What is argon?
Element 18: the “lazy” gas that makes up almost one per cent of the air
Looking for Google’s AI model? Gemini 4 Argon is explained here.
Argon is a chemical element with the symbol Ar and atomic number 18: a colourless, odourless, non-toxic noble gas that makes up 0.934% of Earth’s atmosphere. Its name comes from the Greek for “lazy”, because it almost never reacts with anything. That is exactly why industry uses it: to shield welds, fill light bulbs and keep oxygen away from things it would spoil.
Almost one per cent of every breath you take is argon. It passes in and out of your lungs untouched, because argon reacts with almost nothing. That stubbornness made it the first noble gas ever discovered, and it is the reason welders, lighting makers, winemakers and the keepers of America’s founding documents all depend on it.
- Symbol
- Ar (it was “A” until 1957)
- Atomic number
- 18
- Group
- 18, the noble gases
- Share of Earth’s air
- 0.934% by volume, the third most abundant gas
- Boiling point
- 87.3 K (about −186 °C)
- Discovered
- 1894, by Lord Rayleigh and William Ramsay
- Main isotope on Earth
- Argon-40, 99.6%
- World production
- About 700,000 tonnes a year
- Food additive code
- E938
What kind of element is argon?
Argon sits in group 18 of the periodic table with the other noble gases. Its outer shell of electrons is full, with a complete set of eight, which makes it stable and extremely resistant to bonding with other elements. As a gas, a liquid or a solid it is colourless, odourless, non-flammable and non-toxic.
It is also surprisingly common. Argon is the third most abundant gas in Earth’s atmosphere, at 0.934% by volume: more than twice as abundant as water vapour and 23 times as abundant as carbon dioxide. Its triple point, 83.8058 kelvin, is one of the fixed points that define the International Temperature Scale of 1990.
Why is it called argon?
The name comes from the Ancient Greek argos, meaning “lazy” or “inactive”, a reference to how rarely the element takes part in chemical reactions. Its symbol was “A” until 1957, when the International Union of Pure and Applied Chemistry changed it to “Ar”.
Who discovered argon?
Henry Cavendish suspected in 1785 that air contained an unreactive gas. More than a century later, Lord Rayleigh noticed that nitrogen made from chemical compounds was 0.5% lighter than nitrogen taken from the air. The difference was tiny, but he and William Ramsay concluded that another gas was hiding in the atmospheric nitrogen.
In 1894, at University College London, they isolated it by removing oxygen, carbon dioxide, water and nitrogen from a sample of clean air, partly by repeating an experiment of Cavendish’s that used an electric arc. What was left was a gas that would not react, the first noble gas to be discovered. Two other researchers, H. F. Newall and W. N. Hartley, had independently seen unexplained lines in the spectrum of air in 1882.
Where does argon come from?
Nearly all the argon in Earth’s atmosphere is argon-40, produced by the radioactive decay of potassium-40 in the planet’s crust. In the wider universe the most common form is argon-36, made in supernovas. Argon is also found in the atmospheres of Mars, Mercury and Saturn’s largest moon, Titan.
Because Earth’s argon is mostly the heavy argon-40, its atomic weight is greater than that of potassium, the next element. That puzzled chemists at first, since Dmitri Mendeleev had arranged his periodic table by atomic weight; the order was later explained by Henry Moseley’s work.
Industry gets argon from the air. Liquefied air is separated by cryogenic fractional distillation, which works because its parts boil at different temperatures: nitrogen at 77.3 K, argon at 87.3 K and oxygen at 90.2 K. About 700,000 tonnes of argon are produced worldwide each year.
What is argon used for?
Most argon is used where something hot must be kept away from oxygen and nitrogen. It is the shielding gas in common kinds of arc welding, it protects titanium and other reactive metals while they are processed, and it surrounds the silicon and germanium crystals grown for electronics. Other noble gases would work for most of these jobs, but argon is by far the cheapest, because it is a by-product of making liquid oxygen and nitrogen.
It fills incandescent light bulbs, where it stops the hot filament oxidising, and argon discharge lamps glow lilac or violet, or blue with a little mercury added. Argon also insulates energy-efficient double-glazed windows and inflates the dry suits of technical divers, since it is inert and conducts heat poorly.
It is a preservative. Argon displaces oxygen in food packaging, where it carries the code E938; winemakers use it to keep oxygen off the surface of wine; and since 2002 the U.S. National Archives has kept the Declaration of Independence and the Constitution in argon-filled cases, replacing helium, which leaked out of the containers. In medicine, liquid argon freezes and destroys tumours in cryoablation, and blue argon lasers are used to weld arteries and correct eye defects.
Scientists use it too. Liquid argon is the target in experiments hunting for dark matter and neutrinos, and geologists date rocks by measuring the argon that radioactive potassium leaves behind, using potassium–argon and argon–argon dating.
Can argon form compounds?
Barely. Before 1962 all the noble gases were thought to be unable to form compounds at all. Heavier noble gases have since been made to react, and chemists have created argon fluorohydride (HArF), but it is only stable below 17 K, about −256 °C. Argon forms no confirmed stable compounds at room temperature.
Is argon dangerous?
Argon is not poisonous, but it can kill. It is 38% denser than air, so in an enclosed space it collects low down and pushes out the oxygen, and because it has no colour, smell or taste nobody notices. In 1994 a man in Alaska died after entering an argon-filled section of oil pipe under construction.
Athletes have abused it to simulate the low-oxygen conditions of altitude training. In 2014 the World Anti-Doping Agency added argon and xenon to its list of prohibited substances and methods, although at the time there was no reliable test for it.
Argon and Google’s Gemini 4
Since 30 September 2026, “argon” has had a second meaning. Google gave the name Argon to the first model in its Gemini 4 generation of artificial intelligence. The AI has nothing to do with the element; our Gemini 4 explainer covers what it is.
Timeline
- 1785Henry Cavendish suspects air contains an unreactive gas.
- 1882Newall and Hartley see unexplained lines in the spectrum of air.
- 1894Lord Rayleigh and William Ramsay isolate argon at University College London.
- 1957The symbol changes from A to Ar.
- 2002The U.S. National Archives seals its founding documents in argon.
- 2014The World Anti-Doping Agency bans argon as a doping method.
Sources
- Wikipedia: Argon, characteristics, history, occurrence, isotopes, compounds, production, applications and safety.
Quotes are as reported in these sources. Found a mistake, or something out of date? Write to info@wikidrift.com.
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