Gold

This article is about the metal. For the color, see Gold (color).

Gold, ₇₉Au

Gold
Appearance	Metallic yellow
Standard atomic weight Ar°(Au)
	196.966570(4)
Gold in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson Ag ↑ Au ↓ Rg platinum ← gold → mercury
Atomic number (Z)	79
Group	group 11
Period	period 6
Block	d-block
Electron configuration	[Xe] 4f14 5d10 6s1
Electrons per shell	2, 8, 18, 32, 18, 1
Physical properties
Phase at STP	solid
Melting point	1337.33 K ​(1064.18 °C, ​1947.52 °F)
Boiling point	3243 K ​(2970 °C, ​5378 °F)
Density (near r.t.)	19.3 g/cm3
when liquid (at m.p.)	17.31 g/cm3
Heat of fusion	12.55 kJ/mol
Heat of vaporization	342 kJ/mol
Molar heat capacity	25.418 J/(mol·K)
Vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 1646 1814 2021 2281 2620 3078
Atomic properties
Oxidation states	−3, −2, −1, 0, +1, +2, +3, +5 (an amphoteric oxide)
Electronegativity	Pauling scale: 2.54
Ionization energies	1st: 890.1 kJ/mol 2nd: 1980 kJ/mol
Atomic radius	empirical: 144 pm
Covalent radius	136±6 pm
Van der Waals radius	166 pm
Spectral lines of gold
Other properties
Natural occurrence	primordial
Crystal structure	​face-centered cubic (fcc)
Speed of sound thin rod	2030 m/s (at r.t.)
Thermal expansion	14.2 µm/(m⋅K) (at 25 °C)
Thermal conductivity	318 W/(m⋅K)
Electrical resistivity	22.14 nΩ⋅m (at 20 °C)
Magnetic ordering	diamagnetic
Molar magnetic susceptibility	−28.0×10−6 cm3/mol (at 296 K)
Tensile strength	120 MPa
Young's modulus	79 GPa
Shear modulus	27 GPa
Bulk modulus	180 GPa
Poisson ratio	0.4
Mohs hardness	2.5
Vickers hardness	188–216 MPa
Brinell hardness	188–245 MPa
CAS Number	7440-57-5
History
Naming	from Latin aurum, meaning gold
Discovery	In the Middle East (before 6000 BCE)
Symbol	"Au": from Latin aurum
Isotopes of gold
Main isotopes Decay abun­dance half-life (t1/2) mode pro­duct 195Au synth 186.01 d ε 195Pt 196Au synth 6.165 d β+ 196Pt β− 196Hg 197Au 100% stable 198Au synth 2.69464 d β− 198Hg 199Au synth 3.139 d β− 199Hg

Gold is a soft, dense, bright yellow metal. It is a chemical element. Its chemical symbol is Au. Its atomic number is 79. As a precious metal, it has been used for many thousands of years by people all over the world, for jewelry, and as money. It is easy to shape. This means, it can be hammered into sheets or stretched into wires without breaking. Chemically, gold is a noble metal. This means it barely reacts with anything. Only platinum is less reactive.

Gold is tough. It does not dissolve in most acids. But, if you mix nitric acid and hydrochloric acid together, a combo called aqua regia, gold will dissolve. When it does, it forms a solution called tetrachloroaurate, which is just gold floating in a liquid in a special way. Interestingly, nitric acid alone cannot dissolve gold, even though it will dissolve metals like silver. That is why people long ago could test for real gold using acid—it became known as the “acid test.” Gold can also dissolve in cyanide solutions, which is how miners extract it from rocks. It can also mix with mercury, forming something called an amalgam. In the mercury case, gold does not really react, it just mixes in like sugar dissolving in water.

Gold is important because it is rare, but also easier to use than other rare metals. It is also used to repair and replace teeth and in electronic equipment such as computers. Even some medicines like auranofin, has gold, and is used to treat arthritis. It has been used for coins, jewelry, and art.

For a long time, money was tied to gold through the gold standard, though that ended in 1971. The color of this metal is also called gold. Gold is so valued that the discovery of a new place to mine has sometimes caused a gold rush. The deepest workplaces for miners in the world are in South African gold mines 4 km (2.5 miles) down.

