Lithium has a bcc structure. Its density is 530 kg m⁻³ and its atomic mass is 6.94 g mol⁻¹. Calculate the edge length of a unit cell of Lithium metal: (NA = 6.02 × 10²³ mol⁻¹)

Density, d = 530 kg/m³ = 0.530 g/cm³ (≈ 1 kg/m³ = 10⁻³ g/cm³)
Molar atomic mass, M = 6.94 g/mol
For bcc unit cell, the number of atoms per unit cell, Z = 2
Density, d = ZM/a³NA
0.530 = 2 × 6.94/a³ × 6.023 × 10²³
a³ = 4.34 × 10⁻²³
⇒ a = 3.52 × 10⁻⁸ cm
The edge length, a = 3.52 × 10⁻⁸ cm = 352 × 10⁻¹⁰ m = 352 pm (≈ 1 m = 100 cm and 1 pm = 10⁻¹² m)