NEET Chemistry The Solid State Questions Solved

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The density of lead is 11.35 g cm-3 and the metal crystallizes with fcc unit cell. Estimate the radius of lead atom.

(At. mass of lead = 207 g mol-1 and NA = 6.02×1023 mol-1)

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Concept Questions :-

Density/Formula/packing fraction/ Semiconductors

Given : d = 11.35 g cm-3

According to the formula

d = Z×Ma3×NA     or a3Z×Md×NA

For fcc lattice, Z = 4

a34×207 g mol-111.35 g cm-3×6.02×1023mol-1

or a3 82868.327×1023 = 12.118 ×10-23

or a3 = 1.212×10-22 cm3

or a = 1.212×10-223 cm3

 a = 4.95×10-8 cm

For fcc unit cell, r = a22

or r = 4.95×10-82×1.414 = 4.95×10-82.828

 Radius, r = 1.75×10-8 cm = 175 pm

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