Argon

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 Number18
Atomic Weight39.948
Mass Number40
Group18
Period3
Blockp
Protons18 p+
Neutrons22 n0
Electrons18 e-
Argon ice 1.jpg Animated Bohr Model of Ar (Argon) Enhanced Bohr Model of Ar (Argon) Bohr Model: Ar (Argon) Orbital Diagram of Ar (Argon)

Properties

Atomic Radius
71 pm
Molar Volume
Covalent Radius
96 pm
Metallic Radius
Ionic Radius
Crystal Radius
Van der Waals Radius
188 pm
Density
0.001633 g/cm³
Energy
Proton Affinity
369.2 kJ/mol
Electron Affinity
Ionization Energy
15.7596112 eV/particle
Heat of Vaporization
6.52 kJ/mol
Heat of Fusion
Heat of Formation
Electrons
Electron Shells2, 8, 8
Valence Electrons0
Electron Configuration[Ne] 3s2 3p6
Oxidation States0
Electronegativity
Electrophilicity
0.0832013314590371 eV/particle
Phases
PhaseGas
Gas PhaseMonoatomic
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
Appearancecolorless 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
Heat Capacity Ratio (Adiabatic Index)5/3
Electrical Properties
Type
Electrical Conductivity
Electrical Resistivity
Superconducting Point
Magnetism
Typediamagnetic
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 StructureFace Centered Cubic (FCC)
Lattice Constant
5.26 Å
Lattice Anglesπ/2, π/2, π/2
Mechanical Properties
Hardness
Bulk Modulus
Shear Modulus
Young Modulus
Poisson Ratio
Speed of Sound
319 m/s
Classification
CategoryNoble gases, Noble gases
CAS GroupVIII
IUPAC GroupVIIIA
Glawe Number3
Mendeleev Number114
Pettifor Number3
Geochemical Classvolatile
Goldschmidt Classatmophile
Other
Gas Basicity
346.3 kJ/mol
Dipole Polarizability
11.083 ± 0.007 a₀
C6 Dispersion Coefficient
64.2 a₀
Allotropes
Neutron Cross Section
0.66
Neutron Mass Absorption
0.00059
Quantum Numbers1S0
Space Group225 (Fm_3m)

Isotopes of Argon

Stable Isotopes3
Unstable Isotopes23
Radioactive Isotopes22

29Ar

Abundance
Relative Atomic Mass
29.040761 ± 0.000471 Da
Mass Number29
G-Factor
Half Life
Spin5/2
Quadrupole Moment
Discovery Year2018
Parity+

29Ar Decay Modes
Decay ModeIntensity
2p (2-proton emission)100%

30Ar

AbundanceRadioactive ☢️
Relative Atomic Mass
30.023694 ± 0.000192 Da
Mass Number30
G-Factor
0
Half Life
Spin0
Quadrupole Moment
0
Discovery Year2015
Parity+

30Ar Decay Modes
Decay ModeIntensity
2p (2-proton emission)100%

31Ar

AbundanceRadioactive ☢️
Relative Atomic Mass
31.012158 ± 0.000215 Da
Mass Number31
G-Factor
Half Life
15 ± 0.3 ms
Spin5/2
Quadrupole Moment
Discovery Year1986
Parity+

31Ar Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%
β+ p (β+-delayed proton emission)68.3%
2p (2-proton emission)9%
B+pA0.38%
3p0.07%
β+α (β+-delayed α emission)0.03%
2p (2-proton emission)0.0006%

32Ar

AbundanceRadioactive ☢️
Relative Atomic Mass
31.997637824 ± 0.0000019 Da
Mass Number32
G-Factor
0
Half Life
98 ± 2 ms
Spin0
Quadrupole Moment
0
Discovery Year1977
Parity+

32Ar Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%
β+ p (β+-delayed proton emission)35.58%

33Ar

AbundanceRadioactive ☢️
Relative Atomic Mass
32.989925545 ± 0.00000043 Da
Mass Number33
G-Factor
-1.446 ± 0.012
Half Life
173 ± 2 ms
Spin1/2
Quadrupole Moment
0
Discovery Year1964
Parity+

