Crystal Density

A unit cell is the smallest repeating unit of a crystal lattice. The edges are labeled a, b, and c. The angles between them are α, β, and γ.

The lattice type determines the number of atoms or formula units present inside one unit cell. This number is represented by Z. For a primitive cell, Z is 1, for a body-centered cubic cell, Z is 2, and for a face-centered cubic cell, Z is 4.

To calculate the crystal density, ρ, we need its mass and volume.

The mass of a unit cell equals Z, multiplied by the molar mass, M, and divided by Avogadro’s number, N_A.

For a right-angled unit cell, the volume equals the product of its edge lengths. Now, divide the mass by its volume to get the crystal density of the unit cell.

If molar mass is given in grams per mole, and the edge lengths are in centimeters, the density is reported in grams per cubic centimeter.

So, crystal density depends on the number of particles inside the unit cell and the unit cell dimensions.