- Gold (Au) is a highly prized transition metal with atomic number 79, belonging to Group 11 of the periodic table, alongside copper and silver.
- Its electron configuration is [Xe] 4f¹⁴ 5d¹⁰ 6s¹, giving it a filled d-subshell and a single s-electron that contributes to its metallic bonding and chemical behavior. Each atom of gold contains seventy-nine protons, seventy-nine electrons, and typically 118 to 126 neutrons depending on the isotope.
- Naturally occurring gold consists almost entirely of a single stable isotope, gold-197 (¹⁹⁷Au).
- Gold has been known and treasured since prehistoric times, making it one of the first metals used by humans. Ancient civilizations such as the Egyptians, Mesopotamians, and Chinese used gold for jewelry, coins, and religious artifacts. Its rarity, luster, malleability, and resistance to tarnish gave it cultural and symbolic value across millennia. Alchemists in the Middle Ages famously sought to transmute base metals into gold, a pursuit that contributed to the development of modern chemistry.
- Physically, gold is distinct for its bright yellow metallic luster, which results from relativistic effects on its electron structure, causing unusual absorption and reflection of light. It is one of the most malleable and ductile metals known: a single gram of gold can be beaten into a sheet of nearly one square meter, and one ounce can be drawn into a wire over 80 kilometers long. Gold has a density of 19.32 g/cm³, a melting point of 1,064 °C (1,947 °F), and a boiling point of 2,856 °C (5,173 °F).
- Chemically, gold is classified as a noble metal due to its extraordinary resistance to oxidation and corrosion. It does not react with oxygen or water under normal conditions, and it remains unaffected by most acids. However, it dissolves in aqua regia, a mixture of hydrochloric and nitric acids, forming chloroauric acid (HAuCl₄). Gold exhibits oxidation states ranging from –1 to +5, though +1 and +3 are the most common in compounds. Examples include gold(I) chloride (AuCl) and gold(III) oxide (Au₂O₃).
- Gold’s uses are both traditional and technological. Historically, it has been used in jewelry, coinage, and as a standard for monetary systems. In modern applications, gold’s excellent conductivity, resistance to tarnish, and biocompatibility make it indispensable in electronics, dentistry, and medicine. It is used in connectors, switches, and thin films for microchips. In dentistry, gold alloys remain valued for crowns and fillings due to their durability. In medicine, gold compounds such as auranofin have been used in the treatment of rheumatoid arthritis, while gold nanoparticles are being studied for applications in drug delivery, imaging, and cancer therapy.
- Biologically, gold has no known essential role in living organisms. Metallic gold is inert and non-toxic, but some soluble gold compounds can be harmful. Interestingly, trace amounts of gold are present in the human body, though they have no biological function.
- Environmentally, gold is a rare element in Earth’s crust, with an average abundance of about 0.004 parts per million. It is primarily found in native form, often associated with quartz veins, placer deposits, and sulfide ores. Major producers include China, Australia, Russia, the United States, and South Africa. Gold mining, while economically important, has significant environmental impacts, particularly when mercury or cyanide is used in extraction processes. Efforts are ongoing to improve recycling and develop more sustainable recovery methods.
