十万个为什么·科学启蒙30篇（4）

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为什么金属通常是导电的

Metals have a 'sea' of delocalized valence electrons that move freely among fixed positive metal ions.
When voltage is applied, these electrons drift directionally, carrying current with little resistance.
Crystalline structure matters: defects or impurities scatter electrons, increasing resistance and heating the wire.
Silver conducts best, followed by copper and gold—but copper is widely used for cost and stability reasons.
Alloys like brass conduct worse than pure metals because added atoms disrupt the electron flow path.
At low temperatures, some metals become superconductors—resistance drops to zero as electrons pair up and move smoothly.
Unlike insulators, whose electrons are tightly bound, metals require minimal energy to start current flow.
This electron mobility also explains why metals reflect light and feel cold—they transfer thermal energy efficiently too.