Argon (Ar)

Monatomic noble gas. Makes up 0.93% of the air. Colourless, odorless. Is inert and has no true compounds. Lord Rayleigh and Sir william Ramsey identified argon in 1894.

Atomic Number	18
Atomic Weight	39.948
Mass Number	40

Group	18
Period	3
Block	p

Protons	18 p⁺
Neutrons	22 n⁰
Electrons	18 e^-

Properties

Energy
Atomic Radius	71 pm 197 pm
Molar Volume	24.2 cm³/mol
Covalent Radius	96 pm 107 pm 96 pm 106 pm
Metallic Radius
Ionic Radius
Crystal Radius
Van der Waals Radius	188 pm 188 pm 199 pm 386.8 pm
Density	0.001633 g/cm³
Proton Affinity	369.2 kJ/mol
Electron Affinity	-11.5 eV/particle
Ionization Energy	15.7596112 eV/particle 27.62967 eV/particle 40.735 eV/particle 59.58 eV/particle 74.84 eV/particle 91.29 eV/particle 124.412 eV/particle 143.4567 eV/particle 422.598 eV/particle 479.76 eV/particle 540.43 eV/particle 618.95 eV/particle 685.47 eV/particle 755.13 eV/particle 855.47 eV/particle 918.374 eV/particle 4,120.6655 eV/particle 4,426.2227 eV/particle
Heat of Vaporization	6.52 kJ/mol
Heat of Fusion
Heat of Formation
Electrons
Electron Shells	2, 8, 8
Valence Electrons	0
Electron Configuration	[Ne] 3s² 3p⁶
Oxidation States	0
Electronegativity	19.17 eV/particle 0.2922
Electrophilicity	0.0832013314590371 eV/particle
Phases
Phase	Gas
Gas Phase	Monoatomic
Boiling Point	87.302 K
Melting Point	83.81 K
Critical Pressure	4.863 MPa
Critical Temperature	150.687 K
Triple Point	83.8058 K 68.89 kPa
Visual
Color	Colorless #ff1493 #80d1e3 #80d1e3
Appearance	colorless gas exhibiting a lilac/violet glow when placed in a high voltage electric field
Refractive Index	1.000281
Thermodynamic Properties
Thermal Conductivity	0.0177 W/(m K)
Thermal Expansion
Molar Heat Capacity	20.786 J/(mol K)
Specific Heat Capacity	0.52 J/(g⋅K)
Heat Capacity Ratio (Adiabatic Index)	5/3
Electrical Properties
Type
Electrical Conductivity
Electrical Resistivity
Superconducting Point
Magnetism
Type	diamagnetic
Magnetic Susceptibility (Mass)	-0.000000006 m³/Kg
Magnetic Susceptibility (Molar)	-0.00000000024 m³/mol
Magnetic Susceptibility (Volume)	-0.0000000107
Magnetic Ordering
Curie Point
Neel Point
Structure
Crystal Structure	Face Centered Cubic (FCC)
Lattice Constant	5.26 Å
Lattice Angles	π/2, π/2, π/2
Mechanical Properties
Hardness
Bulk Modulus
Shear Modulus
Young Modulus
Poisson Ratio
Speed of Sound	319 m/s
Classification
Category	Noble gases, Noble gases
CAS Group	VIII
IUPAC Group	VIIIA
Glawe Number	3
Mendeleev Number	114
Pettifor Number	3
Geochemical Class	volatile
Goldschmidt Class	atmophile
Other
Gas Basicity	346.3 kJ/mol
Dipole Polarizability	11.083 ± 0.007 a₀
C6 Dispersion Coefficient	64.2 a₀ 67.4 a₀
Allotropes
Neutron Cross Section	0.66
Neutron Mass Absorption	0.00059
Quantum Numbers	1S0
Space Group	225 (Fm_3m)

Isotopes of Argon

Stable Isotopes	3
Unstable Isotopes	23
Radioactive Isotopes	22

²⁹Ar

Abundance
Relative Atomic Mass	29.040761 ± 0.000471 Da
Mass Number	29
G-Factor
Half Life
Spin	5/2
Quadrupole Moment
Discovery Year	2018
Parity	+

²⁹Ar Decay Modes

Decay Mode	Intensity
2p (2-proton emission)	100%

³⁰Ar

Abundance	Radioactive ☢️
Relative Atomic Mass	30.023694 ± 0.000192 Da
Mass Number	30
G-Factor	0
Half Life
Spin	0
Quadrupole Moment	0
Discovery Year	2015
Parity	+

³⁰Ar Decay Modes

Decay Mode	Intensity
2p (2-proton emission)	100%

³¹Ar

Abundance	Radioactive ☢️
Relative Atomic Mass	31.012158 ± 0.000215 Da
Mass Number	31
G-Factor
Half Life	15 ± 0.3 ms
Spin	5/2
Quadrupole Moment
Discovery Year	1986
Parity	+

³¹Ar Decay Modes

Decay Mode	Intensity
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	100%
β⁺ p (β⁺-delayed proton emission)	68.3%
2p (2-proton emission)	9%
B+pA	0.38%
3p	0.07%
β⁺α (β⁺-delayed α emission)	0.03%
2p (2-proton emission)	0.0006%

³²Ar

Abundance	Radioactive ☢️
Relative Atomic Mass	31.997637824 ± 0.0000019 Da
Mass Number	32
G-Factor	0
Half Life	98 ± 2 ms
Spin	0
Quadrupole Moment	0
Discovery Year	1977
Parity	+

³²Ar Decay Modes

Decay Mode	Intensity
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	100%
β⁺ p (β⁺-delayed proton emission)	35.58%

³³Ar

Abundance	Radioactive ☢️
Relative Atomic Mass	32.989925545 ± 0.00000043 Da
Mass Number	33
G-Factor	-1.446 ± 0.012
Half Life	173 ± 2 ms
Spin	1/2
Quadrupole Moment	0
Discovery Year	1964
Parity	+

³³Ar Decay Modes

Decay Mode	Intensity
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	100%
β⁺ p (β⁺-delayed proton emission)	38.7%

³⁴Ar

Abundance	Radioactive ☢️
Relative Atomic Mass	33.980270092 ± 0.000000083 Da
Mass Number	34
G-Factor	0
Half Life	846.46 ± 0.35 ms
Spin	0
Quadrupole Moment	0
Discovery Year	1966
Parity	+

³⁴Ar Decay Modes

Decay Mode	Intensity
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	100%

³⁵Ar

Abundance	Radioactive ☢️
Relative Atomic Mass	34.975257719 ± 0.00000073 Da
Mass Number	35
G-Factor	0.42133333333333 ± 0.00013333333333333
Half Life	1.7756 ± 0.001 s
Spin	3/2
Quadrupole Moment	-0.084 ± 0.015
Discovery Year	1940
Parity	+

³⁵Ar Decay Modes

Decay Mode	Intensity
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	100%

³⁶Ar

Abundance	0.3336 ± 0.021
Relative Atomic Mass	35.967545106 ± 0.000000028 Da
Mass Number	36
G-Factor	0
Half Life
Spin	0
Quadrupole Moment	0
Discovery Year	1920
Parity	+

³⁶Ar Decay Modes

Decay Mode	Intensity
2β⁺ (double β⁺ decay)	%

³⁷Ar

Abundance	Radioactive ☢️
Relative Atomic Mass	36.966776301 ± 0.000000221 Da
Mass Number	37
G-Factor
Half Life	35.011 ± 0.019 d
Spin	3/2
Quadrupole Moment	0.076 ± 0.003
Discovery Year	1941
Parity	+

³⁷Ar Decay Modes

Decay Mode	Intensity
ϵ (electron capture)	100%

³⁸Ar

Abundance	0.0629 ± 0.007
Relative Atomic Mass	37.962732102 ± 0.000000209 Da
Mass Number	38
G-Factor	0
Half Life
Spin	0
Quadrupole Moment	0
Discovery Year	1934
Parity	+

³⁹Ar

Abundance	Radioactive ☢️
Relative Atomic Mass	38.964313037 ± 0.000005367 Da
Mass Number	39
G-Factor	-0.45428571428571 ± 0.0042857142857143
Half Life	268 ± 8 y
Spin	7/2
Quadrupole Moment	-0.116 ± 0.002
Discovery Year	1950
Parity	-

³⁹Ar Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	100%

⁴⁰Ar

Abundance	99.6035 ± 0.025
Relative Atomic Mass	39.96238312204 ± 0.00000000234 Da
Mass Number	40
G-Factor	0
Half Life
Spin	0
Quadrupole Moment	0
Discovery Year	1920
Parity	+

⁴¹Ar

Abundance	Radioactive ☢️
Relative Atomic Mass	40.96450057 ± 0.000000372 Da
Mass Number	41
G-Factor	-0.37428571428571 ± 0.0022857142857143
Half Life	109.61 ± 0.04 m
Spin	7/2
Quadrupole Moment	-0.042 ± 0.004
Discovery Year	1936
Parity	-

⁴¹Ar Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	100%

⁴²Ar

Abundance	Radioactive ☢️
Relative Atomic Mass	41.963045737 ± 0.0000062 Da
Mass Number	42
G-Factor	0
Half Life	32.9 ± 1.1 y
Spin	0
Quadrupole Moment	0
Discovery Year	1952
Parity	+