33Ar Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%
β+ p (β+-delayed proton emission)38.7%

34Ar

AbundanceRadioactive ☢️
Relative Atomic Mass
33.980270092 ± 0.000000083 Da
Mass Number34
G-Factor
0
Half Life
846.46 ± 0.35 ms
Spin0
Quadrupole Moment
0
Discovery Year1966
Parity+

34Ar Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%

35Ar

AbundanceRadioactive ☢️
Relative Atomic Mass
34.975257719 ± 0.00000073 Da
Mass Number35
G-Factor
0.42133333333333 ± 0.00013333333333333
Half Life
1.7756 ± 0.001 s
Spin3/2
Quadrupole Moment
-0.084 ± 0.015
Discovery Year1940
Parity+

35Ar Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%

36Ar

Abundance
0.3336 ± 0.021
Relative Atomic Mass
35.967545106 ± 0.000000028 Da
Mass Number36
G-Factor
0
Half Life
Spin0
Quadrupole Moment
0
Discovery Year1920
Parity+

36Ar Decay Modes
Decay ModeIntensity
+ (double β+ decay)%

37Ar

AbundanceRadioactive ☢️
Relative Atomic Mass
36.966776301 ± 0.000000221 Da
Mass Number37
G-Factor
Half Life
35.011 ± 0.019 d
Spin3/2
Quadrupole Moment
0.076 ± 0.003
Discovery Year1941
Parity+

37Ar Decay Modes
Decay ModeIntensity
ϵ (electron capture)100%

38Ar

Abundance
0.0629 ± 0.007
Relative Atomic Mass
37.962732102 ± 0.000000209 Da
Mass Number38
G-Factor
0
Half Life
Spin0
Quadrupole Moment
0
Discovery Year1934
Parity+

39Ar

AbundanceRadioactive ☢️
Relative Atomic Mass
38.964313037 ± 0.000005367 Da
Mass Number39
G-Factor
-0.45428571428571 ± 0.0042857142857143
Half Life
268 ± 8 y
Spin7/2
Quadrupole Moment
-0.116 ± 0.002
Discovery Year1950
Parity-

39Ar Decay Modes
Decay ModeIntensity
β (β decay)100%

40Ar

Abundance
99.6035 ± 0.025
Relative Atomic Mass
39.96238312204 ± 0.00000000234 Da
Mass Number40
G-Factor
0
Half Life
Spin0
Quadrupole Moment
0
Discovery Year1920
Parity+

41Ar

AbundanceRadioactive ☢️
Relative Atomic Mass
40.96450057 ± 0.000000372 Da
Mass Number41
G-Factor
-0.37428571428571 ± 0.0022857142857143
Half Life
109.61 ± 0.04 m
Spin7/2
Quadrupole Moment
-0.042 ± 0.004
Discovery Year1936
Parity-

41Ar Decay Modes
Decay ModeIntensity
β (β decay)100%

42Ar

AbundanceRadioactive ☢️
Relative Atomic Mass
41.963045737 ± 0.0000062 Da
Mass Number42
G-Factor
0
Half Life
32.9 ± 1.1 y
Spin0
Quadrupole Moment
0
Discovery Year1952
Parity+

42Ar Decay Modes
Decay ModeIntensity
β (β decay)100%

43Ar

AbundanceRadioactive ☢️
Relative Atomic Mass
42.965636056 ± 0.0000057 Da
Mass Number43
G-Factor
-0.4088 ± 0.0024
Half Life
5.37 ± 0.06 m
Spin5/2
Quadrupole Moment
0.142 ± 0.014
Discovery Year1969
Parity

43Ar Decay Modes
Decay ModeIntensity
β (β decay)100%

44Ar

AbundanceRadioactive ☢️
Relative Atomic Mass
43.964923814 ± 0.0000017 Da
Mass Number44
G-Factor
0
Half Life
11.87 ± 0.05 m
Spin0
Quadrupole Moment
0
Discovery Year1969
Parity+

