The unit cell edge length of a cubic system is calculated using the density of the crystal. Let ‘a’ be the edge length (or primitive) of a cubic unit cell and ‘ρ’ be the density of the crystal.
The mass of the unit cell = ρa3 _____ (2.1)
Let ‘M’ be the molecular weight and NA be the Avogadro number (i.e., number of molecules per kg mole of the substance) of the crystal.
Then, mass of each molecule =
If each unit cell contains n molecules (or lattice points),
Then the mass of unit cell = n ____ (2.2)