Question

The ABAB.. type packing and ABCABC.. type packing are respectively called as:

• A. hexagonal close packing (hcp) and cubic close packing (ccp)
• B. cubic colsed packing (ccp) and hexagonal colsed pacing (hcp)
• C. body centered cubic(bcc) close packing and hexagonal close packing (hcp)
• D. hexgonal closed packing (hcp) and body centred cubic (bcc) close packing

Answer 1

The correct option is A hexagonal close packing (hcp) and cubic close packing (ccp)

There are two types of 3-D closed packing is possible from 2-D close packing:
1.) Cubic close packing (ccp)
2.) Hexagonal close packing (hcp)

In ccp, the second row of spheres is placed in the interstices or depressions of the first-row spheres. The third layer is placed over the second layer covering the octahedral voids of the second layer so that the spheres of the third layer are not aligned with neither the first nor the second layer. Thus, it gives ABCABC... type of arrangement. This structure is called cubic close packed (ccp) or face-centred cubic (fcc) structure.

In hcp, the second row of spheres is placed in the interstices or depressions of the first-row spheres. The third layer is place over the second layer covering the tetrahedral voids so that spheres of third layer are exactly aligned with those of the first layer. This pattern is written as ABAB....... pattern. This structure
is called hexagonal close packed (hcp) structure