Argon (Ar)

Argon is the third most plentiful natural gas found in the Earth’s atmosphere. It has no color, odor, or taste. With the chemical symbol Ar and atomic number 18, argon is an inert gas belonging to the family of monatomic noble gases in the periodic table of elements. This chemical element is also the first one discovered among the noble gas elements

Chemical and Physical Properties of Argon

Property Value
Name: Argon
Symbol: Ar
Atomic Number: 18
Group: Noble Gas
Crystal Structure: Cubic: Face centered
Atomic Weight: 39.948
Shells: 2,8,8
Orbitals: [Ne] 3s2 3p6
Valence: 0
Melting Point: 83.77
Boiling Point: 87.28
Electro Negativity: 0
Covalent Radius: 0.98 Å
Atomic Radius: 0.88 Å
Atomic Volume: 23.9 cm³/mol
Name Origin: Greek: argos (inactive)
Discovered By: Sir William Ramsey, Baron Rayleigh
Year of discovery: 1894
Location: Scotland
Pronunciation: AR-gon
Oxidation States: 0
Density: 0.0017824 g/cm³
Uses: Used in lighting products, filling incandescent light bulbs, mixed with krypton in fluorescent lamps, and in the semiconductor industry for growing crystals.
Description: Soft, waxy, silver-white metal. Eighth most abundant element in the earth’s crust. Occurs only in compounds.

Argon is an odorless, tasteless, colorless, and inert gas with a molecular density of 1.784 grams per liter. This chemical element with an atomic mass of 39.948 g.mol -1 reaches boiling point at -185.7 °C, while its melting point is at -189 °C. With a van der Waals radius of  0.192 nm, argon shares the solubility properties of oxygen, which makes this gas more water-soluble than nitrogen. 

At -185.86°C (-302.55°F), this natural gas, notable for its inertness, changes its aggregate state from a gas into a liquid. The physical properties of argon are preserved in both of its forms. 

The tendency of the molecule of this inert gas to attract electrons toward its atomic shell is unknown:

 Ar + e– → Ar–        – ∆H = Affinity = — kJ/mol

The thermal conductivity of argon is 17.72 mW m-1K-1 at room temperature. When electricity is discharged through argon under low pressure, it assumes a pale red color. On the other hand, when argon is put under high pressure, the discharged electricity appears steely blue in color. 

How Was Argon Discovered?

The story of argon’s discovery begins in 1785. This was the year when a British scientist of noble descent, Henry Cavendish (10 October 1731 – 24 February 1810), began to investigate atmospheric air. One of his experiments on gas elements left this great chemist puzzled. Namely, Henry Cavendish observed that after extracting oxygen and nitrogen from an atmospheric air sample, there was a 1/120 residue of nitrogen. 

A century later, in 1892, while Scottish chemist Sir William Ramsay was working on scientific projects in the University College London’s lab, his curiosity was triggered by the work of the British physicist John William Strutt, 3rd Baron Rayleigh. Namely, Lord Rayleigh had noticed that the density of nitrogen separated from the air differs from the density of the chemical element eliminated from the compounds. At this point of realization, Sir William Ramsay started tracing the discovery path of a new chemical element of the periodic table, labeled as argon. 

By trying to trace argon in a uranium-bearing mineral, Sir William Ramsay discovered an element believed to exist only in the Sun – helium (He). Thanks to this discovery, Lord Rayleigh and Sir William Ramsay unraveled a whole new family of elements in the periodic table along the way, a family of elements labeled as noble gases. 

In 1894, these two University College London chemists managed to isolate this noble gas from the air. They did this by separating oxygen, carbon dioxide, water, and nitrogen from the air we breathe. Argon was the byproduct of nitrogen and oxygen production. In the first attempt, Sir William Ramsay followed the steps of Henry Cavendish by reproducing his experiment. Unlike Cavendish, Sir Ramsay applied spectroscopy in his scientific efforts, which brought him to the discovery of the new natural gas. 

Since both Sir William Ramsay and Lord Rayleigh happened to discover the new element almost at the same time, they agreed on sharing the great achievement and announced the first noble gas and a new element of the periodic table together. 

How Did Argon Get Its Name?

As a result of the indolence of the argon atoms, the name of this noble gas was derived from the Greek word “ἀργόν” (argon), meaning ‘the lazy one’. 

Where Can You Find Argon?

