Question

Which of the following statement(s) regarding hexagonal closed packing in 2D is/are correct?

• A. The coordination number of hcp in 2-D is 6
• B. ABAB... pattern gives hexagonal closed packing in 2-D
• C. Triangular shape empty spaces or voids are present in hcp
• D. In hcp, second row of spheres is placed adjacent to first row

Answer 1

Answer: (A), (B), (C)

Triangular shape empty spaces or voids are present in hcp

Hexagonal close packing in 2-D
Here, the second row of spheres is placed in the interstices or depressions of the first-row spheres. Thus, it gives ABAB... type arrangement.

In this arrangement some triangular shaped, empty spaces are present.​ These are called triangular voids.


Each sphere touches 6 other neighbours. Thus, its coordination number is 6.
The centres of the neighboring spheres join to form a hexagon.​ So, the packing is known as hexagonal close packing in 2-D.
Thus, statement (a), (b) and (c) are correct.