ANALYZE The density of an Fe bcc unit cell is the mass of 2 Fe atoms divided by the volume of the cell (287 pm)^3. We need to calculate the mass of 2 Fe atoms starting with the molar mass (55.84 g/mol). The conversion includes dividing by Avogadro's number to calculate the mass of each Fe atom in grams. To obtain a cell volume in cubic centimeters (cm^3), we make use of the definitions for pico-and centi-: