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Gold is virtually insoluble, except in aqua regia.
Gold exists in three primary forms, elemental, Au (I), and Au (III).
As a precious metal, Gold is resistant to ionization and generally considered biologically benign in its elemental state.
CAS: 7440-57-5
MF: Au
MW: 196.97
EINECS: 231-165-9
Synonyms
Gold wire, 0.2mm dia., 99.9% trace metals basis;GOLD ICP/DCP STANDARD;GOLD ICP STANDARD;GOLD ULTRATHIN;GOLD SOL;GOLD SPLATTER;GOLD SPONGE;GOLD STANDARD
Gold is not permitted for use in foods, drugs or cosmetics as a coloring agent in the U.S. However, surface decoration of foods under conditions which preclude consumption is not considered to be a food use and is, therefore, exempt from regulations concerning food use.
The use of gold in the decoration of food is more popular in Europe, where, probably as the result of its limited use, its use has been accepted.
Gold is the 72nd most abundant element and is widely spread around the world, but it is not evenly distributed through the surface of the Earth.
Gold is usually found in a few concentrated regions, sometimes in pure flake and nugget metallic forms.
Most of Gold exists in conjunction with silver ore, quartz (SiO2), and the ores of tellurium, zinc, and copper.
About one milligram of gold exists in every ton of seawater (this is about 10 parts of gold per trillion parts of seawater, which amounts to a total of about 79 million tons of gold in solution).
No economical method of extracting gold from seawater has been developed to recover this treasury of the sea.
Free metallic gold is found in veins of rocks and in ores of other metals.
Alluvial gold (placer deposits) is found in the sand and in the gravel at the bottom of streams where it has been deposited as a result of the movement of water over eons.
Most gold is recovered from quartz veins called loads and from ores that are crushed.
Metallic element of atomic number 79, Group IB of the periodic table, aw 196.9665, valences of 1, 3; no stable isotopes.
A transition metal that occurs native.
Gold is unreactive and is very ductile and malleable.
Gold is used in jewelry, often alloyed with copper, and in electronics and colored glass.
Pure gold is 24 carat; 9 carat indicates that 9 parts in 24 consist of gold.
Symbol: Au; m.p. 1064.43°C; b.p. 2807°C; r.d. 19.320 (20°C); p.n. 79; r.a.m. 196.96654.
Symbol Au.
A soft yellow malleablemetallic transition element;a.n. 79; r.a.m. 196.967; r.d. 19.32;m.p. 1064.43°C; b.p. 2807±2°C.
Goldhas a face-centred-cubic crystal structure.
Gold is found as the free metal ingravel or in quartz veins, and is alsopresent in some lead and copper sulphideores.
Gold also occurs combinedwith silver in the telluride sylvanite,(Ag,Au)Te2.
Gold is used in jewellery,dentistry, and electronic devices.
Chemically, Gold is unreactive, beingunaffected by oxygen.
Gold reacts withchlorine at 200°C to form gold(III)chloride.
Gold forms a number of complexeswith gold in the +1 and +3 oxidationstates.
Gold nanoparticles PEG 5000 biotin terminated.
The preparation of biotinylated gold nanoparticles involves two surface modification steps.
First, the carboxyl-terminated alkanethiol is attached to the surface of gold nanoparticles via chemisorption in the presence of a stabilizing agent.
This step is followed by the reaction of the carboxyl groups with (+)-biotinyl-3,6,9,-trioxaundecanediamine and 2-(2-aminoethoxy)ethanol.
Gold nanoparticles have one-of-a-kind properties turn them to ideal for detecting even the smallest amounts of biological molecules.
These particles can be loaded with drugs or other therapeutic agents and then targeted to specific cells/tissues.
Further to their diagnostic applications, gold nanoparticles may also take part in drug delivery and cancer therapy.
Colloidal Gold is purified by proprietary chromatographic techniques.
Gold is a chemical element; its chemical symbol is Au (from Latin aurum) and atomic number 79.
In its pure form, it is a bright-metallic-yellow, dense, soft, malleable, and ductile metal.
Chemically, gold is a transition metal, a group 11 element, and one of the noble metals.
Gold is one of the least reactive chemical elements, being the second lowest in the reactivity series, with only platinum ranked as less reactive.
Gold is solid under standard conditions.
Gold often occurs as the free element (native state), as nuggets or grains, in rocks, veins, and alluvial deposits.
Gold occurs in a solid solution series with the native element silver (as in electrum), naturally alloyed with other metals such as copper, platinum, and palladium, as well as mineral inclusions such as within pyrite.
Less commonly, Gold occurs in minerals as gold compounds, often with tellurium (gold tellurides).
