Name: Gold
Symbol: Au
Atomic Number: 79
AtomicWeight: 196.966550
Family: Transition metals
CAS RN: 7440-57-5
Description: The most malleable and ductile metal
State (25C): Solid
Oxidation states: +1, +3

Molar Volume: 10.2 cm3/mole
Valence Electrons: 5d106s1

Boiling Point:  3080K, 2807C, 5085F
Melting Point:
1337.73K, 1064.58C, 1948.24F
Electrons Energy Level: 2, 8, 18, 32, 18, 1
Isotopes: 36 + 1 Stable
Heat of Vaporization: 334.4 kJ/mol
Heat of Fusion: 12.55 kJ/mol
Density: 19.32 g/cm3 @ 300K
Specific Heat: 0.128 J/gK
Atomic Radius: 1.79
Ionic Radius: 0.85
Electronegativity: 2.54 (Pauling); 1.42 (Allrod Rochow)
Vapor Pressure: 0.000237 Pa @ 1064.58C

1s2 2s2p6 3s2p6d10 4s2p6d10f14 5s2p6d10 6s1


Gold has been known and highly valued since prehistoric times.  It may have been the first metal used by humans and was valued for ornamentation and rituals.   Egyptian hieroglyphs from as early as 2600 BC describe gold, which king Tushratta of the Mitanni claimed was "more plentiful than dirt" in Egypt.  Egypt and Nubia had the resources to make them major gold-producing areas for much of history.   Gold is also mentioned several times in the Old Testament, and is included with the gifts of the magi in the first chapters of Matthew New Testament.  The south-east corner of the Black Sea was famed for its gold.  Exploitation is said to date from the time of Midas, and this gold was important in the establishment of what is probably the world's earliest coinage in Lydia between 643 and 630 BC.

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Alchemical Symbols, Aurum

The European exploration of the Americas was fueled in no small part by reports of the gold ornaments displayed in great profusion by Native American peoples, especially in Central America, Peru, and Colombia.

Gold has long been considered one of the most precious metals, and its value has been used as the standard for many currencies (known as the gold standard) in history.   Gold has been used as a symbol for purity, value, royalty, and particularly roles that combine these properties.  Gold as a sign of wealth and prestige was made fun of by Thomas More in his treatise Utopia.  On that imaginary island, gold is so abundant that it is used to make chains for slaves, tableware and lavatory-seats. When ambassadors from other countries arrive, dressed in ostentatious gold jewels and badges, the Utopians mistake them for menial servants, paying homage instead to the most modestly-dressed of their party.

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Additional Representations of Alchemical Symbols for Gold

There is an age-old tradition of biting gold in order to test its authenticity.   Although this is certainly not a professional way of examining gold, the bite test should score the gold because gold is considered a soft metal according to the Moh's scale of mineral hardness.  The purer the gold the easier it should be to mark.   Painted lead can cheat this test because lead is softer than gold (and may invite a small risk of lead poisoning if sufficient lead is absorbed by the biting).

Gold in antiquity was relatively easy to obtain geologically; however, 75% of all gold ever produced has been extracted since 1910.  It has been estimated that all the gold in the world that has ever been refined would form a single cube 20 m (66 ft) on a side (8000 m).

The primary goal of the alchemists was to produce gold from other substances, such as lead — presumably by the interaction with a mythical substance called the philosopher's stone.  Although they never succeeded in this attempt, the alchemists promoted an interest in what can be done with substances, and this laid a foundation for today's chemistry.  Their symbol for gold was the circle with a point at its center, which was also the astrological symbol, the Egyptian hieroglyph and the ancient Chinese character for the Sun.

During the 19th century, gold rushes occurred whenever large gold deposits were discovered.  The first major gold strike in the United States occurred in a small north Georgia town called Dahlonega.  Further gold rushes occurred in California; Colorado; Otago, Australia: Black Hills, South Dakota; and Klondike, Alaska.

Because of its historically high value, much of the gold mined throughout history is still in circulation in one form or another.


