Argon
Atomic Data
| Atomic Number | 18 |
| Symbol | Ar |
| Atomic Weight | 39.948 u |
| Density (STP) | 1.784 g/L |
| Melting Point | −189.35 °C (83.8 K) |
| Boiling Point | −185.85 °C (87.3 K) |
| Electronegativity | — |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 |
| Oxidation States | 0 |
| Phase at STP | Gas |
| Category | Noble Gas |
| Period / Group | 3 / 18 |
| CAS Number | 7440-37-1 |
Electron Configuration
[Ne] 3s2 3p6
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 6 | 18 |
| Total | 18 | 18 | ||
Abundance & Occurrence
Argon is present in Earth's crust at approximately 3.5 ppm by mass and at approximately 100 ppm by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Asphyxiation: Argon is a colourless, odourless inert gas denser than air; it can accumulate in low-lying confined spaces — pits, trenches, tanks — and displace oxygen, causing rapid unconsciousness and death without warning.
- Confined-space entry: Vessels and pipelines purged with argon must be verified to contain sufficient oxygen (>19.5%) before entry; continuous atmospheric monitoring and a standby rescue team are mandatory.
- Pressurised cylinders: Argon cylinders are stored under high pressure; cylinders must be secured, kept away from heat sources, and handled with regulators rated for the service pressure.
- Liquid argon: Liquid argon at −186 °C causes severe cryogenic burns on contact with skin or eyes; rapid vaporisation near the liquid can produce an immediately dangerous oxygen-deficient atmosphere.
Argon in the Real World
Real-World Uses
- Welding shield gas — Argon provides an inert atmosphere around the arc in TIG (GTAW) and MIG (GMAW) welding, preventing oxidation and nitrogen absorption in the molten weld pool of aluminium, stainless steel, and titanium.
- Incandescent and fluorescent lighting — Argon fills incandescent bulbs to suppress tungsten filament evaporation and is used in fluorescent lamps to maintain low-pressure discharge conditions.
- Semiconductor manufacturing — Argon plasma sputters thin metal films onto wafers in physical vapour deposition (PVD) and ion-milling processes, and purges furnace chambers during high-temperature diffusion steps.
- Wine preservation — Argon gas injected into opened wine bottles displaces oxygen and prevents oxidation, keeping wine fresh for weeks without the slightly different flavour profile that nitrogen can impart.
- Insulating double glazing — Argon-filled double-glazed window units reduce thermal conductance by approximately 30% compared with air-filled units, improving building energy efficiency.
- Cryogenic applications — Liquid argon (boiling point −186 °C) is used as a radiation detector medium in dark matter experiments and neutrino detectors, and as a cryogenic coolant in niche scientific applications.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
What is argon used for?
Argon is used as an inert shielding gas in TIG and MIG welding to prevent oxidation of the molten weld pool, in incandescent and fluorescent lighting as a fill gas, in semiconductor manufacturing to create inert atmospheres during crystal growth and plasma processing, in argon-filled double-glazed windows for thermal insulation, and in wine preservation to prevent oxidation after opening.
Is argon completely inert?
Argon is chemically inert under all ordinary conditions. It has no known stable neutral compounds at room temperature and pressure; its filled outer electron shell means it does not react with other elements or compounds. Under extreme conditions (high pressure or cryogenic temperatures), van der Waals complexes of argon with other atoms have been detected, and argon hydrofluoride (HArF) has been created at very low temperatures, but these are scientific curiosities rather than practical compounds.
How was argon discovered?
Argon was discovered in 1894 by Lord Rayleigh and Sir William Ramsay. Rayleigh noticed that nitrogen obtained from the atmosphere was consistently slightly denser than nitrogen produced chemically. Ramsay systematically removed all known components from air (oxygen, nitrogen, carbon dioxide, water vapour), and the residue — about 1% of the air volume — was a new, chemically unreactive gas they named argon, from the Greek word for 'lazy' or 'inactive'.
Why is argon used in light bulbs?
Incandescent light bulbs need an inert gas filling to prevent the hot tungsten filament from oxidising and burning through in air. Argon is used because it is cheap (it is the most abundant noble gas, making up about 0.93% of air), inert, and its relatively high molecular weight suppresses the evaporation and thermal diffusion of tungsten atoms from the filament, extending the life of the bulb. It replaced nitrogen as the standard fill gas in the early 20th century and is now being phased out along with incandescent bulbs.