Gold is resistant to most acids, though it does dissolve in aqua regia (a mixture of nitric acid and hydrochloric acid), forming a soluble tetrachloroaurate anion.
Gold is insoluble in nitric acid alone, which dissolves silver and base metals, a property long used to refine gold and confirm the presence of gold in metallic substances, giving rise to the term "acid test".
Gold dissolves in alkaline solutions of cyanide, which are used in mining and electroplating.
Gold also dissolves in mercury, forming amalgam alloys, and as the gold acts simply as a solute, this is not a chemical reaction.
A relatively rare element when compared to silver (though thirty times more common than platinum), gold is a precious metal that has been used for coinage, jewelry, and other works of art throughout recorded history.
In the past, a gold standard was often implemented as a monetary policy.
Most gold coins ceased to be minted as a circulating currency in the 1930s, and the world gold standard was abandoned for a fiat currency system after the Nixon shock measures of 1971.
In 2023, the world's largest gold producer was China, followed by Russia and Australia.
As of 2020, a total of around 201,296 tonnes of gold exist above ground.
If all of this gold were put together into a cube shape, each of its sides would measure 21.7 meters (71 ft).
The world's consumption of new gold produced is about 50% in jewelry, 40% in investments, and 10% in industry.
Gold's high malleability, ductility, resistance to corrosion and most other chemical reactions, as well as conductivity of electricity have led to its continued use in corrosion-resistant electrical connectors in all types of computerized devices (its chief industrial use).
Gold is also used in infrared shielding, the production of colored glass, gold leafing, and tooth restoration.
Auranofin is a gold-containing drug used to treat rheumatoid arthritis.
History
Gold was first discovered as shining, yellow nuggets.
“Gold is where you find it,” so the saying goes, and gold was first discovered in its natural state, in streams all over the world.
No doubt Gold was the first metal known to early hominids.
The first person or civilization to discover gold is the Ancient Egyptians.
They mined gold in Nubia around 2450 BC.
An Egyptian alchemist named Zosimos was the first to find pure gold (24 centuries before Columbus reached the Americas).
The discovery of gold is attributed to the ancient Egyptians, who made jewelry out of gold.
Gold was at a time when other metals were scarce and valuable.
Three thousand years ago, the Chinese discovered gold in the Yellow River.
The Chinese started trading for gold with other cultures, which led to the discovery of gold elsewhere in the world.
Tibetans discovered gold around 700 B.C.
They used Gold as a material for religious statues and jewelry.
GOLD Chemical Properties
Melting point: 1063 °C (lit.)
Boiling point: 2808 °C (lit.)
density: 19.3 g/mL at 25 °C (lit.)
refractive index: n20/589.3 1.523
Fp: 4 °C
storage temp.: 2-8°C
solubility H2O: soluble
form: wire
color: purple
Specific Gravity: 19.3
PH: 6-8
PH Range: 6 - 8
resistivity: 2.05 μΩ-cm, 0°C
Water Solubility: Soluble in hot sulfuric acid and aqua regia. Insoluble in water and acid.
Electrical Conductivity: 4.5× 107S/m
Thermal Conductivity: 320 W/(m·K)
λmax: 980 nm
Sensitive: Light Sensitive
Merck: 13,4529
Exposure limits NIOSH: IDLH 25 mg/m3
Stability: Stable. May react with halogens, strong oxidizing agents, ammonia, hydrogen peroxide. Reaction with ammonia or hydrogen peroxide may form explosive materials.
Cosmetics Ingredients Functions: COLORANT SKIN CONDITIONING - MISCELLANEOUS SLIP MODIFIER
SURFACE MODIFIER ANTIMICROBIAL
InChI: 1S/Au
InChIKey: PCHJSUWPFVWCPO-UHFFFAOYSA-N
Hardness, Vickers: 25
Modulus of Elasticity: 77.2 GPa, 60% Cold Worked
Poissons Ratio: 0.42
Shear Modulus: 27.2 GPa, 60% Cold Worked; Calculated Value
CAS DataBase Reference: 7440-57-5(CAS DataBase Reference)
EPA Substance Registry System: Gold (7440-57-5)
Absorption: 1 at 523nm
Chemical Properties
Gold does not have a distinctive odor at room temperature, but when heated it emits a sweet odor that is detected with difficulty.
Chloroauric acid composed of yellow-orange crystalline powder has a faint chlorine odor.
Physical properties
Gold is a soft, malleable, ductile, dense metal with a distinctive yellow color.
Gold is almost aheavy as lead, and both can be cut with a knife.
One ounce of gold can be beaten and poundedinto a thin sheet that is only a few molecules thick and that will cover over 300 square feetof surface.
