Chapter 12.3, Problem 21SSC

Interpretation Introduction

Interpretation:

A unit cell and crystal lattice must be compared.

Concept introduction:

Lattices are the arrangements of atoms.

Answer to Problem 21SSC

A unit cell is the smallest repeating unit in the crystal lattice.

Explanation of Solution

A unit cell is always small which is a part of the crystal lattice. A unit cell has lesser number of atoms. For example a cubic crystal has 8 atoms at the 8 corners. But number of atoms in the unit cell is only 1.

This is because all the corner atoms are contributing only 1/8 th portion of the spherical atom o the unit cell.

Thus number of atoms per unit cell $=8\times \frac{1}{8}=1.$

Conclusion

A unit cell is the smallest repeating unit of the whole crystal lattice.