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# Radius/Density From bcc and fcc Unit Cells

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Krypton crystallizes as a fcc (face centered cubic unit cell) having an edge length of 559 pm.
(a.)What is the density of solid Krypton?
(b.) What is the atomic radius of a krypton atom?
(c.)What is the volume of one krypton atom?

Potassium crystallizes in a bcc (body centered cubic unit cell) structure. The atomic radius of potassium is 235 pm. Determine:
(a.) the number of atoms of potassium per unit cell, and
(b.) The length of a side of this unit cell.

Draw a pressure temperature curve for Sulfur Dioxide. Detail the areas where the material exists as solid, liquid, and as a gas. Explain what is meant by critical point, triple point, and critical temperature

#### Solution Preview

Krypton crystallizes as a fcc(face centered cubic unit cell) having an edge length of 559 pm.
(a.)What is the density of solid Krypton?
See the diagram at http://www.chem.lsu.edu/htdocs/people/sfwatkins/MERLOT/lattice/04fcc.html
From this diagram, you can see there are 8 corners, each 1/8 of an atom and 6 half atoms in the unit cell.
The number of atoms in the unit cell is (8 x 1/8) + (6 x ½) = 4 atoms per unit cell.

Density = mass/volume

Mass of Kr atoms in one unit cell = 4 atoms Kr x 83.80 g Kr = 5.566 x 10-22 g Kr/unit cell unit cell 6.022 x 1023 Kr atoms
83.80 g is the molar mass of Kr. This is divided by Avogadro's number, ...

#### Solution Summary

The solution outlines how to calculate atomic radius and density for bcc and fcc unit cells.

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