Question

What is the coordination number of atoms in cubic closed pack structure?

Answer 1

Cubic close pack structure:

1. In the crystal structure, the number of atoms surrounding and touching a central atom is referred to as the Coordination number.
2. There are three layers in a cubic close-packed structure. The first and fourth layers are the same. It's of the 'A, B, C, A, B, C' pattern. The first layer contains 3 atoms, the second layer or middle layer contains six atoms, and the third layer contains three atoms as well.
3. Each of the eight corners ($8\times \frac{1}{8}=1$ atom from the corners) has one-eighth part of an atom, and each of the six faces has one-half of an atom ($6\times \frac{1}{2}=3$ atoms from the faces).
4. With the cube face diagonal, the atoms in the corners touch the atoms in the centers of adjacent faces.
5. Each atom in a cubic close-packed arrangement is in contact with $12$ other atoms.

Therefore, the Cubic close-packed structure has a coordination number$=12$