LiF has the same unit cell as NaCl (fcc). The edge length of the LiF unit cell is 402 pm. Determine the density of LiF in g/cm3.

Answer 1

density = Z x M / N_o x a³

Z = 4 atoms = # of atoms in a fcc unit cell

M = atomic mass = 25.94 g/mol

N_o = Avogadro's number = 6.02x10²³ atoms / mol

a = edge length in cm = 402 pm x 10^-10 cm / pm = 402x10^-10 cm

density = (4 atoms)(25.94 g/mol) / (6.02x10²³ atoms/mol)(402x10^-10 cm)³

density = 2.65 g / cm³

(please be sure to check the math)