Although gold is chemically nonreactive, it will react with chlorine and cyanidesolutions and can be dissolved in aqua regia.
Its melting point is 1,064.4°C, its boiling pointis 2,808°C, and its density is 19.3 g/cm3 (as compared to lead’s density of 11.35 g/cm3).
Characteristics
Gold is not only pleasing to look at but also pleasing to touch, which made it a desirablemetal for human decoration in prehistoric days.
Gold is still the preferred metal for jewelry makingtoday.
Gold is classed as a heavy, noble metal located just below copper and silver in group 11 ofthe periodic table.
Gold is a good conductor of electricity as well as an excellent heat reflectorof infrared radiation, which makes it an efficient thin coating on glass in skyscrapers to reflectthe heat of sunlight.
The purity of gold is measured in “carats” (one carat is equal to one part in twenty-four). Thepurest gold is rated at 24 carats, but it is much too soft to be used for jewelry.
Good jewelry ismade from 18-carat gold that is 18 parts gold and six parts alloy metal.
Thus, an 18-carat goldring is about 75% pure gold and contains about 25% of another metal, such as nickel or copper,to make it harder and more durable.
Other alloy metals mixed with gold are silver, platinum, andpalladium—all used to increase gold’s strength and reduce its cost.
Some less expensive jewelrycontains 14 or 10 carats of gold (14/24 or 10/24) as well as some other alloy metals.
Uses
In manufacture of jewelry; in gold plating other metals; as a standard of currency; most frequently alloyed with silver and copper.
For use in medicine, see Gold, Radioactive, Colloidal.
Gold has excellent properties as a reflecting mirror.
Gold black is utilized as the absorber of light by depositing on the plane of light incidence of a thermocouple.
Gold’s chemical and physical properties make it a very versatile element.
Gold's noncorrosivenature provides protection as plating for other metals.
Gold's malleability and ductile qualities meanit can be formed into many shapes, including very thin sheets (gold leaf) and very thin golddiode wires.
Gold has the ability to carry electricity with little resistance, making it an excellentcomponent for all kinds of electronic equipment.
Gold leaf finds many uses in surgery,space vehicles, and works of art.
Gold electronic switches do not create a dangerous spark whenengaged, and they last for a long time.
The element’s reflective surface provides protection frominfrared heat radiation as a coating on the visors of aerospace personnel, as well as on large windowexpanses in buildings.
Gold's color and durability make it a major metal for the jewelry industry.
Gold has been used to replace teeth for many ages, and the teeth usually last longer than theperson wearing them.
Gold is also the worldwide monetary standard, although the United Statesabandoned the gold standard in the 1930s.
Even so, gold is still traded as a commodity.
Smallamounts of other metals are added to gold coinage for hardening purposes so that the coins willnot wear out with use.
Gold bars (bullion) are stored in the treasuries of most countries.
Somecountries maintain huge stockpiles of gold for both monetary and industrial uses.
Two forms of gold provide medical treatments.
The radioactive isotope Au-198, with a shorthalf-life of 2.7 days, is used to treat cancer and is produced by subjecting pure gold to neutronswithin a nuclear reactor.
Among the first uses of gold are religious and cultural, as it became many decorations and idols for thousands of years.
The next major use of gold was as the first monetary systems, representing wealth and gradually replacing the barter system until the advent of modern economics.
Gold has found many industrial uses because of its excellent electrical and thermal conductivity properties.
Gold is used for plating other metals and as an alloying metal.
Gold is used in themanufacture of jewelry, dental inlays, art, currency, and electronic components, and in some medical devices to provide radio opacity.
Gold compounds have also found use in medicine in the treatment of certain cancers, rheumatoid arthritis, and discoid lupus (a rare skin disease), and in specialized surgical procedures.
Jewelry
Pure (24k) gold is often alloyed with other metals for use in jewelry, altering its hardness and ductility, melting point, color and other properties.
Alloys with lower karat rating, typically 22k, 18k, 14k or 10k, contain higher percentages of copper, silver, or other base metals in the alloy.
Nickel is toxic, and its release from nickel white gold is controlled by legislation in Europe.
Palladium-gold alloys are more expensive than those using nickel.
High-karat white gold alloys are more resistant to corrosion than are either pure silver or sterling silver, though not as corrosion-proof as platinum jewelry.
The Japanese craft of Mokume-gane exploits the color contrasts between laminated colored gold alloys to produce decorative wood-grain effects.
Gold solder is used for joining the components of gold jewelry by high-temperature hard soldering or brazing.
If the work is to be of hallmarking quality, the gold solder alloy must match the fineness of the work, and alloy formulas are manufactured to color-match yellow and white gold.
