# Example-1

Example-1
Ferrous oxide has a cubic structure, and each edge of the unit cell is 5.0 Ã…. Assuming the density of the oxide as , the number of Fe2+ and  ions present in each unit cell will be:
1. four  and four
2. two  and four
3. four  and two
4. three  and three
Solution (A)
Let the units of ferrous oxide in a unit cell be n and molecular weight of ferrous oxide .

Weight of n units

Volume of one unit = (Length of corner)3

Density

# Example-2

Example-2
In a solid AB having the  structure, A atoms occupy the corners of the cubic unit cell. If all the face-centered atoms along one of the axes are removed, then the resultant stoichiometry of the solid is:
Solution (D)
There are 6 A atoms on the face centers. Removing face-centered atoms along one of the axes means removal of 2 A atoms. Now,

Number of A atoms per unit cell

Number of B atoms per unit cell  +

Hence, the resultant stoichiometry is .

# Example-3

Example-3
The edge length of face centered unit cubic cell is  If the radius of the cation is  the radius of the anion is:
Solution (C)
Distance between centers of cation and anion

or  or

# Example-4

Example-4
The number of atoms in 100 g of an fcc crystal with density  and cell edge equal to  is equal to:
Solution (A)

Number of atoms in 100 g

# Example-5

Example-5
The number of unit cells in 58.5 g of  is nearly:
Solution (C)

One unit cell contains  units. Hence,

Number of unit cell present