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colorless gas exhibiting a lilac/violet glow when placed in an electric field
General properties
Name, symbol, number argon, Ar, 18
Group, period, block 18, 3, p
Standard atomic weight {{{atomic mass}}} g/mol
Electron configuration [Ne] 3s2 3p6
Electrons per shell 2, 8, 8 (Image)
Physical properties
Phase gas
Density (0 °C, 101.325 kPa)
1.784 g/L
Liquid density at b.p. 1.3954 g/cm3
Melting point 83.81 K, −189.34 °C, −308.81 °F
Boiling point 87.302 K, −185.848 °C, −302.526 °F
Triple point 83.8058 K (-189°C), 68.89 kPa
Critical point 150.687 K, 4.863 MPa
Heat of fusion 1.18 kJ/mol
Heat of vaporization 6.53 kJ/mol
Specific heat capacity (25 °C) 20.85 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K)   47 53 61 71 87
Atomic properties
Oxidation states 0
Electronegativity no data (Pauling scale)
Ionization energies
1st: {{{1st ionization energy}}} kJ/mol
2nd: {{{2nd ionization energy}}} kJ/mol
3rd: {{{3rd ionization energy}}} kJ/mol
Covalent radius 106±10 pm
Van der Waals radius 188 pm
Crystal structure face-centered cubic
Magnetic ordering diamagnetic
Thermal conductivity (300 K) 17.72×10−3  W/(m·K)
Speed of sound 323 m/s
CAS registry number 7440-37-1
Most stable isotopes
Main article: Isotopes of argon
iso NA half-life DM DE (MeV) DP
36Ar 0.334% stable
37Ar syn 35 d ε 37Cl
38Ar 0.063% stable
39Ar trace 269 y β 39K
40Ar 99.604% stable
41Ar syn 109.34 min β 41K
42Ar syn 32.9 y β 42K
36Ar and 38Ar content may be as high as 2.07% and 4.3% respectively in natural samples. 40Ar is the remainder in such cases, whose content may be as low as 93.6%.

Argon is a chemical element. The symbol for argon is Ar, and its atomic number (or proton number) is 18. It is a noble gas and no electrons or protons can be lost or gained from this atom.

Argon atoms are found in air. About 1% of the Earth's atmosphere (the air around us) is argon.

Argon is often used when welding steel and similar work, to push away the air around the weld, so the oxygen in the air can't join with the metal being welded.

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