Gold solder is usually made in at least three melting-point ranges referred to as Easy, Medium and Hard.
By using the hard, high-melting point solder first, followed by solders with progressively lower melting points, goldsmiths can assemble complex items with several separate soldered joints. Gold can also be made into thread and used in embroidery.
Electronics
Only 10% of the world consumption of new gold produced goes to industry, but by far the most important industrial use for new gold is in fabrication of corrosion-free electrical connectors in computers and other electrical devices.
For example, according to the World Gold Council, a typical cell phone may contain 50 mg of gold, worth about three dollars.
But since nearly one billion cell phones are produced each year, a gold value of US$2.82 (equivalent to $3 in 2025) in each phone adds to US$2.82 billion in gold from just this application (equivalent to $3,102,513,077 in 2025).
Though gold is attacked by free chlorine, its good conductivity and general resistance to oxidation and corrosion in other environments (including resistance to non-chlorinated acids) has led to its widespread industrial use in the electronic era as a thin-layer coating on electrical connectors, thereby ensuring good connection.
For example, gold is used in the connectors of the more expensive electronics cables, such as audio, video and USB cables.
The benefit of using gold over other connector metals such as tin in these applications has been debated; gold connectors are often criticized by audio-visual experts as unnecessary for most consumers and seen as simply a marketing ploy.
However, the use of gold in other applications in electronic sliding contacts in highly humid or corrosive atmospheres, and in use for contacts with a very high failure cost (certain computers, communications equipment, spacecraft, jet aircraft engines) remains very common.
Pharmaceutical Applications
Gold has a long-standing tradition in medicine, as it has been used by many nations for thousands of years.
From as early as 2500 BC, Arabians, Chinese and Indians used gold compounds for medicinal purposes.
In mediaeval times, the elixir aurum potabile , whichwas an alcoholic mixture of herbs with some gold flakes, was sold by medicine men travelling around Europe and this elixir was supposed to cure most diseases.
In the nineteenth century, Na[AuCl4] was reported to treat syphilis, whilst others used it to cure alcoholism.
On a more serious note, Koch discovered in 1890 the antibacterial properties of gold cyanide.
In vitro experiments with the Mycobacterium tuberculosis showed that gold cyanide has the potential as a tuberculosis therapy.
Gold compounds were also investigated for the treatment of RA, when it was believed that RA was caused by bacteria, and many other health problems.
Production Methods
Gold has been known to mankind for more than 4000 years and since the times of the ancient Egyptian, Babylonian, Roman, Greek, and Chinese empires, gold has been recognized as the king of metals and an object of prestige and value.
Icons, objects of religious significance, coinage, jewelry, and funerary artifacts provide evidence of the goldsmith’s craft from early times.
During the Middle Ages, the demand for gold led the early alchemists to attempt converting base metals into gold.
Chinese alchemy was associated with Taoist philosophy that purported to transmute base metals into gold by use of a “medicine”; the gold produced was held to have amazing medicinal power to cure all diseases and to prolong life.
Early Egyptians and Greeks including Aristotle were masters of applied chemistry, although at the time it was closely linked with the embalming of bodies and religious rituals.
Much of the early chemistry of metals was shrouded in superstition, astrological speculations, and obscure symbolism.
Although transmutation of lead or iron to gold was thought possible in Arabic science up to 1000 A.D., the philosophy declined in the eleventh and twelfth centuries as more rational scientific ideas emerged and the true science of chemistry became established.
Gold was among the first metals to be mined.
Gold occurs naturally in its metallic form in many parts of the world and is distinctive by its lustrous appearance.
In its elementary state, gold is found admixed with quartz and pyrite in alluvial deposits in rivers and streams in the form of small scales or nuggets that were avidly sought in the days of the gold rushes as in California, Klondike (1890s), and Fraser Canyon (1850s).
Ores containing gold are quite rare and mostly comprise gold telluride (calaverite, krennerite— AuTe2) and complexes such as sylvanite, nagyagite, petzite, and krennerite with silver, antimony, and lead.
Gold possibly comprises no more than 0.004 ppm of the Earth’s crust but has a worldwide distribution with major deposits in South Africa, Siberia, China, South and North America, India, and Australia.
Recycling
In 1997, recycled gold accounted for approximately 20% of the 2700 tons of gold supplied to the market.
Jewelry companies such as Generation Collection and computer companies including Dell conduct recycling.
As of 2020, the amount of carbon dioxide CO2 produced in mining a kilogram of gold is 16 tonnes, while recycling a kilogram of gold produces 53 kilograms of CO2 equivalent.
Approximately 30 percent of the global gold supply is recycled and not mined as of 2020.
