Copper is located in group 11 of the periodic table, along with silver and gold, and the common characteristics of these metals include high ductility and good electrical conductivity. The atoms of these elements have only one electron in the outermost layer, located in the s sublayer, and a full complement of electrons in the d sublayer of the second outer layer. Interactions between atoms are dominated by metallic bonds formed by electrons in the s sublayer, while the full d sublayer has little effect. Unlike the metal atoms in the underfilled d sublayer, the covalent component of metallic bonding in copper is small and weak, resulting in low hardness and high ductility of single-crystal copper. Macroscopically, widespread defects in the lattice (e.g., grain boundaries), which impede the flow of the material under applied pressure, increase the hardness. As a result, it is common for copper to be fine-grained polycrystalline (English: polycrystal), which is harder than single-crystal copper.
Copper is not only soft, electrical conductivity (59.6 × 10 6 S/m), thermal conductivity (401W/(m-K)) is also good, at room temperature in the metal monomers after silver. This is because at room temperature, the copper is more hard than single-crystal copper. [7] This is due to the fact that the resistance to electron motion in metals at room temperature comes mainly from scattering of electrons due to thermal vibrations of the lattice, whereas scattering is weaker in softer metals. The maximum current density allowed for copper in the open air is 3.1 × 10 6 A/m 2 (cross-section), and larger currents will overheat it. [8] Like other metals, copper undergoes galvanic corrosion when juxtaposed with other metals.
Copper is one of four metallic elements whose natural color is not gray or silver; the other three are cesium, gold (yellow), and osmium (blue). [10] Pure copper is a single element that is not gray or silver. Pure copper monomers are reddish-orange in color, but lose their luster and turn red when exposed to air. This particular color of copper is due to electron transitions between the full 3d sublayer and the half-full 4s sublayer – the energy difference between these two sublayers corresponds to orange light. Cesium and gold are yellow by the same principle.