Gold has been associated with the extremities of utmost evil and great sanctity throughout history.  In the Book of Exodus, the Golden Calf is a symbol of idolatry and rebellion against God.  In Communist propaganda, the golden pocket watch and its fastening golden chain were the characteristic accessories of the class enemy, the bourgeois and the industrial tycoons.  Credit card companies associate their product with wealth by naming and colouring their top-of-the-range cards “gold;” although, in an attempt to out-do each other, platinum and the even-more-elite black card) has now overtaken gold.

On the other hand in the Book of Genesis, Abraham was said to be rich in gold and silver, and Moses was instructed to cover the Mercy Seat of the Ark of the Covenant with pure gold.  Eminent orators such as John Chrysostom were said to have a “mouth of gold with a silver tongue.”  Gold is associated with notable anniversaries, particularly in a 50-year cycle, such as a golden wedding anniversary, golden jubilee, etc.

Great human achievements are frequently rewarded with gold, in the form of medals and decorations.  Winners of races and prizes are usually awarded the gold medal (such as the Olympic Games and the Nobel Prize), while many award statues are depicted in gold (such as the Academy Awards, the Golden Globe Awards, the Emmy Awards, the Palme d'Ore, and the British Academy Film Awards.

Medieval kings were inaugurated under the signs of sacred oil and a golden crown, the latter symbolizing the eternal shining light of heaven and thus a Christian king's divinely inspired authority.  Wedding rings are traditionally made of gold; since it is long-lasting and unaffected by the passage of time, it is considered a suitable material for everyday wear as well as a metaphor for the relationship.  In Orthodox Christianity, the wedded couple is adorned with a golden crown during the ceremony, an amalgamation of symbolic rites.

The symbolic value of gold varies greatly around the world, even within geographic regions.  For example, gold is quite common in Turkey but considered a most valuable gift in Sicily.

From most ancient times, gold has been connected to religion and spirituality, especially associated with the Sun.  It was also seen as the best material to decorate religious imagery, all over history.


Chemically, gold is a trivalent and univalent transition metal.  Gold does not react with most chemicals, but is attacked by chlorine, fluorine, aqua regia and cyanide.   Gold dissolves in mercury, forming amalgam alloys.  In particular, gold is insoluble in nitric acid, which will dissolve most other metals.  Nitric acid has long been used to confirm the presence of gold in items, and this is the origin of the colloquial term "acid test," referring to a gold standard test for genuine value.

2s2 2p6
3s2 3p6 3d10
4s2 4p6 4d10 4f14
5s2 5p6 5d10

Gold is a metallic element with a characteristic yellow color, but can also be black or ruby when finely divided, while colloidal solutions are intensely colored and often purple.  These colors are the result of gold's plasmon frequency lying in the visible range, which causes red and green light to be reflected, and blue light to be absorbed.   Only silver colloids exhibit the same interactions with light, albeit at a shorter frequency, making silver colloids yellow in color.

It is a dense, soft, shiny, yellow metal, and is the most malleable and ductile of the known metals.  A single gram can be beaten into a sheet of one square meter, or an ounce into 300 square feet.  Gold readily forms alloys with many other metals.  These alloys can be produced to increase the hardness or to create exotic colors.  Adding copper yields a redder metal, iron blue, aluminum purple, platinum white, and natural bismuth and silver alloys produce black.  Native gold contains usually eight to ten percent silver, but often much more — alloys with a silver content over 20% are called electrum.  As the amount of silver increases, the color becomes whiter and the specific gravity becomes lower.  It is usually found in conjunction with silver, quartz (SiO2), calcite (CaCO3), lead, tellurium, zinc or copper.  There is roughly 1 milligram of gold dissolved in every ton of seawater, although extracting it currently costs more than the gold is worth.

Gold is a good conductor of heat and electricity, and is not affected by air and most reagents.  Heat, moisture, oxygen, and most corrosive agents have very little chemical effect on gold, making it well-suited for use in coins and jewelry; conversely, halogens will chemically alter gold, and aqua regia dissolves it by virtue of the elemental chlorine generated by this acid mixture.

