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About Argon

Argon Bohr

After nitrogen and oxygen, argon is the third most plentiful gas (9,300 ppm) in Earth’s atmosphere. Like other noble gases, argon is produced through fractional distillation of liquefied air. Its use in industrial applications and consumer products necessitates the production of roughly 700,000 tons of argon, yearly. Because of its inert nature and its plentiful availability when compared to other noble gases, it is widely used in lighting applications – both incandescent and fluorescent – to prevent oxygen from corroding the bulb’s filament.

Expanding on such properties, argon is also used in many industrial applications which require an atmospheric barrier (shielding gas) between a high-temperature source and the normal composition of air. The most common examples of such shielding are argon’s use in arc welding and graphite electric furnaces. More exotic applications include the scientific community’s liquefaction of argon to observe neutrinos and search for dark matter. Argon’s eclectic and inert nature also lends itself to be used as a preservative (of food and historical documents alike), a humane asphyxiation method for the culling of diseased animals, a method to extinguish fires, and when used in a laser apparatus, has a host of medical uses ranging from correcting eye defects to welding arteries.

Argon was the first noble gas discovered. By removing oxygen, carbon dioxide and all moisture from an air sample in 1894, Sir William Ramsay of England and Lord Rayleigh of Scotland found that the resulting nitrogen was heavier than the nitrogen produced from reducing chemical compounds. This led the duo to believe that there was another element within the resulting nitrogen sample. After several months and after successfully isolating nitrogen from the other components of air, argon was discovered. English scientist Henry Cavendish, studying the same isolation of elements in air 200 years earlier, had concluded that elements other than nitrogen and oxygen must be present; Cavendish, however, did not have the means to isolate these elements. For the duo’s discovery and Rayleigh’s persistence, Rayleigh went on to win the Nobel Prize in Physics in 1904.

Argon is a stable and largely inert element that has yet to produce any known compound at room temperature, and only one compound (HArF) at very low temperatures. This compound does not have any practical application outside of fundamental scientific research. Three isotopes of argon are naturally occurring: 36Ar, 38Ar, and 40Ar with 40Ar being the most abundant on Earth, by far. 40Ar is produced through the slow decay of 40K in rocks at the Earth’s crust over long periods of time. The relative abundance of these three isotopes inverts in the atmospheres of outer planets within the solar system, where the production of argon is dominated by stellar nucleosynthesis and the decomposition of rocks is naturally far less abundant.

Argon Properties

Argon Bohr ModelArgon is a Block P, Group 18, Period 3 element. The number of electrons in each of Argon's shells is 2, 8, 8 and its electronic configuration is [Ne] 3s2 3p6. In its elemental form argon's CAS number is 7440-37-1. The argon atom has a covalent radius of 106± and its Van der Waals radius is Air is the primary raw material used to produce argon products. Argon constitutes 1.28% by mass and 0.934% by volume of the Earth's atmosphere. Argon was discovered and first isolated by Lord Raleigh and Sir William Ramsay in 1894. Argon was the first noble gas to be discovered.

Argon information, including technical data, properties, and other useful facts are specified below. Scientific facts such as the atomic structure, ionization energy, abundance on Earth, conductivity and thermal properties are included.

