Question

What is the coordination number in body centered cubic (BCC) arrangement of identical particles?

Answer 1

Unit cell:

1. It is the main portion of a crystal lattice that is repeated in any direction.
2. It has a three-dimensional structure in which sides are represented as a, b, and c and also angles $\mathrm{\alpha },\mathrm{\beta },\mathrm{and}\mathrm{\gamma }$.
3. $\mathrm{\alpha }$ is the angle between b and c, $\mathrm{\beta }$ is the angle between a and c, and $\mathrm{\gamma }$ is the angle between a and b.
4. The diagram of a unit cell is shown below:

Figure: Parameters of a unit cell.

Body-centred cell (BCC):

1. A unit consists of particles at the corner position of the cell and also contains one more particle at the centre of the unit cell.
2. All three edges are of equal length (a=b=c) and also all the angles ($\mathrm{\alpha },\mathrm{\beta },\mathrm{and}\mathrm{\gamma }$) are $90°$.
3. The examples of body-centred cells are $\mathrm{NaCl},\mathrm{Cu},\mathrm{and}\mathrm{Zn}\mathrm{blende}$.

Body-centred unit cell:

1. Lattice point at corners ($8\times \left(\frac{1}{8}\right)=1$), so 1 atom
2. Lattice point at the centre ($1\times 1=1$), so 1 atom
3. The total number of atoms per unit cell is 2 atoms

Body-centred coordination number:

1. Lattice point present at top = 4atoms
2. Lattice point present at bottom = 4atoms
3. The Center lattice point is surrounded by a total eight number of lattice points.

Figure: Body-centered unit cell