Atomic number 79

Gold

Au
+ phase
− phase

Shells Orbitals 4f 5d 6s

Drag to rotate; pinch or Ctrl + scroll to zoom. Arrow keys rotate, + − zoom, R resets.

79 electrons in 6 shells: 2, 8, 18, 32, 18, 1.

Shells are a teaching model: an electron does not travel on a ring at a fixed distance.

Category: Transition metal
Period: 6
Group: 11
Block: d
Standard atomic weight: 196.97(1) Da
Electron configuration: [Xe] 4f¹⁴ 5d¹⁰ 6s¹
Phase at 25 °C: solid
Melting point: 1064.18 °C
Boiling point: 2970 °C
Density: 19.282 g/cm³
Electronegativity (Pauling): 2.54
Discovered: Prehistoric times, as the free metal

Neighbours in the table

Pt Hg

In shorthand gold is [Xe] 4f¹⁴ 5d¹⁰ 6s¹, which spells out as 79 electrons in six shells of 2, 8, 18, 32, 18 and 1. It closes the third run of the d block, the series from lanthanum to gold that adds ten d electrons to the fifth shell. That leaves the 5d subshell full and a single 6s electron outside it.

Copper, at the top of the same group, shows the same s¹ d¹⁰ arrangement, which OpenStax puts down to the extra stability of a filled subshell; gold follows copper’s pattern. With every d orbital filled, the textbook adds, gold is not technically a transition element, though the name is used for the whole block. A d-block atom forming a positive ion gives up the s electron first, then d electrons. PubChem lists +1 and +3 as gold’s oxidation states; an oxidation state is the bookkeeping charge an atom would carry if all its bonds were ionic.

In a lump the metal is yellow; finely divided it can look black, ruby or purple, Los Alamos notes. Los Alamos ranks it the most malleable and ductile of all metals: one ounce hammers out into 300 square feet of sheet. Pure gold is soft, so it is usually alloyed for strength. Air and most reagents leave it untouched.

Where it is found

Gold, like silver and copper, turns up in the ground as the element itself. OpenStax gives the reason: these metals react so little that they survive in deposits as nuggets, whereas iron occurs almost only oxidised, as rust. Los Alamos finds native gold very widely distributed, almost always in company with quartz or pyrite, or else in tellurides, its compounds with tellurium.

The metal lies in veins and in alluvial deposits, the gravel a river lays down, and is won by mining and panning. Nuggets a pan could catch; fine dust gave trouble, so prospectors added mercury, which gathered the gold into an amalgam, an alloy with mercury, for easier collection. The mercury lost over the years left many California streams polluted, and its toxicity has since cut amalgam use sharply.

The US Geological Survey puts 2024 world mine output at 3,300 metric tons. China led, then Russia, Australia, Canada and the United States; together they produced 41%. Nevada mined about 70% of the American 160 tons and Alaska about 16%. Ore is worked by cyaniding, dissolving gold in cyanide solution, amalgamating and smelting, then often refined by electrolysis.

Why it matters

The US Geological Survey’s 2024 breakdown of world consumption gives jewellery 45%, central banks and similar institutions 21%, bars 19% and coins and medals 7%. Electrical and electronic goods took 6%. The average price in 2024, 2,400 dollars a troy ounce, about 31 g, was the highest for any year on record, 23% above 2023.

Gold conducts heat and electricity well and does not tarnish in air, so it goes into electrical connectors and printed circuit boards. OpenStax puts it in electrochemical terms: gold has a high reduction potential, meaning it resists being oxidised, which suits it to circuits and jewellery alike. Gold also reflects infrared strongly and is inert, so it coats some satellites and keeps the sun’s heat off spacecraft and skyscrapers. Gold-coated mirrors go into telescopes built for infrared light.

Gold melts, and freezes again, at 1064.18 °C. For many years thermometry’s international scales, ITS-27 and ITS-48, used the freezing point of gold as a fixed calibration point; the 1968 revision, IPTS-68, reassigned its value. Chlorauric acid, HAuCl₄, tones and preserves photographs by taking the place of the silver atoms in the image. Gold-198 is used against cancer, and a seed of it can be left in place rather than removed, because its half-life is short, 2.7 days.

Properties

Properties of gold Standard atomic weights from IUPAC/CIAAW (abridged, 2024); other values from PubChem's periodic table, kelvin converted to °C.
Property	Value	Unit	Source
Atomic number	79
Standard atomic weight	196.97(1) Da	Da	IUPAC/CIAAW 2024
Melting point	1064.18 °C	°C	Los Alamos: 1064.18 °C
Boiling point	2970 °C	°C	Los Alamos: 2970 °C
Density	19.282 g/cm³	g/cm³
Electronegativity (Pauling)	2.54
Electron configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s¹ 4f¹⁴ 5d¹⁰
Phase at 25 °C	solid

Safety

Gold metal in its everyday forms, a ring, a coin, a sheet of leaf or a plated contact, is harmless. PubChem’s record for elemental gold, CID 23985, carries no hazard classification under the GHS labelling system; 502 of 506 company reports find that it meets no hazard criteria. The record’s one workplace note is allergic contact dermatitis reported among electroplaters, dental technicians, jewellers and others; the same entry restricts the skin-sensitisation danger to soluble gold compounds. Anyone working with it has the Laboratory Chemical Safety Summary to consult.

Questions

Why doesn't gold rust or tarnish?

Its resistance to oxidation is the textbook answer. OpenStax notes that on heating, oxygen reacts with every transition metal except palladium, platinum, silver and gold; the oxides of those four can be made by other routes but break down when heated. The same chapter ties this to gold's high reduction potential, a measure of how strongly it resists being oxidised. Los Alamos sums the metal up as unaffected by air and most reagents.

What does 18 karat gold mean?

Karat counts the parts of pure gold in twenty-four. An 18 karat ring is 18 parts gold to 6 parts other metal, and 24 karat is the pure element. Pure gold is soft, and Jefferson Lab's note in PubChem's record lists silver, copper, platinum and palladium as the metals added for strength. Gold alloys go into jewellery, dental fillings and coins, and jewellery took 45% of world gold consumption in the US Geological Survey's 2024 estimate.

Is there gold in seawater?

Yes, a trace. Los Alamos gives 0.1 to 2 milligrams of gold in a ton of seawater, depending on where the sample is taken, and reports that no method has yet been found to recover it at a profit. Jefferson Lab's note in PubChem's record says extracting the gold would cost more than it is worth. The crust is not rich either: PubChem's record puts it at four thousandths of a milligram per kilogram.

Can anything dissolve gold?

Yes, though not much. Gold is generally unreactive, but a mixture of nitric and hydrochloric acids takes it into solution as chlorauric acid. The mixture was named aqua regia, royal water, because it dissolved the king of metals, and OpenStax explains its reach: it handles gold, platinum and other metals that are harder to oxidise than hydrogen. Nitric acid alone dissolves silver and leaves gold untouched, which is how gold was once separated from silver.

How much gold has ever been mined?

Jefferson Lab's note in PubChem's record estimates that all the gold ever refined would fit in a cube 20 metres on a side; Los Alamos gives the same picture as a cube 60 feet on a side. The US Geological Survey puts world reserves at 64,000 metric tons. Old metal keeps coming back: 90 tons of scrap were recycled in the United States in 2024, about 45% of reported consumption.