About 1% of the atmosphere of our planet Earth consists of argon. After oxygen and nitrogen, argon is the third natural gas that can be found abundantly in the air. Earth’s crust, as well as the ocean waters also contain small amounts of argon. In nature, most of the argon quantities are produced by radioactive decay, i.e. the decay of the radioactive isotopes of potassium-40 (40Ar).

Argon is isolated by the method of fractional distillation from liquid air. The same method is applied for the production of nitrogen, neon, xenon, oxygen, and krypton, in their purified forms. 

Where Is Argon Used in Everyday Life?

The Use of Argon in Industrial Processes and Production

This noble gas is used whenever an inert atmosphere is required. Examples of this use would be fire-suppression systems, light-bulbs, graphite electric furnaces, and the production of titanium (Ti). The incandescent and fluorescent light bulbs contain argon as a means to prevent oxygen corrosion of the hot filament. 

Furthermore, argon is used in various industrial processes (such as in the metal industry). More specifically, this chemical element is used as an inert shielding gas in arc-welding metals (stainless steel, aluminium). Also, the growth of germanium and silicon crystals requires an inert argon atmosphere.

The Use of Argon in Geochronology 

Argon is also applied in the practice of dating the Earth’s history. The origin of rocks, fossils, noble gases, and minerals can be determined by a method that uses argon, known as argon dating. Argon dating is a radiometric method for determining the origin of some structures or formations of the Earth by a single measurement of the argon isotopes. 

The Use of Argon In Medicine

Liquid argon is used in argon lasers as a substance and in surgery. The green-wave laser uses this gaseous substance in liquid form as an active medium, mostly used in ophthalmology. 

How Dangerous Is Argon?

Despite the fact that argon as a gas is not toxic, the density of this gaseous substance can lead to suffocation if inhaled. The symptoms of absorption of higher argon quantities by inhaling range from loss of consciousness, dizziness, and nausea to fatal consequences. 

Environmental Effects of Argon

Since argon is a gas that naturally exists in the atmosphere, it does not present any ecological threat to the environment.

Argon Isotopes

This chemical element with an atomic mass of 39.948 g.mol -1 has 26 isotopes (29Ar-54Ar), three of which are natural isotopes: 36Ar, 38Ar, 40Ar. There’s only one known isomer, the 32mAr. A half-life of 269 years makes 39Ar the radioactive argon isotope with the longest life. In contrast to the half-life of the aforementioned isotope, some argon isotopes have a half-life of only a few minutes. 

Iso­tope Decay
  abun­dance half-life (t1/2) mode pro­duct  
36Ar 0.334% stable
37Ar syn 35 d ε 37Cl  
38Ar 0.063% stable
39Ar trace 269 y β 39K  
40Ar 99.604% stable
41Ar syn 109.34 min β 41K  
42Ar syn 32.9 y β 42K  

Source: Wikipedia

Iso­topeDecay abun­dancehalf-life (t1/2)modepro­duct 36Ar0.334%stable37Arsyn35 dε37Cl 38Ar0.063%stable39Artrace269 yβ39K 40Ar99.604%stable41Arsyn109.34 minβ41K 42Arsyn32.9 yβ42K 
 abun­dancehalf-life (t1/2)modepro­duct 
37Arsyn35 dε37Cl 
39Artrace269 yβ39K 
41Arsyn109.34 minβ41K 
42Arsyn32.9 yβ42K 

Chemical Compounds of Argon

Argon compounds are not often encountered due to the inertness of its atoms. Some of the most important compounds of argon include argon fluorohydride (HArF) and aqueous argon. Also, argon binding molecules can appear in the form of diatomic, triatomic, and polyatomic van der Waals molecules. 

5 Interesting Facts And Explanations 

  1. The argon gas belongs to the family of noble gases in the table of elements that includes helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn), and oganesson (Og). Among them, only radon (Rn) has radioactive properties. 
  2. The term ‘London dispersion forces refers to a type of molecular force occurring between the molecules and atoms. This molecular action was discovered by Fritz London, a German chemist, after whom this chemical potency got its name. 
  3. The heat-insulating properties of argon make this chemical element suitable for inflation of the scuba-diving drysuits due to its low thermal conductivity. 
  4. Luxury cars have argon-insulated tires, which adds additional flair to the exhibition of affluence. 
  5. In 1904, Sir William Ramsay (1852–1916) won the Nobel Prize in chemistry for discovering the noble gas elements.