmetry	Hcp has a lower symmetry compared to ccp and forms a more compact structure.	Ccp has higher symmetry and forms a more regular, cubic structure.
Examples	Elements like Magnesium (Mg), Zinc (Zn), and Titanium (Ti) crystallise in the hcp structure.	Elements like Copper (Cu), Silver (Ag), and Gold (Au) crystallise in the ccp structure.