Question

What do you understand by point defects?

Hint:

Point defects disturb the arrangement at specific points; line defects disturb along an entire row of atoms.

Answer 1

Step 1: Definition.
Point defects are irregularities or deviations from the ideal arrangement of atoms or ions at specific lattice points in a crystalline solid.
Step 2: Explanation.
They occur due to the absence, displacement, or presence of extra atoms or ions at lattice sites. These defects affect the physical and electrical properties of the crystal.
Step 3: Types of point defects.
1. Stoichiometric defects – e.g., Schottky and Frenkel defects.
2. Non-stoichiometric defects – due to excess or deficiency of ions.
3. Impurity defects – caused by foreign atoms.
Step 4: Example.
In NaCl crystal, when equal numbers of Na$^+$ and Cl$^-$ ions are missing from their lattice sites, it produces a Schottky defect.