# Exercise 9 | Liquids and Solids

Chromium has a body-centered cubic lattice with a density of 7.20 g.cm-3.

What is the length of an edge of a unit cell?

d = $\frac{\mathrm{M}}{{\mathrm{V}}_{\mathrm{mol}}}$

d = density (g.m-3)

M = mass molar (g.mol-1)

Vmol = molar volume (m3.mol-1)

Vmol =

Vunit cell = unit cell volume (in m3)

N = number of atom s in a unit cell

NA = Avogadro’s number = 6.022 x 1023 mol-1

⇒ d = $\frac{\mathrm{M}}{{\mathrm{V}}_{\mathrm{mol}}}$

⇒ Vmol = $\frac{\mathrm{M}}{\mathrm{d}}$

⇒ Vunit cell =

Body-centered cubic lattice: 2 atoms per unit cell ⇒ N = 2

⇒ Vunit cell =

⇒ Vunit cell = 2.40 x 10-29 m3

If L = length of the edge

⇒ Vunit cell = L3

⇒ L = 2.88 x 10-10 m = 288 pm