Lead (pb) has a density of 11.3 g/cm3 and crystallizes face-centered cubic. based on these data, calculate the radius (r) of the lead atom given that, for a face-centered unit cell: cube edge length = r√8.

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Chemistry

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3 June, 07:24

Lead (pb) has a density of 11.3 g/cm3 and crystallizes face-centered cubic. based on these data, calculate the radius (r) of the lead atom given that, for a face-centered unit cell: cube edge length = r√8.

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Sidney Knapp · Answer 1

Lead is said to have a face centered cubic crystal structure. So, it would have four atoms per cell where 3 of the atoms are at the faces and 1 atom constitutes the corner of the unit cell. So, that the diagonal of one face of the cell is equal to 4 times the radius. To determine the measurement of the radius, we calculate the volume from the density given.

Density = 11.3 g / cm^3 = 207.2 g / mol (4 atoms / cell) / 6.022x10^23 atoms / mol (V cm^3 / cell)

Calculating for V,

V = 1.21795 x 10^-22 cm^3

V = a^3 where a is the edge length

a = ∛1.21795 x 10^-22 cm^3

a = 4.9569x10^-8 cm

diagonal = 4r

r = diagonal / 4

where diagonal = √2a^2 = a√2

r = a√2 / 4 = 1.7525x10^-8 cm