Cs crystallizes in a body-centered cubic arrangement. Assuming that the dimensions of the unit cell for Cs and for CsCl are equivalent, determine the ratio of the density of Cs to the density of CsCl.
A) 1.58
B) 2.79
C) 1.00
D) 0.789
E) none of these

Question

Quizplus · Accepted Answer

The density of a crystal is directly proportional to the mass of the atoms in the unit cell and inversely proportional to the volume of the unit cell. For Cs and CsCl, the unit cells are equivalent in size, so the ratio of their densities is equal to the ratio of the masses of their atoms. The atomic mass of Cs is 132.91 amu, and the atomic mass of Cl is 35.45 amu. Therefore, the ratio of the density of Cs to the density of CsCl is 132.91 amu / (132.91 amu + 35.45 amu) = 1.58.

Cs Crystallizes in a Body-Centered Cubic Arrangement