Gold

Gold is the chemical element with atomic number 79 and the symbol Au. It is a soft, yellow metal that is chemically unreactive, dissolving only in a special acid mixture. Gold has been used for jewelry, coins and ornament since prehistoric times, and it is now also important in electronics, dentistry and chemical manufacturing.

History of gold

Gold has been known since prehistoric times and was one of the first metals to be worked, mainly because it could be found as nuggets or as particles in the beds of streams. Such was the demand that by 2000 BC the Egyptians had begun mining it. The death mask of Tutankhamen, who died in 1323 BC, contained 100 kilograms of the metal, and the royal graves of ancient Ur, in modern Iraq, which flourished from 3800 to 2000 BC, also held gold objects.

The minting of gold coins began around 640 BC in the Kingdom of Lydia, in what is now Turkey. The first coins used electrum, a natural alloy of gold and silver, and the first pure gold coins were minted in the reign of King Croesus, who ruled from 561 to 547 BC.

Gold also shaped early chemistry. The Royal Society of Chemistry notes that early alchemists were obsessed with gold and pursued the aim of transmuting base metals, usually lead, into it. The traditional alchemical symbol for gold also served as a sun symbol, and much of the mythology around the metal relates to the sun. PubChem lists the discovery date as ancient, because no individual discoverer is known.

Properties of gold

PubChem, drawing on IUPAC data, gives gold a standard atomic weight of 196.96657. Its electron configuration is [Xe] 6s1 4f14 5d10. Gold sits in group 11 and period 6 of the periodic table and is a transition metal. Its common oxidation states are +3 and +1, which are the charges gold atoms usually carry when they form compounds.

Gold is a dense solid with a density of 19.282 grams per cubic centimeter, more than 19 times that of water. It melts at 1337.33 kelvin, about 1064 degrees Celsius, and boils at 3129 kelvin, about 2856 degrees Celsius. The Royal Society of Chemistry describes it as a soft metal with a characteristic yellow color.

Gold has an electronegativity of 2.54 on the Pauling scale, a relative measure of how strongly an atom attracts electrons. Its first ionization energy, the energy needed to remove one electron from a neutral atom, is 9.226 electronvolts, or about 890 kilojoules per mole. The electron affinity, the energy released when an atom gains an electron, is 2.309 electronvolts.

Gold is chemically unreactive, although it will dissolve in aqua regia, a mixture of nitric and hydrochloric acids. This unreactive character explains why gold is found as the metal itself and why gold surfaces stay clean in conditions that would spoil most other metals.

Occurrence and production of gold

Gold is one of the few elements to occur in a natural state, meaning as the free metal and not combined with other elements. It is found in veins and in alluvial deposits, which are sediments left by flowing water. Because early people could simply pick up nuggets and stream particles, gold was in use long before the techniques of smelting were developed.

The oceans also hold gold. Seawater contains about 4 grams of gold in 1,000,000 tonnes of water. Overall that is a huge amount of gold, but because the concentration is so low, the Royal Society of Chemistry notes that attempts to reclaim it have always failed.

Uses of gold

Most mined gold is stored as bullion, meaning bars or ingots held as a store of value. Gold is also used extensively in jewelry, either in its pure form or as an alloy. The term carat indicates the amount of gold present in an alloy. Twenty-four carat gold is pure but very soft, so 18-carat and 9-carat alloys are commonly used because they are more durable.

Gold is used for coinage and has served as the standard for the monetary systems of some countries. It can be beaten into very thin sheets called gold leaf, which are used in art, for decoration and as architectural ornament.

Electroplating, a process that uses an electric current to deposit a thin metal coating, can cover another metal with a very thin layer of gold. It is used for gears in watches, artificial limb joints, cheap jewelry and electrical connectors. Gold is ideal for protecting electrical copper components because it conducts electricity well and does not corrode, which would break the contact. Thin gold wires are used inside computer chips to join circuits.

Dentists sometimes use gold alloys in fillings, and a gold compound is used to treat some cases of arthritis. Gold nanoparticles are increasingly used as industrial catalysts. Vinyl acetate, which is used to make PVA for glue, paint and resin, is made with a gold catalyst.

Isotopes of gold

Gold has a single naturally occurring isotope, gold-197, which makes up 100 percent of natural gold. An isotope is a form of an element whose atoms have the same number of protons but different numbers of neutrons. Gold is therefore called a monoisotopic element, and its atomic weight is simply set by the mass of gold-197.

The Royal Society of Chemistry also lists gold-198, a radioactive isotope that decays by beta emission with a half-life of 2.695 days. It does not occur naturally in measurable amounts and is made artificially.

Health and environmental effects of gold

The Royal Society of Chemistry states that gold has no known biological role and is non-toxic. The gold compound used for some cases of arthritis is a medicine directed by clinicians, and it is a separate matter from the metal itself.

The unreactive character of gold means it stays in the environment as the metal. This entry gives general background drawn from reference sources and is not advice.

Editorially reviewed by Specialty Digest Editorial TeamLast reviewed November 4, 2026Researched and drafted with AI assistanceReport an issue