Argon
Argon (Ar) is element 18, a noble gas in group 18, period 3, with an atomic mass of 39.95 u. It is a gas at room temperature and boils at −185.85 °C. Its electron configuration is [Ne] 3s² 3p⁶.
Argon is a colorless, odorless noble gas that makes up almost one percent of the air around us, far more than any other noble gas. It's chemically inert under virtually all ordinary conditions, which is exactly why it's prized wherever a reactive atmosphere would cause problems.
- Group · Period
- 18 · 3
- At room temp
- gas
- Melts at
- 83.8 K
- Density
- 1.7837 g/L
- Discovered
- 1894
Key facts about argon
Quick answers, built from the sourced data in the property tables.
- What is the electron configuration of argon?
- The electron configuration of argon is [Ne] 3s² 3p⁶. Written out in full, that is 1s² 2s² 2p⁶ 3s² 3p⁶.
- What is the density of argon?
- Argon is a gas, so its density is usually given in grams per litre: 1.7837 g/L at STP (0 °C and 1 atm), which is 0.0017837 g/cm³.
- What are the melting and boiling points of argon?
- Argon melts at 83.8 K (−189.35 °C, −308.83 °F) and boils at 87.3 K (−185.85 °C, −302.53 °F).
- How many stable isotopes does argon have?
- Argon has 3 stable isotopes: Ar-36 (0.3336%), Ar-38 (0.0629%), and Ar-40 (99.6035%). Percentages are natural abundances.
Uses
Argon’s chemical unreactivity makes it useful anywhere a process needs to avoid oxygen or nitrogen interfering. Welders rely on it heavily as a shielding gas, flooding the weld area so hot metal doesn’t react with the surrounding air. It also fills the gap between panes in energy-efficient double- and triple-glazed windows, where its low thermal conductivity helps insulate buildings. Incandescent and fluorescent light bulbs are often filled with argon to protect their filaments or electrodes from oxidizing.
Argon also plays a role in preservation: museums and wineries sometimes use it to displace oxygen around sensitive documents, artifacts, or opened bottles, slowing down oxidation and decay without introducing any chemical reactivity of its own.
History
Argon was discovered in 1894 by English physicist Lord Rayleigh and Scottish chemist William Ramsay, who noticed a small but persistent discrepancy: nitrogen gas isolated from air was slightly denser than nitrogen produced by breaking down nitrogen compounds. Investigating that gap led them to isolate a new gas that resisted every attempt to make it react. They named it argon, from the Greek for “idle,” and its discovery opened the door to identifying the rest of the noble gases in the years that followed.
Fun facts
- Argon is the third most abundant gas in Earth's atmosphere, after nitrogen and oxygen, making up about 0.93% of the air by volume.
- It was the first noble gas ever discovered, identified in 1894 — the whole noble gas group was essentially unknown before it.
- Argon's name comes from the Greek word 'argos,' meaning idle or lazy, a nod to how reluctant it is to react with anything.
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Frequently asked questions
Why is argon used in light bulbs?
Incandescent bulbs use a hot tungsten filament that would quickly oxidize and burn out if exposed to air. Filling the bulb with argon instead of air creates an inert atmosphere that lets the filament get extremely hot without reacting, extending the bulb's life considerably.
How was argon hiding from chemists for so long?
Because it barely reacts with anything, argon doesn't show up in compounds the way most elements do, so there was no chemical trail leading to it. It was only found because Lord Rayleigh noticed that nitrogen extracted from air was slightly denser than nitrogen made from chemical compounds — the tiny difference turned out to be argon mixed in.
Is argon dangerous to breathe?
Argon itself isn't toxic, but it is dangerous in a different way: it's heavier than air and can displace oxygen in an enclosed space without any smell or warning sign, creating a risk of asphyxiation. That's why spaces using large volumes of argon, like welding bays, need good ventilation.
