Argon cubic closest packing

Cuthbert and Linnett80 have suggested that the stability of the cubic closest packed arrangement of atoms in crystals of neon, argon, krypton, and xenon (helium crystallizing instead in hexagonal closest packing)81 is explicable by the tetrahedral electron distribution of the atoms... 

Argon has a cubic closest packed structure as a solid. Assuming that argon has a radius of 190. pm, calculate the density of solid argon. 

Figure 12.29 Cubic closest packing of frozen argon (face-centered cubic unit cell).

The structure of crystals can be investigated by the electron-diffraction method as well as by the x-ray-diffraction method. The electron-diffraction method has been especially useful in studying the strueture of very thin films on the surface of a crystal. For example, it has been shown that when argon is adsorbed on a clean face of nickel crystal the argon atoms occupy only one-quarter of the positions formed by triangles of nickel atoms (in the octahedral face of the cubic closest-packed crystal Figure 2-7). The structure of very thin films of metal oxide that are formed on the surface of metals, and that protect them against further corrosion, has been studied by this method. 

Neon, argon, krypton, and xenon crystallize in cubic closest packing (Section 2-4), with a = 452, 543, 559, and 618 pm, respectively. To what values of the density do these values of the edge of the unit cube correspond ... 

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