Editorial Feature

Argon (Ar) - Discovery, Occurrence, Production, Properties and Applications of Argon

Chemical Formula

Ar

Background

Argon was discovered by a Scottish chemist, Sir William Ramsay and an English chemist, Lord Rayleigh in 1894. However, an English scientist, Henry Cavendish identified the presence of argon 200 years before its discovery when he found a small amount of gas left behind while separating nitrogen and oxygen from air. Although he anticipated the presence of another element in the air, he was unable to confirm that. Ramsay repeated Cavendish's experiment in 1894 and analyzed the left over unknown gas using spectroscopy. Meanwhile, Rayleigh was also performing the same experiment, almost at the same time. Both the scientists together revealed the unidentified gas and named it Argon.

Basic Information

Name Argon
Symbol Ar
Atomic number 18
Atomic weight 39.948 amu
Standard state Gas at 298 K
CAS Registry ID 7440-37-1
Group in periodic table 18
Group name Noble gas
Period in periodic table 3
Block in periodic table p-block
Color Colorless
Classification Non-metallic
Melting point 83.80 K (-189.35°C or -308.83°F)
Boiling point 87.30 K (-185.85°C or -302.53°F)
Density 0.00178 g/cm3
Phase at room temperature Gas

Occurrence

Argon accounts for nearly 0.93% of the atmosphere and the concentration of argon in the Earth's crust is around 4 ppm.

Isotopes

Argon has 24 known isotopes with mass numbers from 30Ar to 53Ar. Of these, three isotopes, 36Ar, 38Ar, and 40Ar are stable and occur naturally. There are also six radioactive isotopes of Argon.

Production

Argon is industrially extracted from liquid air in a cryogenic air separation unit by means of fractional distillation. When nitrogen gas present in the atmosphere is heated using hot calcium or magnesium, a nitride is formed leaving behind small amount of argon as an impurity. It can also be obtained as a by-product while purifying natural gas.

Health Aspects

The mixing of argon with air can cause super-saturation that in turn increases the risk of suffocation in a confined environment. Excessive inhalation of argon can result in loss of consciousness, vomiting, nausea, dizziness and even death if left untreated. In addition, exposure to rapidly expanding argon gas or cryogenic liquid can cause frostbite or burns.

Key Properties

The key properties of argon are listed below:

  • It is an odorless, tasteless, colorless, inert gas
  • It is chemically inactive and hence it tends to form weak structures at extreme conditions
  • It exists as charged ion molecules.

Applications

The major applications of argon include the following:

  • Electric lamps as filler gas
  • Welding purpose
  • Discharge tubes
  • Argon lasers and argon-dye lasers

References

G.P. Thomas

Written by

G.P. Thomas

Gary graduated from the University of Manchester with a first-class honours degree in Geochemistry and a Masters in Earth Sciences. After working in the Australian mining industry, Gary decided to hang up his geology boots and turn his hand to writing. When he isn't developing topical and informative content, Gary can usually be found playing his beloved guitar, or watching Aston Villa FC snatch defeat from the jaws of victory.

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