The crystal structure of an element X can be described as follows: X atoms form

Question

The crystal structure of an element X can be described as follows: X atoms form a face-centred cubic lattice with an edge length of 356.7 pm. In addition, there are X atoms occupying every other tetrahedral site in the face-centred cubic lattice. The density of the solid is found to be 3.52 g/cm3. What is the molar mass of the element, in g/mol?

Note: The X atoms form a face-centred cubic lattice with an edge length of 356.7 pm, but the lattice is not closest-packed.

Enter your answer accurate to 3 significant figures. Do not include units as part of your answer.

Explanation / Answer

number of x atoms per unit cell = 4 (fcc) + 4( tetrahedral voids) = 8 density = nM/NV 3.52 = 8 x M/(6.023 x10^23) (356.7 x10^-10)^3 M = 12.027 gm

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