Mechanical Engineering Material

Valence electrons are detached from atoms and spread in an ''electron sea'' that glues the ions together. Metals are usually strong conduct electricity and heat well and are opaque to light (shiny if polished).Examples: aluminum steel brass gold.The bonding is covalent (electrons are shared between atoms). Their electrical properties depend extremely strongly on minute proportions of contaminants. They are opaque to visible light but transparent to the infrared. Examples: Si Ge GaAs...