reviewing...walk me through it?

Question

MnO has either the NaCl type structure or the CsCl type structure. The edge length of the MnO unit cell is 4.47*10^-8 cm and the density of MnO is 5.28 g/cm^3.
a) Does MnO crystalize in the NaCl or CsCl structure?
b) assuming that the ionic radius of oxygen is 140 pm. estimate the ionic redius of manganese.

For the structures it refered mo to this question....The CsCl structure is a simple cubic array of chloride ions with a cesium ion at the center of each cubic array. Given that the density of cesium cholride is 3.97 g/cm^3 and assuming that the chloride and cesium ions touch along the body diagonal of the cubic unit cell. calculate the distance between the centers of adjacent Cs+ and Cl- ions in the solid. Compare this value with the expected distance based on the sized of the ions. The ionic radius of Cs+ is 169 pm and the ionic radius of Cl- is 181 pm.

Thanks im trying to review and don't know what to do for this one...if you could help it would be great :]

Answer 1

Principle: density = mass/volume.

You know the volume (cube of cell edge), so it's the mass you're after.

Work out the number of formula units per unit cell in each of the two possible structures. Hence work out the mass per unit cell in amu, divide by Na to get the mass in g, and then divide by the volume per unit cell (= edge^3, since these structures have cubic symmetry) to get the predicted density. Compare the two predictions with what is observed.

Answer 2

Ionic Radius Oxygen