44Ar Decay Modes
Decay ModeIntensity
β (β decay)100%

45Ar

AbundanceRadioactive ☢️
Relative Atomic Mass
44.968039731 ± 0.00000055 Da
Mass Number45
G-Factor
Half Life
21.48 ± 0.15 s
Spin5/2
Quadrupole Moment
Discovery Year1974
Parity-

45Ar Decay Modes
Decay ModeIntensity
β (β decay)100%

46Ar

AbundanceRadioactive ☢️
Relative Atomic Mass
45.968039244 ± 0.0000025 Da
Mass Number46
G-Factor
0
Half Life
8.4 ± 0.6 s
Spin0
Quadrupole Moment
0
Discovery Year1974
Parity+

46Ar Decay Modes
Decay ModeIntensity
β (β decay)100%

47Ar

AbundanceRadioactive ☢️
Relative Atomic Mass
46.972767112 ± 0.0000013 Da
Mass Number47
G-Factor
Half Life
1.23 ± 0.03 s
Spin3/2
Quadrupole Moment
Discovery Year1985
Parity

47Ar Decay Modes
Decay ModeIntensity
β (β decay)100%
β n (β-delayed neutron emission)0.2%

48Ar

AbundanceRadioactive ☢️
Relative Atomic Mass
47.976001 ± 0.000018 Da
Mass Number48
G-Factor
0
Half Life
415 ± 15 ms
Spin0
Quadrupole Moment
0
Discovery Year2004
Parity+

48Ar Decay Modes
Decay ModeIntensity
β (β decay)100%
β n (β-delayed neutron emission)38%

49Ar

AbundanceRadioactive ☢️
Relative Atomic Mass
48.981685 ± 0.000429 Da
Mass Number49
G-Factor
Half Life
236 ± 8 ms
Spin3/2
Quadrupole Moment
Discovery Year1989
Parity-

49Ar Decay Modes
Decay ModeIntensity
β (β decay)100%
β n (β-delayed neutron emission)29%
2n (2-neutron emission)%

50Ar

AbundanceRadioactive ☢️
Relative Atomic Mass
49.985797 ± 0.000537 Da
Mass Number50
G-Factor
0
Half Life
106 ± 6 ms
Spin0
Quadrupole Moment
0
Discovery Year1989
Parity+

50Ar Decay Modes
Decay ModeIntensity
β (β decay)100%
β n (β-delayed neutron emission)37%
2n (2-neutron emission)%

51Ar

AbundanceRadioactive ☢️
Relative Atomic Mass
50.993033 ± 0.000429 Da
Mass Number51
G-Factor
Half Life
Spin1/2
Quadrupole Moment
0
Discovery Year1989
Parity-

51Ar Decay Modes
Decay ModeIntensity
β (β decay)%
β n (β-delayed neutron emission)%
2n (2-neutron emission)%

52Ar

AbundanceRadioactive ☢️
Relative Atomic Mass
51.998519 ± 0.000644 Da
Mass Number52
G-Factor
0
Half Life
Spin0
Quadrupole Moment
0
Discovery Year2009
Parity+

52Ar Decay Modes
Decay ModeIntensity
β (β decay)%
β n (β-delayed neutron emission)%
2n (2-neutron emission)%

53Ar

AbundanceRadioactive ☢️
Relative Atomic Mass
53.00729 ± 0.00075 Da
Mass Number53
G-Factor
Half Life
Spin5/2
Quadrupole Moment
Discovery Year2009
Parity-

53Ar Decay Modes
Decay ModeIntensity
β (β decay)%
β n (β-delayed neutron emission)%
2n (2-neutron emission)%

54Ar

AbundanceRadioactive ☢️
Relative Atomic Mass
54.013484 ± 0.000859 Da
Mass Number54
G-Factor
0
Half Life
Spin0
Quadrupole Moment
0
Discovery Year2018
Parity+

54Ar Decay Modes
Decay ModeIntensity
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

DiscoverersSir William Ramsey, Baron Rayleigh
Discovery LocationScotland
Discovery Year1894
Etymology (Name Origin)Greek: argos (inactive).
PronunciationAR-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

1s0.4925
2p3.9918
2s5.7696
3p11.2359
3s10.2432