The Solid State

Question 261

Aluminum crystallizes in an fcc structure. Atomic radius of the metal is 125 pm. What is the length of the side of the unit cell of the metal? 


Aluminum crystallizes in FCC structure atomic radius (r) = 125 pm

Length of the side of the unit cell in FCC structure,  straight a equals fraction numerator 4 over denominator square root of 2 end fraction straight r space equals space 2 square root of 2 straight r end root

 Therefore            a= 2 x 1.414 x 125

a = 353.5 pm

Question 262

What are n-types semiconductors?


The semiconductor whose increased conductivity is a result of negatively-charged electrons is called an n-type semiconductor. These are generated when the crystal of a group 14 element such as Si or Ge is doped with a group 15 element such as P or As.

Question 263

Copper crystallises with face centred cubic unit cell. If the radius of a copper atom is 127.8 pm, calculate the density of the copper metal.

(Atomic mass of Cu = 63.55 u and Avogadro’s number NA = 6.02 x 1023 mol-1)


No. of atoms in unit cell, Z = 4

Radius = 127.8 pm
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Question 264

Iron has a body centred cubic unit cell with the cell dimension of 286.65 pm. The density of iron is 7.87 g cm-3. Use this information to calculate Avogadro’s number. (Atomic mass of Fe = 56.0 u)


a = 286.65 pm

= 286.65 x 10-10 cm

Density (Ï) = 7.874 g cm-3

At mass of Fe = 56.0 u

Z = 2 (For body centered cubic unit cell)

Avogadro number (N0) =?
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