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Why does copper conduct electric current well?

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density current: descent to the ocean floor — density current Diagram showing the behaviour of a density current as it descends to the seafloor.

Copper is an excellent electrical conductor primarily due to the nature of its metallic bond, which allows its valence electrons to become non-localized. In copper, these electrons are not bound to any specific atom but instead form a "cloud" or gas that is free to move throughout the crystal structure when an electric field is applied.123

The efficiency of this conduction depends on both the number of these free electrons and their mobility—the ease with which they can travel through the solid. Copper is particularly effective because it possesses low electrical resistance, meaning that as electrons move, they experience relatively few collisions with ions or crystal defects that would otherwise scatter them and convert their kinetic energy into heat.452

Furthermore, the purity of the metal is critical; impurities can disrupt the crystal lattice and interfere with electron movement, which is why pure copper is significantly more conductive than copper alloys.4

Note: The concept of a "density current" in physics typically refers to fluid dynamics involving differences in density, rather than the flow of electric charge in metals.