Stainless steel is everywhere in our daily lives, and there are many different grades—many people often have trouble telling them apart. They may not know which grades are suitable for specific applications or which grade is considered high-quality.

Copper(I) is commonly referred to as cuprous copper; cuprous chloride (CuCl), cuprous oxide (Cu₂O), and cuprous sulfide (Cu₂S) are all common monovalent copper compounds. [Cu(NH₃)₂]²⁻ is a complex ion formed by cuprous copper and ammonia; it is colorless, easily oxidized, and spontaneously dissociates in acidic solutions to form Cu(II) and Cu.

Copper is a non-ferrous metal that plays a vital role in human life. It is widely used in the electrical, light industrial, machinery manufacturing, construction, and defense industries, and ranks second only to aluminum in terms of consumption among non-ferrous metals in China. Copper is a red metal, but it is also considered a “green” metal. It is called a “green” metal primarily because it has a low melting point, making it easy to remelt and re-smelt, and therefore relatively inexpensive to recycle.

Native copper. Copper ore with a copper content of around 1% (0.5%–3%) is considered economically viable for mining, because flotation can be used to remove some of the gangue and other impurities from the ore, yielding a concentrate with a higher copper content (8%–35%).

Pure copper is a rose-red metal that turns purple when a layer of copper oxide forms on its surface; therefore, industrial-grade pure copper is often referred to as red copper or electrolytic copper. It has a density of 8–9 g/cm³ and a melting point of 1083 °C.

Copper, with the chemical symbol Cu, has an atomic mass of 63.54, a density of 8.92, and a melting point of 1083°C. Pure copper is pale rose or light red in color; once a layer of copper oxide forms on its surface, it takes on a copper-red appearance.