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[change | change source]

Sources[change | change source]

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