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Chlorine - Argon

Full table
Name, Symbol, NumberArgon, Ar, 18
Chemical series Noble gases
Group, Period, Block18 (VIIIA), 3 , p
Density, Hardness 1.784 kg/m3 (273 K), NA
Appearance Colorless
Atomic Properties
Atomic weight 39.948 amu
Atomic radius (calc.) no data (71) pm
Covalent radius 97 pm
van der Waals radius 188 pm
Electron configuration [Ne]33s2 3p6
e- 's per energy level2, 8, 8
Oxidation states (Oxide) 0 (unknown)
Crystal structure Cubic face centered
Physical Properties
State of matter gas (nonmagnetic)
Melting point 83.8 K (-308.7 F)
Boiling point 87.3 K (-302.4 F)
Molar volume 22.56 ×1010-3 m3/mol
Heat of vaporization 6.447 kJ/mol
Heat of fusion 1.188 kJ/mol
Vapor pressure NA
Speed of sound 319 m/s at 293.15 K
Electronegativity no data (Pauling scale)
Specific heat capacity 520 J/(kg*K)
Electrical conductivity no data
Thermal conductivity 0.01772 W/(m*K)
1st ionization potential 1520.6 kJ/mol
2nd ionization potential 2665.8 kJ/mol
3rd ionization potential 3931 kJ/mol
4th ionization potential 5771 kJ/mol
5th ionization potential 7238 kJ/mol
6th ionization potential 8781 kJ/mol
7th ionization potential 11995 kJ/mol
8th ionization potential 13842 kJ/mol
Most Stable Isotopes
isoNAhalf-life DMDE MeVDP
36Ar0.336%Ar is stable with 18 neutrons
38Ar0.063%Ar is stable with 20 neutrons
39Ar{syn.}269 yBeta-0.56539K
40Ar99.6%Ar is stable with 22 neutrons
42Ar{syn}32.9 yBeta-0.60042K
SI units & STP are used except where noted.
Argon is a chemical element in the periodic table that has the symbol Ar and atomic number 18. The third noble gas, in period 8, argon makes up about 1% of the Earth's atmosphere.

Table of contents
1 Notable Characteristics
2 Applications
3 History
4 Occurrence
5 Isotopes
6 External Links

Notable Characteristics

Argon is 2.5 times as soluble in water as nitrogen which is approximately the same solubility as oxygen. This chemically inert element is colorless and odorless in both its liquid and gaseous forms. There are no known true chemical compounds that contain argon.


It is used in lighting since it will not react with the filament in a
lightbulb even under high temperatures and other cases where diatomic nitrogen is an unsuitable (semi-)inert gas. Other uses;

Argon is also used in technical SCUBA diving to inflate the drysuit, due to its nonreactive, heat isolating effect.


Argon (
Greek argos meaning "lazy") was suspected to be present in air by Henry Cavendish in 1785 but wasn't discovered until 1894 by Lord Rayleigh and Sir William Ramsay.


This gas is isolated through liquid air fractionation since the
atmosphere contains only 0.94% argon. The Martian atmosphere in contrast contains 1.6% of Ar-40 and 5 ppm Ar-36.


The main
isotopes of argon found on earth are Ar-40, Ar-36, and Ar-38. Naturally occurring K-40 with a half-life of 1.250 x 109 years, decays to stable Ar-40 (11.2%) by electron capture and by positron emission, and also decays to stable Ca-40 (88.8%) by negatron emission. These properties and ratios are used to determine the age of rockss.

In earth's atmosphere, Ar-39 is made by cosmic ray activity, primarily with Ar-40. In the subsurface environment, it is also produced through neutron-capture by K-39 or alpha emission by calcium. Argon-37 is produced from the decay of calcium-40, the result of subsurface nuclear explosions. It has a half-life of 35 days.

External Links