Short Answer:

Metals have metallic lustre because their atoms have free electrons that can reflect light. When light falls on a metal surface, these free electrons vibrate and reflect the light, giving metals a shiny appearance.

This property makes metals attractive and useful in jewelry, decorative items, and coins. The metallic lustre is a characteristic feature that helps distinguish metals from nonmetals, which usually have a dull appearance.

Detailed Explanation:

Metallic Lustre

Metallic lustre refers to the shiny, reflective surface seen in metals. This property is one of the key physical characteristics of metals and is easily observed in freshly polished or clean metal surfaces.

Cause of Metallic Lustre

• Metals consist of atoms arranged in a regular lattice structure with free or delocalized electrons.
• These free electrons are not bound to any particular atom and can move easily across the metal.
• When light strikes the metal surface, free electrons absorb and re-emit the light energy, reflecting it back.
• This reflection of light gives metals their bright, shiny appearance known as metallic lustre.

Factors Affecting Lustre

1. Clean Surface:
   • Metals show the best lustre when their surfaces are clean and free from oxides or dirt.
   • For example, silver tarnishes over time and loses its shine due to reaction with sulfur in the air.
2. Polishing:
   • Polished metals reflect light better and appear more lustrous.
   • Jewelry, coins, and decorative metal items are often polished to enhance metallic lustre.
3. Type of Metal:
   • Metals like gold, silver, and copper have strong metallic lustre and are used for decorative purposes.
   • Other metals like iron or lead have less shine but still show metallic reflection.

Importance of Metallic Lustre

• Aesthetic Value: Metals with lustre are used in jewelry, coins, and ornaments.
• Identification: Metallic lustre helps distinguish metals from nonmetals, which appear dull or glassy.
• Industrial Use: Lustrous metals can be coated, polished, and used in mirrors, instruments, and machinery.

Comparison with Nonmetals

• Nonmetals do not have free electrons in the same way as metals.
• They cannot reflect light efficiently, so they appear dull, brittle, or glassy.
• This difference in lustre is a key physical property used to classify elements.

Summary

• Metallic lustre is due to free electrons in the metallic lattice.
• It is enhanced by a clean, polished surface.
• Metals with strong lustre are widely used in decorative, industrial, and functional applications.

Conclusion:

Metals have metallic lustre because their free electrons reflect light from their surface. This gives metals a shiny and attractive appearance, distinguishing them from nonmetals. Metallic lustre is important in jewelry, decoration, identification of metals, and various industrial applications.