# Metallic Crystals - The Structures of Pure Metals

## The Body-Centered Cubic Lattice

Tab.1
Wireframe modelSpace-filling model
Fig.1
Fig.2

Both models show that the central red sphere in the unit cell is coordinated by eight gray spheres.

Hint
The red and gray spheres are fully equivalent, the different colors are only used for clarification.

The third important metallic crystal structure is the body-centered cubic lattice. The coordination number is 8. This seems to be considerably lower than the coordination number of the closest-packed structures. However, when you take into account that the next following neighbors (across the face centers of the cube) are only 1.15 ($2/ 3$) times farther away than the closest spheres, the coordination number becomes 14. This means that the coordination number is effectively not very different from that of the closest-packed structures. This is confirmed by the fact that 68 % of the space is occupied.

The figures illustrate the unit cells of a body-centered cubic lattice and a face-centered cubic lattice.

Fig.3
Body-centered cubic unit cell
Fig.4
Face-centered cubic unit cell
Page 7 of 11