Given Values: The edge length a=288pm. The density (ρ) is 7.2g∕cm3. The mass given is 208 g . Step 1: Find volume of one unit cell The edge length must be changed to centimeters: 1pm=10−10cm. So: a=288×10−10cm. The volume of one unit cell is: V=a3=(288×10−10)3cm3=2.389×10−23cm3 Step 2: Find total volume that 208 g will occupy Vtotal =
m
ρ
=
208
7.2
=28.89cm3 Step 3: Find the number of unit cells in 208g Number of unit cells =
Vtotal
Vunit cell
=
28.89
2.389×10−23
=1.209×1024 Step 4: Find the total number of atoms A body centered cubic (bcc) unit cell has 2 atoms per unit cell. So, Total atoms = Number of unit cells ×2=1.209×1024×2=2.42×1024 which is the same as 24.2×1023.