Common oxidation states of gold include +1 (gold (I) or aurous compounds) and +3 (gold (III) or auric compounds).  Gold ions in solution are readily reduced and precipitated out as gold metal by adding any other metal as the reducing agent.  The added metal is oxidized and dissolves allowing the gold to be displaced from solution and be recovered as a solid precipitate.

Recent research undertaken by Sir Frank Reith of the Australian National University shows that microbes play an important role in forming gold deposits, transporting and precipitating gold to form grains and nuggets that collect in alluvial deposits.

High quality pure metallic gold is tasteless, in keeping with its resistance to corrosion (it is metal ions which confer taste to metals).

In addition, gold is extremely heavy, with a cubic foot thereof weighing in at upwards of 1200 pounds (around 19300 kgm-1


The metal occurs as nuggets or grains in rocks, underground "veins" and in alluvial deposits.  Since the 1880s, South Africa has been the source for a large proportion of the world’s gold supply.  Production in 1970 accounted for 79% of the world supply, producing about 1,000 tons.  However, production in 2004 was 342 tons. This decline was due to the increasing difficulty of extraction and changing economic factors affecting the industry in South Africa.

The city of Johannesburg was built atop the world's greatest gold finds.  Gold fields in the Free State and Gauteng provinces are deep and require the world's deepest mines.  The Second Boer War of 1899-1901 between the British Empire and the Afrikaner Boers was at least partly over the rights of miners and possession of the gold wealth in South Africa.

Other major producers are Canada, United States and Australia.  Mines in South Dakota and Nevada supply two-thirds of gold used in the United States.  Siberian regions of Russia also used to be significant in the global gold mining industry.   Kolar Gold Fields in India is another example of a city being built on the greatest gold deposits in India.  In South America, the controversial project Pascua Lama aims at exploitation of rich fields in the high mountains of Atacama Desert, at the border between Chile and Argentina.  Today about one-quarter of the world gold output is estimated to originate from artisanal or small scale mining.

After initial production, gold is often subsequently refined industrially by the Wohlwill process or the Miller process.  Other methods of assaying and purifying smaller amounts of gold include parting and inquartation as well as cuppelation, or refining methods based on the dissolution of gold in aqua regia.


Pure gold is too soft for ordinary use and is typically hardened by alloying with silver, copper, or other metals.  In various countries, gold, and its many alloys, are most often used in jewelry, coinage and as a standard for monetary exchange.   When sold in the form of jewelry, gold is measured in carats (k), with pure gold being designated as 24k.  It is, however, more commonly sold in lower measurements of 22k, 18k, 14k and 10k.  A lower "k" indicates that a higher percent of copper or silver in the alloy, with copper being the more commonly used metal.   Fourteen carat gold-copper alloy is nearly identical in color to certain bronze alloys, and both may be used to produce police and other badges.  Eighteen carat gold, with a high copper content, is found in some antique jewelry and has a distinct, though not dominant, copper cast, creating an attractively warm color.  A similar carat weight, when alloyed with silvery metals, appears less warm in color.  Some low carat white metal alloys are sold as "white gold" and are silver in appearance, but have a sightly more yellow cast.  They are far more resistant to corrosion than are either pure silver or sterling silver.

Carat weights of twenty and higher are more common in modern jewelry.  Gold coins intended for circulation prior to the 1930s were typically 22k, for hardness. Modern collector/investment bullion coins (which do not require good mechanical wear properties) are typically 24k, although the American Gold Eagle continues to be made at 22k.   Currently, the Canadian Gold Maple Leaf coin contains the highest purity gold of any popular bullion coin, at 99.99% (.9999 fine).

Other Uses:

Chlorauric acid (HAuCl4) is used to preserve photographs by replacing the silver atoms present in an image.


Economic gold extraction can be achieved from ore grades as little as 0.5 g/1000 kg (0.5 ppm) on average in large easily mined deposits.  Typical ore grades in open-pit mines are 1–5 g/1000 kg (1-5 ppm), ore grades in underground or hard rock mines are usually at least 3 g/1000 kg (3 ppm) on average.  Since ore grades of 30 g/1000 kg (30 ppm) are usually needed before gold is visible to the naked eye, in most gold mines the gold is invisible.

