What causes metals to be lustrous?

Metals are lustrous due to their ability to reflect light from their surface, a property known as metallic lustre.

The lustre or shine of metals is a characteristic property that sets them apart from non-metals. This is primarily due to the unique structure of metals at the atomic level. Metals have a sea of free electrons, also known as delocalised electrons, which are not attached to any particular atom and can move freely throughout the metal.

When light falls on the surface of a metal, these free electrons absorb the energy from the light. This energy excites the electrons, causing them to vibrate. As they return to their normal state, they release this energy in the form of light, which is reflected off the surface of the metal. This reflection of light is what gives metals their characteristic shine or lustre.

Furthermore, the ability of metals to reflect all wavelengths of light equally well contributes to their shiny appearance. Unlike certain non-metals which may absorb certain wavelengths and reflect others (giving them a coloured appearance), metals reflect all wavelengths equally, resulting in a white or silver shine.

In addition, the smoothness of a metal surface can enhance its lustre. A smooth surface provides a more uniform platform for the reflection of light, thereby increasing the intensity of the reflected light and making the metal appear shinier. This is why polished metals appear more lustrous than unpolished ones.

In summary, the lustre of metals is a result of their unique atomic structure, their ability to reflect all wavelengths of light, and the smoothness of their surface.