Isotopes
24 known isotopes
Swipe to see all columns →
| Isotope | Natural abundance | Half-life | Decay mode | Mass excess | Binding energy / nucleon | Decay width | Spin/parity | Magnetic moment | Quadrupole moment |
|---|---|---|---|---|---|---|---|---|---|
| Ar-36 stable | 0.3336% | Stable | — | -30,231.54 keV | 8,519.91 keV | — | 0+ | 1 μN | 0.11 b |
| Ar-38 stable | 0.0629% | Stable | — | -34,714.83 keV | 8,614.28 keV | — | 0+ | 0.48 μN | — |
| Ar-40 stable | 99.6035% | Stable | — | -35,039.9 keV | 8,595.26 keV | — | 0+ | -0.04 μN | 0.01 b |
| Ar-30 | — | 10 ps | Two-proton emission (100%) | 22,071 keV | 6,866 keV | 4.56 × 10-5 eV | 0+ | — | — |
| Ar-31 | — | 15.0 ms | Electron capture / beta-plus decay (100%), Beta-plus, proton emission (68.3%), B+2P (8.9%) | 11,325 keV | 7,252 keV | 3.04 × 10-14 eV | 5/2+ | — | — |
| Ar-32 | — | 98 ms | Electron capture / beta-plus decay (100%), ECP (35.58%) | -2,200.35 keV | 7,700.01 keV | 4.66 × 10-15 eV | 0+ | — | — |
| Ar-33 | — | 173.0 ms | Electron capture / beta-plus decay (100%), ECP (38.7%) | -9,384.3 keV | 7,928.96 keV | 2.64 × 10-15 eV | 1/2+ | -0.723 μN | — |
| Ar-34 | — | 843.8 ms | Electron capture / beta-plus decay (100%) | -18,378.29 keV | 8,197.67 keV | 5.41 × 10-16 eV | 0+ | — | — |
| Ar-35 | — | 1.7756 s | Electron capture / beta-plus decay (100%) | -23,047.29 keV | 8,327.46 keV | 2.57 × 10-16 eV | 3/2+ | 0.632 μN | -0.084 b |
| Ar-37 | — | 35.011 d | Electron capture (100%) | -30,947.68 keV | 8,527.14 keV | 1.51 × 10-22 eV | 3/2+ | 1.146 μN | 0.076 b |
| Ar-39 | — | 268 Y | Beta-minus decay (100%) | -33,242.2 keV | 8,562.6 keV | 5.39 × 10-26 eV | 7/2- | -1.59 μN | -0.116 b |
| Ar-41 | — | 109.61 m | Beta-minus decay (100%) | -33,067.51 keV | 8,534.37 keV | 6.94 × 10-20 eV | 7/2- | -1.31 μN | -0.042 b |
| Ar-42 | — | 32.9 Y | Beta-minus decay (100%) | -34,422.68 keV | 8,555.61 keV | 4.39 × 10-25 eV | 0+ | — | — |
| Ar-43 | — | 5.37 m | Beta-minus decay (100%) | -32,009.81 keV | 8,488.24 keV | 1.42 × 10-18 eV | 5/2(-) | -1.022 μN | 0.142 b |
| Ar-44 | — | 11.87 m | Beta-minus decay (100%) | -32,673.26 keV | 8,493.84 keV | 6.41 × 10-19 eV | 0+ | — | — |
| Ar-45 | — | 21.48 s | Beta-minus decay (100%) | -29,770.8 keV | 8,419.95 keV | 2.12 × 10-17 eV | 5/2- 7/2- | — | — |
| Ar-46 | — | 8.4 s | Beta-minus decay (100%) | -29,771.26 keV | 8,412.38 keV | 5.43 × 10-17 eV | 0+ | — | — |
| Ar-47 | — | 1.23 s | Beta-minus decay (100%), Beta-minus, neutron emission (0.2%) | -25,367.27 keV | 8,311.43 keV | 3.71 × 10-16 eV | (3/2)- | — | — |
| Ar-48 | — | 416 ms | Beta-minus decay (100%), Beta-minus, neutron emission (38%) | -22,354.93 keV | 8,243.67 keV | 1.10 × 10-15 eV | 0+ | — | — |
| Ar-49 | — | 170 ms | Beta-minus decay (100%), Beta-minus, neutron emission (65%) | -17,060 keV | 8,132 keV | 2.68 × 10-15 eV | — | — | — |
| Ar-50 | — | 106 ms | Beta-minus decay (100%), Beta-minus, neutron emission (37%), B-2N | -13,230 keV | 8,054 keV | 4.30 × 10-15 eV | 0+ | — | — |
| Ar-51 | — | — | Beta-minus decay (100%) | -6,490 keV | 7,922 keV | — | — | — | — |
| Ar-52 | — | — | Beta-minus decay (100%), B-2N, B-3N | -1,380 keV | 7,827 keV | — | 0+ | — | — |
| Ar-53 | — | 620 ns | B-2N, Beta-minus, neutron emission, Beta-minus decay | 6,791 keV | 7,677 keV | 7.36 × 10-10 eV | — | — | — |
Spin/parity describes the nucleus's intrinsic angular momentum and symmetry. Magnetic moment (in nuclear magnetons, μN) and quadrupole moment (in barns, b) describe the shape of the nucleus's charge distribution — a nonzero quadrupole moment means the nucleus isn't perfectly spherical. These are only measured for a subset of isotopes, mostly stable or long-lived ones, so many rows show "—" rather than a value.