Symbol: Ar
Atomic Number: 18
Atomic Weight: 39.95
Element Category: noble gases
Group, Period, Block: 18, 3, p
Color: colorless
Other Names: Argo, Argônio
Melting Point: -189.36  °C, -308.848  °F, 83.79 K
Boiling Point: -185.85  °C, -302.53  °F, 87.3 K
Density: 1656 (40 K) kg·m3
Liquid Density @ Melting Point: 1.40 g/cm3
Density @ 20°C: 0.001784 g/cm3
Density of Solid: 1616 kg·m3
Specific Heat: N/A
Superconductivity Temperature: N/A
Triple Point: 83.8058 K, 68.89 kPa
Critical Point: 150.687 K, 4.863 MPa
Heat of Fusion (kJ·mol-1): 1.21
Heat of Vaporization (kJ·mol-1): 6.53
Heat of Atomization (kJ·mol-1): 0
Thermal Conductivity: 17.72x10-3  W·m-1·K-1
Thermal Expansion: N/A
Electrical Resistivity: N/A
Tensile Strength: N/A
Molar Heat Capacity: 5R/2 = 20.786 (Cp) J·mol-1·K-1
Young's Modulus: N/A
Shear Modulus: N/A
Bulk Modulus: N/A
Poisson Ratio: N/A
Mohs Hardness: N/A
Vickers Hardness: N/A
Brinell Hardness: N/A
Speed of Sound: (gas, 27 °C) 323 m·s-1
Pauling Electronegativity: N/A
Sanderson Electronegativity: 3.31
Allred Rochow Electronegativity: 3.2
Mulliken-Jaffe Electronegativity: 3.19 (12.5% s orbital)
Allen Electronegativity: 3.242
Pauling Electropositivity: N/A
Reflectivity (%): N/A
Refractive Index: 1.000281
Electrons: 18
Protons: 18
Neutrons: 22
Electron Configuration: [Ne] 3s2 3p6
Atomic Radius: N/A
Atomic Radius,
non-bonded (Å):
Covalent Radius: 106±10 pm
Covalent Radius (Å): 1.01
Van der Waals Radius: 188 pm
Oxidation States: 0
Phase: Gas
Crystal Structure: face-centered cubic
Magnetic Ordering: diamagnetic
Electron Affinity (kJ·mol-1) Not stable
1st Ionization Energy: 1520.58 kJ·mol-1
2nd Ionization Energy: 2665.88 kJ·mol-1
3rd Ionization Energy: 3930.84 kJ·mol-1
CAS Number: 7440-37-1
EC Number: 231-147-0
MDL Number: MFCD00003431
Beilstein Number: N/A
SMILES Identifier: [Ar]
InChI Identifier: InChI=1S/Ar
PubChem CID: 23968
ChemSpider ID: 22407
Earth - Total: 2.20E-8 cm^3/g 
Mercury - Total: N/A
Venus - Total:  210E-8 cm^3/g 
Earth - Seawater (Oceans), ppb by weight: 450
Earth - Seawater (Oceans), ppb by atoms: 70
Earth -  Crust (Crustal Rocks), ppb by weight: 1500
Earth -  Crust (Crustal Rocks), ppb by atoms: 780
Sun - Total, ppb by weight: 70000
Sun - Total, ppb by atoms: 2000
Stream, ppb by weight: N/A
Stream, ppb by atoms: N/A
Meterorite (Carbonaceous), ppb by weight: N/A
Meterorite (Carbonaceous), ppb by atoms: N/A
Typical Human Body, ppb by weight: N/A
Typical Human Body, ppb by atom: N/A
Universe, ppb by weight: 200000
Universe, ppb by atom: 6000
Discovered By: Lord Rayleigh and William Ramsay
Discovery Date: 1894
First Isolation: Lord Rayleigh and William Ramsay (1894)

Argon Isotopes

Argon has three stable isotopes: 36Ar, 38Ar, and 40Ar.

Nuclide Isotopic Mass Half-Life Mode of Decay Nuclear Spin Magnetic Moment Binding Energy (MeV) Natural Abundance
(% by atom)
30Ar 30.02156(32)# <20 ns p to 29Cl 0+ N/A 202.6 -
31Ar 31.01212(22)# 14.4(6) ms ß- + p to 30S; ß- to 31Cl; ß- + 2p to 29P; ß- + 3p to 28Si 5/2(+#) N/A 219.06 -
32Ar 31.9976380(19) 98(2) ms ß- to 32Cl; ß- + p to 31S 0+ N/A 241.12 -
33Ar 32.9899257(5) 173.0(20) ms ß- to 33Cl; ß- + p to 32S 1/2+ N/A 256.65 -
34Ar 33.9802712(4) 844.5(34) ms ß+ to 34Cl 0+ N/A 273.11 -
35Ar 34.9752576(8) 1.775(4) s ß+ to 35Cl 3/2+ 0.633 285.85 -
36Ar 35.967545106(29) Observationally Stable - 0+ 0 301.38 0.3365
37Ar 36.96677632(22) 35.04(4) d EC to 37Cl 3/2+ 1.15 310.39 -
38Ar 37.9627324(4) STABLE - 0+ 0 322.2 0.0632
39Ar 38.964313(5) 269(3) y ß- to 39K 7/2- -1.3 328.41 -
40Ar 39.9623831225(29) STABLE - 0+ 0 338.35 99.6003
41Ar 40.9645006(4) 109.61(4) min ß- to 41K 7/2- N/A 344.57 -
42Ar 41.963046(6) 32.9(11) y ß- to 42K 0+ N/A 353.58 -
43Ar 42.965636(6) 5.37(6) min ß- to 43K (5/2-) N/A 359.79 -
44Ar 43.9649240(17) 11.87(5) min ß- to 44K 0+ N/A 368.8 -
45Ar 44.9680400(6) 21.48(15) s ß- to 45K (1/2,3/2,5/2)- N/A 373.16 -
46Ar 45.96809(4) 8.4(6) s ß- to 46K 0+ N/A 381.24 -
47Ar 46.97219(11) 1.23(3) s ß- to 47K; ß- +n to 46K 3/2-# N/A 385.59 -
48Ar 47.97454(32)# 0.48(40) s ß- to 48K 0+ N/A 391.8 -
49Ar 48.98052(54)# 170(50) ms ß- to 49K 3/2-# N/A 394.29 -
50Ar 49.98443(75)# 85(30) ms ß- to 50K 0+ N/A 398.64 -
51Ar 50.99163(75)# 60# ms [>200 ns] ß- to 51K 3/2-# N/A 400.2 -
52Ar 51.99678(97)# 10# ms ß- to 52K 0+ N/A 403.62 -
53Ar 53.00494(107)# 3# ms ß- to 53K; ß- + n to 52K (5/2-)# N/A 404.25 -