ENGR 100 Lecture Notes - Lecture 27: Atomic Packing Factor, Metal, Face Diagonal
Document Summary
Unit cell a prism having three sets of parallel faces, in most cases a cube, but it is chosen based on the symmetry of the crystal structure. The unit cell is simply the basic structural unit or building block of the crystal structure and defines the crystal structure with its geometry and the atom positions within. Atoms are located at each of the corners and the centers of all cube faces. The spheres, or ion cores touch each other across a face diagonal. Metals having this structure include: copper, aluminum, silver, gold. The cube edge length a and the atomic radius r are related by: From the picture you can see that each corner atom would be shared among 8 unit cells. The atoms on the faces belong to two unit cells. Combined, there is a total of 4 atoms in the fcc unit cell.
