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Argon



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chlorineargonpotassium
Ne

Ar

Kr
Appearance
colorless gas exhibiting a lilac/violet glow when placed in a high voltage electric field

Vial containing a violet glowing gas

Spectral lines of argon
General properties
Name, symbol, number argon, Ar, 18
Pronunciation /ˈɑrɡɒn/
Element category noble gases
Group, period, block 183, p
Standard atomic weight 39.948(1)g·mol−1
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. 1.40 g·cm−3
Melting point 83.80 K, −189.35 °C, −308.83 °F
Boiling point 87.30 K, −185.85 °C, −302.53 °F
Triple point 83.8058 K (-189°C), 69 kPa
Critical point 150.87 K, 4.898 MPa
Heat of fusion 1.18 kJ·mol−1
Heat of vaporization 6.43 kJ·mol−1
Specific heat capacity (25 °C) 5R/2 = 20.786 J·mol−1·K−1
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: 1520.6 kJ·mol−1
2nd: 2665.8 kJ·mol−1
3rd: 3931 kJ·mol−1
Covalent radius 106±10 pm
Van der Waals radius 188 pm
Miscellanea
Crystal structure face-centered cubic
Magnetic ordering diamagnetic[1]
Thermal conductivity (300 K) 17.72x10-3  W·m−1·K−1
Speed of sound (gas, 27 °C) 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 0.337% 36Ar is stable with 18 neutrons
37Ar syn 35 d ε 0.813 37Cl
38Ar 0.063% 38Ar is stable with 20 neutrons
39Ar trace 269 y β 0.565 39K
40Ar 99.600% 40Ar is stable with 22 neutrons
41Ar syn 109.34 min β 2.49 41K
42Ar syn 32.9 y β 0.600 42K

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.

Related pages

Sources

  1. Magnetic susceptibility of the elements and inorganic compounds, in Handbook of Chemistry and Physics 81st edition, CRC press.