Quick Facts
| Property | Value |
|---|---|
| Symbol | Ar |
| Atomic Number | 18 |
| Atomic Mass | 39.948 u |
| Category | Noble Gas |
| Period | 3 |
| Group | 18 |
| Block | p |
| Electron Configuration | [Ne] 3s² 3p⁶ |
Physical Properties
| Property | Value |
|---|---|
| State at 20°C | Gas |
| Density | 0.001784 g/cm³ |
| Melting Point | -189.34°C (83.81 K) |
| Boiling Point | -185.85°C (87.30 K) |
| Appearance | Colorless, odorless gas |
Atomic Properties
| Property | Value |
|---|---|
| Electron Configuration | [Ne] 3s² 3p⁶ |
| Electronegativity | N/A (no stable compounds) |
| First Ionization Energy | 1520.6 kJ/mol |
| Atomic Radius | 71 pm |
| Covalent Radius | 106 pm |
| Van der Waals Radius | 188 pm |
History and Discovery
Discovered by: Lord Rayleigh and William Ramsay Year of Discovery: 1894 Location: London, England
Etymology
The name "argon" comes from the Greek "argos" meaning "lazy" or "inactive," referring to its chemical inertness.
Discovery Story
Lord Rayleigh noticed in 1892 that nitrogen from air was slightly denser than nitrogen from chemical sources. In 1894, working with William Ramsay, they isolated a new gas from air that was chemically inert. Henry Cavendish had actually observed something similar in 1785 but didn't identify it as a new element. Ramsay and Rayleigh shared the 1904 Nobel Prizes (Chemistry and Physics, respectively) partly for this discovery.
Isotopes
| Isotope | Natural Abundance | Half-life | Decay Mode |
|---|---|---|---|
| ³⁶Ar | 0.334% | Stable | - |
| ³⁸Ar | 0.063% | Stable | - |
| ⁴⁰Ar | 99.60% | Stable | - |
| ³⁹Ar | Trace | 269 years | β⁻ |
Occurrence
Natural Abundance
Argon is the third most abundant gas in Earth's atmosphere (0.934% by volume), more abundant than carbon dioxide. Most atmospheric argon-40 was produced by radioactive decay of potassium-40 in rocks. Argon is the most abundant noble gas on Earth.
Extraction and Production
- Fractional Distillation of Air: Primary production method
- Byproduct: Produced during liquid oxygen and nitrogen manufacturing
- Sources: Atmospheric air
- Global production: about 700,000 tons annually
Applications and Uses
Welding and Metal Processing
- Shielding gas for TIG and MIG welding
- Inert atmosphere for titanium and other reactive metals
- Protecting molten metals from oxidation
Lighting
- Incandescent light bulb fill gas (prevents filament oxidation)
- Fluorescent tubes
- Discharge lamps
Scientific Applications
- Inert atmosphere for sensitive experiments
- Argon-40/argon-39 dating of rocks
- Cryogenic preservation
- Spectroscopy carrier gas
Other Uses
- Thermal insulation in double-glazed windows
- Electronics manufacturing (clean room atmospheres)
- Winemaking (prevents oxidation)
- 3D printing (atmosphere control)
Biological Role
Argon has no known biological role. It is chemically inert and does not participate in any biochemical reactions.
In the Human Body
Argon is not metabolized or used by the body. It is breathed in and out unchanged.
Medical Uses
Argon plasma coagulation is used in some surgical procedures. It has been studied for neuroprotection.
Safety and Hazards
Toxicity
Argon is non-toxic but can act as a simple asphyxiant by displacing oxygen in enclosed spaces.
Handling Precautions
- Can displace oxygen in confined spaces causing asphyxiation
- Compressed gas cylinders require proper handling
- Liquid argon can cause frostbite
- No fire hazard—completely inert
Environmental Impact
Argon is environmentally benign. It does not contribute to ozone depletion or climate change and is naturally abundant in the atmosphere.
Interesting Facts
- Argon is the cheapest noble gas because it is so abundant in the atmosphere
- Argon-40 is produced by decay of potassium-40, allowing potassium-argon dating of rocks
- Despite being called "lazy," argon has formed compounds under extreme conditions (argon fluorohydride)
- About 1% of the air you breathe is argon
- Argon's density makes it effective for thermal insulation—it's about 67% denser than air