⁴²Ar Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	100%

⁴³Ar

Abundance	Radioactive ☢️
Relative Atomic Mass	42.965636056 ± 0.0000057 Da
Mass Number	43
G-Factor	-0.4088 ± 0.0024
Half Life	5.37 ± 0.06 m
Spin	5/2
Quadrupole Moment	0.142 ± 0.014
Discovery Year	1969
Parity

⁴³Ar Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	100%

⁴⁴Ar

Abundance	Radioactive ☢️
Relative Atomic Mass	43.964923814 ± 0.0000017 Da
Mass Number	44
G-Factor	0
Half Life	11.87 ± 0.05 m
Spin	0
Quadrupole Moment	0
Discovery Year	1969
Parity	+

⁴⁴Ar Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	100%

⁴⁵Ar

Abundance	Radioactive ☢️
Relative Atomic Mass	44.968039731 ± 0.00000055 Da
Mass Number	45
G-Factor
Half Life	21.48 ± 0.15 s
Spin	5/2
Quadrupole Moment
Discovery Year	1974
Parity	-

⁴⁵Ar Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	100%

⁴⁶Ar

Abundance	Radioactive ☢️
Relative Atomic Mass	45.968039244 ± 0.0000025 Da
Mass Number	46
G-Factor	0
Half Life	8.4 ± 0.6 s
Spin	0
Quadrupole Moment	0
Discovery Year	1974
Parity	+

⁴⁶Ar Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	100%

⁴⁷Ar

Abundance	Radioactive ☢️
Relative Atomic Mass	46.972767112 ± 0.0000013 Da
Mass Number	47
G-Factor
Half Life	1.23 ± 0.03 s
Spin	3/2
Quadrupole Moment
Discovery Year	1985
Parity

⁴⁷Ar Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	100%
β⁻ n (β⁻-delayed neutron emission)	0.2%

⁴⁸Ar

Abundance	Radioactive ☢️
Relative Atomic Mass	47.976001 ± 0.000018 Da
Mass Number	48
G-Factor	0
Half Life	415 ± 15 ms
Spin	0
Quadrupole Moment	0
Discovery Year	2004
Parity	+

⁴⁸Ar Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	100%
β⁻ n (β⁻-delayed neutron emission)	38%

⁴⁹Ar

Abundance	Radioactive ☢️
Relative Atomic Mass	48.981685 ± 0.000429 Da
Mass Number	49
G-Factor
Half Life	236 ± 8 ms
Spin	3/2
Quadrupole Moment
Discovery Year	1989
Parity	-

⁴⁹Ar Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	100%
β⁻ n (β⁻-delayed neutron emission)	29%
2n (2-neutron emission)	%

⁵⁰Ar

Abundance	Radioactive ☢️
Relative Atomic Mass	49.985797 ± 0.000537 Da
Mass Number	50
G-Factor	0
Half Life	106 ± 6 ms
Spin	0
Quadrupole Moment	0
Discovery Year	1989
Parity	+

⁵⁰Ar Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	100%
β⁻ n (β⁻-delayed neutron emission)	37%
2n (2-neutron emission)	%

⁵¹Ar

Abundance	Radioactive ☢️
Relative Atomic Mass	50.993033 ± 0.000429 Da
Mass Number	51
G-Factor
Half Life
Spin	1/2
Quadrupole Moment	0
Discovery Year	1989
Parity	-

⁵¹Ar Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	%
β⁻ n (β⁻-delayed neutron emission)	%
2n (2-neutron emission)	%

⁵²Ar

Abundance	Radioactive ☢️
Relative Atomic Mass	51.998519 ± 0.000644 Da
Mass Number	52
G-Factor	0
Half Life
Spin	0
Quadrupole Moment	0
Discovery Year	2009
Parity	+

⁵²Ar Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	%
β⁻ n (β⁻-delayed neutron emission)	%
2n (2-neutron emission)	%

⁵³Ar

Abundance	Radioactive ☢️
Relative Atomic Mass	53.00729 ± 0.00075 Da
Mass Number	53
G-Factor
Half Life
Spin	5/2
Quadrupole Moment
Discovery Year	2009
Parity	-

⁵³Ar Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	%
β⁻ n (β⁻-delayed neutron emission)	%
2n (2-neutron emission)	%

⁵⁴Ar

Abundance	Radioactive ☢️
Relative Atomic Mass	54.013484 ± 0.000859 Da
Mass Number	54
G-Factor	0
Half Life
Spin	0
Quadrupole Moment	0
Discovery Year	2018
Parity	+

⁵⁴Ar Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	%
β⁻ n (β⁻-delayed neutron emission)	%
2n (2-neutron emission)	%

