What changes the chemical and physical properties of a metal's crystal structure?

• A. Heat Treatment
• B. Defects
• C. Grain Size
• D. Alloying

Answer: (B)

Defects in the metal’s crystal lattice are what directly change its chemical and physical properties. An imperfect lattice—with missing atoms (vacancies), extra atoms in interstitial spots, or misaligned regions (dislocations)—disturbs the regular bonding and how atoms interact. That disruption changes how electrons move, how easily atoms can swap positions, and how the material responds to stress. As a result, properties such as strength, hardness, ductility, diffusion rates, and even corrosion resistance are altered.

Grain boundaries act as another kind of defect that affects behavior by hindering or guiding dislocation motion, which also shifts mechanical properties. While heat treatment, grain size, and alloying can certainly influence these properties, they do so largely by changing the defect structure and grain arrangements. The presence and nature of defects are the central factor that directly modify the crystal structure’s properties.