The world's oceans hold a vast amount of gold, but in very low concentrations (perhaps 1-2 parts per billion).  A number of people have claimed to be able to economically recover gold from sea water, but so far they have all been either mistaken or crooks.   Reverend Prescott Jernegan ran a gold-from seawater swindle in America in the 1890s.  A British fraud ran the same scam in England in the early 1900s.

Fritz Haber (the German inventor of the Haber process) attempted commercial extraction of gold from sea water in an effort to help pay Germany's reparations following the First World War.  Unfortunately, his assessment of the concentration of gold in sea water was unduly high, probably due to sample contamination.  The effort produced little gold and cost the German government far more than the commercial value of the gold recovered.  No commercially viable mechanism for performing gold extraction from sea water has yet been identified.  Gold synthesis is not economically viable and is unlikely to become so in the foreseeable future.

The average gold mining and extraction costs are $238 per troy ounce but these can vary widely depending on mining type and ore quality.  In 2001, global mine production amounted to 2,604 tons, or 67% of total gold demand in that year.  At the end of 2001, it was estimated that all the gold ever mined totalled 145,000 tons.


Gold forms the basis for a monetary standard used by the International Monetary Fund (IMF) and the Bank of Settlements (BIS).  Its ISO currency code is XAU.

Like other precious metals, gold is measured by troy weight and by grams.  When it is alloyed with other metals the term carat or karat is used to indicate the amount of gold present, with 24 karats being pure gold and lower ratings proportionally less. The purity of a gold bar can also be expressed as a decimal figure ranging from 0 to 1, known as the millesimal fineness, such as 0.995 being very pure.

The price of gold is determined on the open market, but a procedure known as the Gold Fixing in London, originating in september 1919, provides a daily benchmark figure to the industry.  The afternoon fixing appeared in 1968 to fix a price when US markets are open.

The high price of gold is due to its rare amount.  Only three parts out of every billion in the Earth's crust is gold.

Historically gold was used to back currency; in an economic system known as the gold standard, a certain weight of gold was given the name of a unit of currency.  For a long period, the United States government set the value of the US dollar so that one troy ounce was equal to $20.67 ($664.56/kg), but in 1934 the dollar was revalued to $35.00 per troy ounce ($1125.27/kg).  By 1961 it was becoming hard to maintain this price, and a pool of US and European banks agreed to manipulate the market to prevent further currency devaluation against increased gold demand.

On March 17, 1968, economic circumstances caused the collapse of the gold pool, and a two-tiered pricing scheme was established whereby gold was still used to settle international accounts at the old $35.00 per troy ounce ($1.13/g) but the price of gold on the private market was allowed to fluctuate; this two-tiered pricing system was abandoned in 1975 when the price of gold was left to find its free-market level.  Central banks still hold historical gold reserves as a store of value although the level has generally been declining.  The largest gold depository in the world is that of the U.S. Federal Reserve Bank in New York, which holds about 3% of the gold ever mined, as does the similarly-laden U.S. Bullion Depository at Fort Knox.

Since 1968 the price of gold on the open market has ranged widely, with a record high of $850/oz ($27,300/kg) on January 21, 1980, to a low of $252.90/oz ($8,131/kg) on June 21, 1999 (London Fixing).  On May 11, 2006 the London gold fixing was $715.50/oz ($23,006/kg).

In 2005 the World Gold Council estimated total global gold supply to be 3,859 tons and demand to be 3,754 tons, giving a surplus of 105 tons.


Although gold is a noble metal, it forms many and diverse compounds.  The oxidation state of gold in its compound ranges from -1 to +5 but Au (I) and Au (III) dominate.  Gold (I), referred to as the aurous ion, is the most common oxidation state with “soft” ligands such as thioethers, thiolates, and tertiary phosphines.  Au (I) compounds are typically linear.  A good example is Au(CN)2, which is the soluble form of gold encountered in mining.  Curiously, aurous complexes of water are rare. The binary gold halides, such as AuCl, form zig-zag polymeric chains, again featuring linear coordination at Au.  Most drugs based on gold are Au (I) derivatives.