History

Argon was suspected to be present in air by Henry Cavendish in 1785. It was not isolated until 1894 by Lord Rayleigh and Sir William Ramsay in Scotland. Argon became the first member of the noble gases to be discovered. In 1957, IUPAC agreed that the symbol should change from A to Ar. From the Greek argos, inactive

Discoverers	Sir William Ramsey, Baron Rayleigh
Discovery Location	Scotland
Discovery Year	1894
Etymology (Name Origin)	Greek: argos (inactive).
Pronunciation	AR-gon (English)

Argon is considered to be non-toxic

Argon makes a distinctive blue-green gas laser

Uses

Argon gas is used to fill conventional incandescent and fluorescent light bulbs. Argon is also used as an inert gas shield for arc welding and cutting, as blanket for the production of titanium and other reactive elements. It is used as a protective atmosphere for growing silicon and germanium crystals. Used in lighting products. It is often used in filling incandescent light bulbs. Some is mixed with krypton in fluorescent lamps. Crystals in the semiconductor industry are grown in argon atmospheres.

Sources

Continuously released into the air by decay of radioactive potassium-40. Pure form is obtained from fractional distillation of liquid air.

Abundance
Abundance in Earth's crust	3.5 mg/kg
Abundance in Oceans	0.45 mg/L
Abundance in Human Body
Abundance in Meteor
Abundance in Sun	0.007 %
Abundance in Universe	0.02 %

Nuclear Screening Constants

1	s	0.4925
2	p	3.9918
2	s	5.7696
3	p	11.2359
3	s	10.2432

Argon on ChemicalAid

Art & Architecture Thesaurus ID	300133261
Australian Educational Vocabulary ID	scot/1608
BNCF Thesaurus ID	30962
Bibliothèque nationale de France ID	119700051
Brockhaus Enzyklopädie online ID	argon
CAB ID	42654
CAS Registry Number	7440-37-1
ChEBI ID	49475
ChemSpider ID	22407
CosIng number	54501
DSSTOX compound identifier	DTXCID0031055
DSSTox substance ID	DTXSID3052482
Den Store Danske ID	argon
ECHA Substance Infocard ID	100.028.315
Encyclopædia Universalis ID	argon
E number	E938
Freebase ID	/m/027r9df
French Vikidia ID	Argon
GND ID	4142990-4
Gran Enciclopèdia Catalana ID	0004615
Great Russian Encyclopedia Online ID	1827507
Gujarati Vishwakosh entry	આગૉર્ન
HSDB ID	7902
ICSC ID	0154
InChI	InChI=1S/Ar
InChIKey	XKRFYHLGVUSROY-UHFFFAOYSA-N
KBpedia ID	Argon
Latvian National Encyclopedia Online ID	133180
Library of Congress authority ID	sh85007108
MeSH descriptor ID	D001128
National Diet Library ID	00575518
National Library of Israel J9U ID	987007295519905171
OmegaWiki Defined Meaning	15591
OpenAlex ID	C547737533
OpenAlex ID	C2992172976
Open Food Facts ingredient ID	propellent-gas-e938
PDB ligand ID	AR
PDB structure ID	1C6F
PDB structure ID	1C6I
PDB structure ID	1C66
PDB structure ID	1C6C
PSH ID	5818
PubChem CID	23968
Quora topic ID	Argon-element
RxNorm ID	1368133
Römpp online ID	RD-01-03226
Spanish Vikidia ID	Argón
Store norske leksikon ID	argon
Treccani Vocabulary ID	argon
U.S. National Archives Identifier	10639898
UK Archival Thesaurus ID	f2/mt225/4347/12165
UNII	67XQY1V3KH
WordNet 3.1 Synset ID	14653098-n
YSO ID	14683
ZVG number	7180

Argon (Ar)

Properties

Isotopes of Argon

29Ar

29Ar Decay Modes

30Ar

30Ar Decay Modes

31Ar

31Ar Decay Modes

32Ar

32Ar Decay Modes

33Ar

33Ar Decay Modes

34Ar

34Ar Decay Modes

35Ar

35Ar Decay Modes

36Ar

36Ar Decay Modes

37Ar

37Ar Decay Modes

38Ar

39Ar

39Ar Decay Modes

40Ar

41Ar

41Ar Decay Modes

42Ar

42Ar Decay Modes

43Ar

43Ar Decay Modes

44Ar

44Ar Decay Modes

45Ar

45Ar Decay Modes

46Ar

46Ar Decay Modes

47Ar

47Ar Decay Modes

48Ar

48Ar Decay Modes

49Ar

49Ar Decay Modes

50Ar

50Ar Decay Modes

51Ar

51Ar Decay Modes

52Ar

52Ar Decay Modes

53Ar

53Ar Decay Modes

54Ar

54Ar Decay Modes