Ar is a solid below -189 oC with a face-centered cubic array of atoms and a supposed density of 2.29 g/cm3. Assuming that the atoms are spheres in contact along the face diagonal, what is the radius of a Ar atom (in Angstroms)? An angstrom = 10-10 m or 10-8 cm. Hint, first find the length of an edge of the unit cell