10 Argon Facts - Ar or Atomic Number 18

Interesting Argon Element Facts

Green argon lasers are useful for testing the quality of mirrors.
Green argon lasers are useful for testing the quality of mirrors. © Roger Ressmeyer/Corbis/VCG / Getty Images

Argon is atomic number 18 on the periodic table, with the element symbol Ar. Here is a collection of useful and interesting argon element facts.

10 Argon Facts

  1. Argon is a colorless, flavorless, odorless noble gas. Unlike some other gases, it remains colorless even in liquid and solid form. It is nonflammable and nontoxic. However, since argon is 38% more dense than air, it present an asphyxiation risk because it can displace oxygenated air in enclosed spaces.
  1. The element symbol for argon used to be A. In 1957, the International Union of Pure and Applied Chemistry (IUPAC) changed argon's symbol to Ar and mendelevium's symbol from Mv to Md.
  2. Argon was the first discovered noble gas. Henry Cavendish had suspected the element's existence in 1785 from his examination of samples of air. Independent research by H.F. Newall and W.N. Hartley in 1882 revealed a spectral line that could not be assigned to any known element. The element was isolated and officially discovered in air by Lord Rayleigh and William Ramsay in 1894. Rayleigh and Ramsay removed the nitrogen, oxygen, water, and carbon dioxide and examined the remaining gas. Although other elements were present in the residue of air, they accounted for very little of the total mass of the sample.
  3. The element name "argon" comes from the Greek word argos, which means inactive. This refers to the element's resistance to forming chemical bonds.Argon is considered to be chemically inert at room temperature and pressure.
  1. Most of the argon on Earth comes from the radioactive decay of potassium-40 into argon-40. Over 99% of the argon on earth consists of the isotope Ar-40.
  2. The most abundant isotope of argon in the universe is argon-36, which is made when stars with a mass about 11 times greater than the Sun are in their silicon-burning phase. In this phase, an alpha particle (helium nucleus) is added to a silicon-32 nucleus to make sulfur-34, which adds an alpha particle to become argon-36. Some of the argon-36 adds an alpha particle to become calcium-40. In the universe, argon is quite rare.
  1. Argon is the most abundant noble gas. It accounts for about 0.94% of the Earth's atmosphere and about 1.6% of the Martian atmosphere. The thin atmosphere of the planet Mercury is about 70% argon. Not counting water vapor, argon is the third most abundant gas in the Earth's atmosphere, after nitrogen and oxygen. It is produced from fractional distillation of liquid air. In all cases, the most abundant isotope of argon on the planets is Ar-40.
  2. Argon has many uses. It's found in laser, plasma balls, light bulbs, rocket propellant, and glow tubes. It's used as a protective gas for welding, storing sensitive chemicals, and protecting materials. Sometimes pressurized argon is used as a propellant in aerosol cans. Argon-39 radioisotope dating is used to date the age of ground water and ice core samples. Liquid argon is used in cryosurgery, to destroy cancerous tissue. Argon plasma beams and laser beams are also used in medicine. Argon may be used to make a breathing mix called Argox to help remove dissolved nitrogen from the blood during decompression, as from deep-sea diving. Liquid argon is used in scientific experiments, including neutrino experiments and dark matter searches. Although argon is an abundant element, it has no known biological functions.
  1. Argon emits a blue-violet glow when it is excited. Argon lasers exhibit a characteristic blue-green glow.
  2. Because noble gas atoms have a complete valence electron shell, they are not very reactive. Argon does not readily form compounds. No stable compounds are known at room temperature and pressure, although argon fluorohydride (HArF) has been observed at temperatures below 17K. Argon forms clathrates with water. Ions, such as ArH+, and complexes in the excited state, such as ArF, have been seen. Scientists predict stable argon compounds should exist, although they have not yet been synthesized.

Argon Atomic Data

Atomic Number18
Atomic Mass39.948
Melting Point83.81 K ​(−189.34 °C, ​−308.81 °F)
Boiling Point87.302 K ​(−185.848 °C, ​−302.526 °F)
Density1.784 grams per cubic centimeter
Element Groupnoble gas, group 18
Element Period3
Oxidation Number0
Approximate Cost50 cents for 100 grams
Electron Configuration1s22s22p63s23p6
Crystal Structureface-entered cubic (fcc)
Phase at STPgas
Oxidation State0
Electronegativityno value on the Pauling scale

Bonus Argon Joke

Why don't I tell chemistry jokes? All the good ones argon!