Gold (III) (“auric”) is a common oxidation state and is illustrated by gold (III) chloride, AuCl3.  Its derivative is chloroauric acid, HAuCl4, which forms when Au dissolves in aqua regia.  Au (III) complexes, like other d8 compounds, are typically square planar.

Less Common Oxidation States: Au (-I), Au (II), and Au (V)

Compounds containing the Au- anion are called aurides.  Cesium auride, CsAu which crystallizes in the cesium chloride motif.  Other aurides include those of Rb+, K+, and tetramethylammonium (CH3)4N+.   Gold (II) compounds are usually diamagnetic with Au-Au bonds such as [Au(CH2)2P(C6H5)2]2Cl2.   A noteworthy, legitimate Au (II) complex contains xenon as a ligand, [AuXe4](Sb2F11)2.   Gold pentafluoride is the sole example of Au (V), the highest verified oxidation state.

Some gold compounds exhibit , which describes the tendency of gold ions to interact at distances that are too long to be a conventional Au-Au bond but shorter that van der Waals bonding.  The interaction is estimated to be comparable in strength to that of a hydrogen bond.

Mixed Valence Compounds

Well-defined cluster compounds are numerous.  In such cases, gold has a fractional oxidation state.  A representative example is the octahedral species {Au(P(C6H5)3)}6+2.   Gold chalcogenides, e.g. "AuS" feature equal amounts of Au (I) and Au (III).


There is one stable isotope of gold, and 18 radioisotopes with 195Au being the most stable with a half-life of 186 days.

Gold has been proposed as a "salting" material for nuclear weapons (cobalt is another, better-known salting material).  A jacket of natural gold, irradiated by the intense high-energy neutron flux from an exploding thermonuclear weapon, would transmute into the radioactive isotope Au-198 with a half-life of 2.697 days and produce approximately .411 MeV of gamma radiation, significantly increasing the radioactivity of the weapon's fallout for several days.  Such a weapon is not known to have ever been built, tested, or used.

The isotope gold-198, (half-life: 2.7 days) is used in some cancer treatments and for treating other diseases.

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Atomic Mass
169Au 168.99808 ~150 s
170Au 169.99612 310 s
171Au 170.991879 30 s
172Au 171.99004 4.7 ms
173Au 172.986237 25 ms
174Au 173.98476 139 ms
175Au 174.98127 ~100 ms
176Au 175.98010 1.08 seconds
177Au 176.976865 1462 ms
178Au 177.97603 2.6 seconds
179Au 178.973213 7.1 seconds
180Au 179.972521 8.1 seconds
181Au 180.970079 13.7 seconds
182Au 181.969618 15.5 seconds
183Au 182.967593 42.8 seconds
184Au 183.967452 20.6 seconds
185Au 184.965789 4.25 minutes
186Au 185.965953 10.7 minutes
187Au 186.964568 8.4 minutes
188Au 187.965324 8.84 minutes
189Au 188.963948 28.7 minutes
190Au 189.964700 42.8 minutes
191Au 190.96370 3.18 hours
192Au 191.964813 4.94 hours
193Au 192.964150 17.65 hours
194Au 193.965365 38.02 hours
195Au 194.9650346 186.098 days
196Au 195.966570 6.1669 days
197Au 196.9665687 Stable
198Au 197.9682423 2.69517 days
199Au 198.9687652 3.139 days
200Au 199.97073 48.4 minutes
201Au 200.971657 26 minutes
202Au 201.97381 28.8 seconds
203Au 202.975155 53 seconds
204Au 203.97772 39.8 seconds
205Au 204.97987 31 seconds

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Gold Data

Atomic Structure

  • Atomic Radius: 1.79
  • Atomic Volume: 10.2cm3/mol
  • Covalent Radius: 1.34
  • Cross Section (Thermal Neutron Capture) Barns: 98.7
  • Crystal Structure: Cubic face centered
  • Electron Configuration:
    1s2 2s2p6 3s2p6d10 4s2p6d10f14 5s2p6d10 6s1
  • Electrons per Energy Level: 2, 8, 18, 32, 18, 1
  • Ionic Radius: 0.85
  • Filling Orbital: 5d10
  • Number of Electrons (with no charge): 79
  • Number of Neutrons (most common/stable nuclide): 118
  • Number of Protons: 79
  • Oxidation States: 1, 3
  • Valence Electrons: 5d10 6s1

