Periodic table › Argon
1. Identity and classification
Colorless, odorless, tasteless monatomic gas; emits characteristic vivid glow in high-voltage plasma tubes
- Name and symbol
- Argon (Argon) · Ar
- Atomic number
- 18
- Relative atomic weight / mass number
- 39.95 ± 0.16
- Group · period · block
- 18 · 3 · p
- Category
- Noble Gas
- State near room temperature
- Gas
- Stable isotopes
- At least one stable isotope
- CAS number
- 7440-37-1
Square brackets [A] indicate a representative isotope mass number, not an average atomic weight. Neutron counts differ between isotopes.
2. Atomic structure and electron configuration
- Protons · electrons in a neutral atom
- 18 · 18
- Neutrons in reference isotope
- 22 (40Ar)
- Full electron configuration
1s² 2s² 2p⁶ 3s² 3p⁶- Abbreviated configuration
[Ne]3s² 3p⁶- Electrons per shell
- 2, 8, 8
- Listed oxidation states
- 0
- Electronegativity
- Not established
- First ionization energy
- 1520.609 kJ/mol · 15.76 eV
- Electron affinity
- Not established
- Covalent radius
- 106 pm
- van der Waals radius
- 188 pm
Configurations of superheavy elements may include theoretical predictions. Different definitions of atomic radius are not interchangeable.
3. Physical and thermal properties
- Density
- 0.0017837 g/cm³
- Melting point
- 83.8 K · -189.35 °C · -308.83 °F
- Boiling point
- 87.3 K · -185.85 °C · -302.53 °F
- Crystal structure
- FCC
- Specific heat
- 0.52 J/(g·K)
- Thermal conductivity
- 0.01772 W/(m·K)
- Enthalpy of fusion
- 1.18 kJ/mol
- Enthalpy of vaporization
- 6.43 kJ/mol
- Magnetic ordering
- Diamagnetic
- Mohs hardness
- Not established
- Speed of sound
- 323 m/s
Density and structure depend on temperature, pressure and allotrope. 25°C is a room-temperature reference, not STP. Unestablished values are not zero.
4. Chemical behavior and compounds
Closed valence shells explain low reactivity; xenon and krypton can form compounds under suitable conditions.
Selected compounds: Monatomic gas — no stable compounds at STP
Reaction reference
No ordinary reaction with air.
No ordinary reaction with water.
5. Isotopes
| Isotope | Status | Natural abundance | Half-life |
|---|---|---|---|
| 36Ar | Stable | 0.3336% | Stable |
| 38Ar | Stable | 0.0629% | Stable |
| 40Ar | Stable | 99.6035% | Stable |
| 41Ar | Radioactive | — | 109.61 m |
Half-life units: s seconds, m minutes, h hours, d days, Y years. A dash means no natural-abundance value is given, not zero. Listed records are selected ground states; metastable states are distinct.
6. Discovery and occurrence
- Discovery
- 1894 CE
- Scientists associated with discovery
- Lord Rayleigh & William Ramsay
- Location
- United Kingdom
- Origin
- Natural
- Listed crustal abundance
- Not established
Minerals and naming reference
Fractional distillation of liquid air (0.934% of atmosphere)
Named from scientific/historical roots associated with Argon (Ar), discovered or characterized by Lord Rayleigh & William Ramsay.
7. Applications
Inert shielding gas in TIG/MIG welding, incandescent & fluorescent light bulbs, double-glazed insulated windows
Detailed applications by field
- everyday
- Inert shielding gas in TIG/MIG welding, incandescent & fluorescent light bulbs, double-glazed insulated windows
- industry
- Used in noble gas processing, specialized alloys, and chemical manufacturing (Inert shielding gas in TIG/MIG welding, incandescent & fluorescent light bulbs, double-glazed insulated windows).
- electronics
- Applied in electronic components, semiconductors, or functional coatings where Argon's electronic structure ([Ne] 3s² 3p⁶) provides target conductivity.
- medicine
- Diagnostic imaging, biomedical instrumentation, or pharmaceutical synthesis research.
- energy
- Utilized in power generation, battery materials, catalysts, or nuclear technology involving Argon.
- aerospace
- High-performance materials, structural alloys, or space instrumentation utilizing Argon.
- agriculture
- Soil geochemistry analysis, trace micronutrient research, or analytical environmental monitoring.
- science
- Spectroscopic standard, crystallography, and quantum chemistry studies of Period 3 p-block elements.
8. Biological role and safety
Hazard depends on the isotope, chemical form, dose and exposure route.
Elemental substances, ions, compounds and radioisotopes can have different health effects. This is an educational reference; laboratory work requires the material safety data sheet and trained supervision.
Biological role reference
Classified as non-essential in human and biological systems.