# 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)

Concept Videos :-

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#24 | Density of Unit Cell

Concept Questions :-

Density/Formula/packing fraction/ Semiconductors

Given : d = 11.35 g cm-3

According to the formula

d = $\frac{Z×M}{{a}^{3}×{N}_{A}}$     or a3$\frac{Z×M}{d×{N}_{A}}$

For fcc lattice, Z = 4

a3

or a3 $\frac{828}{68.327×{10}^{23}}$ = 12.118 $×$10-23

or a3 = 1.212$×$10-22 cm3

or a = $\sqrt[3]{1.212×{10}^{-22}}$ cm3

$\therefore$ a = 4.95$×$10-8 cm

For fcc unit cell, r = $\frac{a}{2\sqrt{2}}$

or r = $\frac{4.95×{10}^{-8}}{2×1.414}$ = $\frac{4.95×{10}^{-8}}{2.828}$

$\therefore$ Radius, r = 1.75$×$10-8 cm = 175 pm

Difficulty Level:

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