The well known mineral fluorite is chemically calcium fluoride. It is known that in one unit cell of this mineral there are 4 Ca2+ ions and 8 F- ions and that Ca2+ ions are arranged in a fcc lattice. The F- ions fill all the tetrahedral holes in the face centred cubic lattice of Ca2+ ions. The edge of the unit cell is 5.4610-8 cm in length. The density of the solid is 3.18 g cm-3. Use this information to calculate Avogadro's number (Molar mass of CaF2 = 78.08 g mol-1).
Edge of the unit cell (a) = 5.4610-8 cm
Density (P) = 3.18 g cm-3
According to the formula :
NA = NA =
NA = = 6.0331023