Chemical Properties

  • Electrochemical Equivalent: 2.4496 g/amp-hr
  • Electron Work Function: 5.1eV
  • Electronegativity: 2.54 (Pauling); 1.42 (Allrod Rochow)
  • Heat of Fusion: 12.55 kJ/mol
  • Incompatibilities:
  • Ionization Potential
    • First: 9.225
    • Second: 20.521
  • Valence Electron Potential (-eV): 51

Physical Properties

  • Atomic Mass Average: 196.9665
  • Boiling Point: 3080K, 2807C, 5085F
  • Coefficient of Lineal Thermal Expansion/K-1: 14.16E-6
  • Conductivity
    Electrical: 0.452 106/cm
    Thermal: 3.17 W/cmK
  • Density: 19.32 g/cm3 @ 300K
  • Description:
    Soft bright yellow transition metal.
  • Elastic Modulus:
    • Bulk: 171/GPa
    • Rigidity: 26/GPa
    • Youngs: 78.5/GPa
  • Enthalpy of Atomization: 364 kJ/mole @ 25C
  • Enthalpy of Fusion: 12.55 kJ/mole
  • Enthalpy of Vaporization: 324.4 kJ/mole
  • Flammablity Class:
  • Freezing Point: see melting point
  • Hardness Scale
    • Brinell: 2450 MN m-2
    • Mohs: 2.5
    • Vickers: 216 MN m-2
  • Heat of Vaporization: 334.4 kJ/mol
  • Melting Point: 1337.73K, 1064.58C, 1948.24F
  • Molar Volume: 10.2 cm3/mole
  • Optical Reflectivity: 95%
  • Physical State (at 20C & 1atm): Solid
  • Specific Heat: 0.128 J/gK
  • Vapor Pressure: 0.000237 Pa @ 1064.58C

Regulatory / Health

  • CAS Number
    • 7440-57-5
  • OSHA Permissible Exposure Limit (PEL)
    • No limits set by OSHA
  • OSHA PEL Vacated 1989
    • No limits set by OSHA
  • NIOSH Recommended Exposure Limit (REL)
    • No limits set by NIOSH
  • Levels In Humans:
    Note: this data represents naturally occuring levels of elements in the typical human, it DOES NOT represent recommended daily allowances.
    • Blood/mg dm-3: (0.1-4.2)E-4
    • Bone/p.p.m: 0.016
    • Liver/p.p.m: 0.0004
    • Muscle/p.p.m: n/a
    • Daily Dietary Intake: n/a
    • Total Mass In Avg. 70kg human: 0.2 mg
  • Discovery Year: Unknown
  • Name Origin:
    Gold from old English word geolo (yellow) Au from Latin: aurum (gold).
  • Abundance:
    • Earth's Crust/p.p.m.: 0.0011
    • Seawater/p.p.m.: 0.00001
    • Atmosphere/p.p.m.: N/A
    • Sun (Relative to H=1E12): 5.6
  • Sources:
    Found in quartz veins in in extrusive rocks, with copper ore and native metals. Around 1,400 tons are produced each year world wide. Primary mining areas are South Africa, USA, Canada and Russia.
  • Uses:
    Very malleable. Used in electronics, jewelry dental crowns and coins. Supposedly around half of the world's supply of gold is stored in the United States Treasury Department's gold depository in Fort Knox Kentucky, which is considered to be one of the most secure buildings in the world.
  • Additional Notes:
    Gold is poorly absorbed by the body. Gold-based anti-arthritics can cause liver and/or kidney damage.

Ionization Energy (eV): 9.226 eV
Estimated Crustal Abundance: 410-3 milligrams per kilogram
Estimated Oceanic Abundance:
410-6 milligrams per liter

Transition Metals
Group 3
10 (VIIIB) 11
Period 4 21
Period 5 39
Period 6 57
Period 7 89