Argon
Table:
Argon, 18Ar

Argon
Pronunciation	/ˈɑːrɡɒn/ ⓘ ​(AR-gon)
Appearance	colorless gas exhibiting a lilac/violet glow when placed in an electric field

Standard atomic weight Ar°(Ar)

[39.792, 39.963][1]
39.95±0.16 (abridged)[2]

Argon in the periodic table

Hydrogen

Helium

Lithium

Beryllium

Boron

Carbon

Nitrogen

Oxygen

Fluorine

Neon

Sodium

Magnesium

Aluminium

Silicon

Phosphorus

Sulfur

Chlorine

Argon

Potassium

Calcium

Scandium

Titanium

Vanadium

Chromium

Manganese

Iron

Cobalt

Nickel

Copper

Zinc

Gallium

Germanium

Arsenic

Selenium

Bromine

Krypton

Rubidium

Strontium

Yttrium

Zirconium

Niobium

Molybdenum

Technetium

Ruthenium

Rhodium

Palladium

Silver

Cadmium

Indium

Tin

Antimony

Tellurium

Iodine

Xenon

Caesium

Barium

Lanthanum

Cerium

Praseodymium

Neodymium

Promethium

Samarium

Europium

Gadolinium

Terbium

Dysprosium

Holmium

Erbium

Thulium

Ytterbium

Lutetium

Hafnium

Tantalum

Tungsten

Rhenium

Osmium

Iridium

Platinum

Gold

Mercury (element)

Thallium

Lead

Bismuth

Polonium

Astatine

Radon

Francium

Radium

Actinium

Thorium

Protactinium

Uranium

Neptunium

Plutonium

Americium

Curium

Berkelium

Californium

Einsteinium

Fermium

Mendelevium

Nobelium

Lawrencium

Rutherfordium

Dubnium

Seaborgium

Bohrium

Hassium

Meitnerium

Darmstadtium

Roentgenium

Copernicium

Nihonium

Flerovium

Moscovium

Livermorium

Tennessine

Oganesson

Ne
↑
Ar
↓
Kr

chlorine ← argon → potassium

Atomic number (Z)	18
Group	group 18 (noble gases)
Period	period 3
Block	p-block
Electron configuration	[Ne] 3s2 3p6
Electrons per shell	2, 8, 8
Physical properties
Phase at STP	gas
Melting point	83.81 K ​(−189.34 °C, ​−308.81 °F)
Boiling point	87.302 K ​(−185.848 °C, ​−302.526 °F)
Density (at STP)	1.784 g/L
when liquid (at b.p.)	1.3954 g/cm3
Triple point	83.8058 K, ​68.89 kPa[3]
Critical point	150.687 K, 4.863 MPa[3]
Heat of fusion	1.18 kJ/mol
Heat of vaporization	6.53 kJ/mol
Molar heat capacity	20.85[4] 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	common: (none)

0[5]
Electronegativity	Pauling scale: no data
Ionization energies

1st: 1520.6 kJ/mol
2nd: 2665.8 kJ/mol
3rd: 3931 kJ/mol
(more)

Covalent radius	106±10 pm
Van der Waals radius	188 pm

Spectral lines of argon
Other properties
Natural occurrence	primordial
Crystal structure	​face-centered cubic (fcc) (cF4)
Lattice constant

a = 546.91 pm (at triple point)[6]
Thermal conductivity	17.72×10−3 W/(m⋅K)
Magnetic ordering	diamagnetic[7]
Molar magnetic susceptibility	−19.6×10−6 cm3/mol[8]
Speed of sound	323 m/s (gas, at 27 °C)
CAS Number	7440-37-1
History
Naming	from the Greek ἀργόν, meaning 'lazy' or 'inactive', in reference to its inertness
Discovery and first isolation	Lord Rayleigh and William Ramsay (1894)
Isotopes of argon

v
e

Main isotopes[9]

Decay

abun­dance

half-life (t1/2)

mode

pro­duct

36Ar

0.334%

stable

37Ar

trace

35 d

ε

37Cl

38Ar

0.0630%

stable

39Ar

trace

268 y

β−

39K

40Ar

99.6%

stable

41Ar

trace

109.34 min

β−

41K

42Ar

synth

32.9 y

β−

42K

Category: Argon

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From the table, determine whether the statement is entailed, neutral, or refuted. Return the result as JSON: {"answer": "YOUR ANSWER"}.

Statement: Argon was discovered in the 20th century.

answer: refuted