Often, gold is found as a native metal. This means it is not part of an ore, lying around in nature, as nuggets or tiny grains in rocks, or riverbeds. It could be mixed with other metals like silver (called electrum), copper, or even platinum. Sometimes it is trapped inside minerals like pyrite or combined with tellurium in rare compounds. Most of the gold on Earth is deep inside the Earth's core because it is dense, sinking there. Nearly all discovered gold was brought to the surface by meteorites.

In 2023, China produced the most gold, followed by Russia and Australia. As of 2020, a total of around 201,296 tonnes of gold exist above ground. All the gold ever mined could fit in a cube about 21.7 meters (71 ft) on each side. Around half of new gold goes to jewelry, 40% to investments, and 10% to industry.

Properties

In chemistry, gold is chemical element 79, a transition metal in Group 11. It has an atomic weight of 199.966 a.m.u. Its symbol is Au, from the Latin word for gold, aurum. It is a "noble metal" meaning it has low chemical reactivity. It will, however, react with aqua regia (a mixture of nitric and hydrochloric acid) to form chloroauric acid. Gold has only one stable isotope, ¹⁹⁷Au. All other isotopes are radioactive and do not occur naturally. Most of them decay to mercury, platinum, or iridium.

Gold is very soft. It is malleable, meaning a goldsmith can hammer it into thin metal sheets. It is also ductile, which means it can be pulled into wire. When it is used in money or in jewelry, it is often alloyed with copper, silver, or both to make it harder.

Most metals are gray in color. Gold is yellow because of the way its electrons behave. The only other metal in common use that has a non-gray color is copper. Caesium also has a gold-like color, but it is not commonly used as a metal because it reacts with water.

Gold is a fairly good electrical conductor, better than aluminium, but not as good as copper or silver. Copper and brass electrical connectors, especially those used with computer and audio/video equipment, are often plated with gold for corrosion resistance. Connectors that are intended for soldering are not made of gold because it makes the solder joint brittle. Gold is also a good heat conductor, although it is not commonly used for this purpose due to its cost.

Nancy Johnson and her Olympic gold medal

Origins

Gold is made in space. Scientists have found three main ways gold is made in space:

• Supernova explosions
• Neutron stars smashing together
• Flares from magnetars, like solar flares

All three involve a process called the r-process, which makes elements heavier than iron. For a long time, people thought supernovae made most of the gold. But then in 2017, scientists saw two neutron stars smash into each other (event GW170817). They realized these collisions actually produce tons of gold, maybe most of it in the universe. Those two neutron stars smashing into each other produced, between 3 and 13 Earth masses of gold.

But neutron stars smashing into each other are rare and happen late in the universe (approximately once every 100,000 years), so they cannot explain why very old stars already have gold. That is where magnetar flares come in. These flares happened earlier and more often, sprinkling gold across the galaxy. In fact, magnetars might make 1–10% of all the heavy elements in the Milky Way.

Language and culture

A gold medal is often the given to the first-place winner in a race or other sports.

The most important international currencies of the 19th century used the gold standard.

Something that is in some way good may be given gold status.

Gold can mean that something or someone is very good or has done very well.

Safety

Gold is one of the safest elements to handle, but the chemicals used to process it can be dangerous. Metallic gold is non-toxic, which is unusual for a heavy metal. Soluble gold compounds, however, are toxic to the liver and kidneys. Gold is non-flammable, even in a pure oxygen environment or when finely powdered. It does not react with most household or laboratory chemicals. Gold is commonly processed with cyanide, which is highly toxic. Most of the cyanide is destroyed in the production process, so it is not present in the final product, but it can be a hazard to workers in a gold processing plant. Illegally mined gold is often processed with, and contaminated with mercury. Since gold conducts electricity, gold jewelry should never be worn when working with electricity.

Mining

In 2022, China mined [c. 10% or] "10.6 percent [330 tons] of global share"; Russia and Australia (each) mined 320 tons of gold.

Other information

In 2025, gold was traded

• under USD 2,800 for a troy ounce, but also
• [above $4,320 or at c.] 4,326

A troy ounce, is equal to 31.1034768 grams.

Related pages

• Alchemy
• Gold coin

Other websites

• Atomic Properties Archived 2011-02-21 at the Wayback Machine
• Gold Institute
• Gold -Citizendium