Argon (Ar): Uses, Chemical & Physical Properties

Overview

Argon is a chemical element with the symbol (Ar) and atomic number 18. It is in group 18 of the periodic table together with Helium (He), Neon (Ne), Krypton (Kr), Xenon (Xe) and Radon (Rn). They are generally categorized as noble gases.

Argon is colorless, odorless, tasteless, nontoxic and nonflammable gas. It is chemically inert under most conditions and forms no confirmed stable compounds at room temperature. However, under various extreme conditions, argon can form some compounds. For example Argon can react with fluorine under extreme conditions to form Argon fluorohydride (HArF).

Argon has approximately the same solubility in water as oxygen and is 2.5 times more soluble in water than nitrogen. Argon is produced industrially by the fractional distillation of liquid air and is mostly used as an inert shielding gas in welding and other high-temperature industrial processes where ordinarily unreactive substances become reactive.

What You Need To Know About Argon

Discovery

Argon was discovered by an English chemist Lord Rayleigh and a Scottish chemist Sir William Ramsay in 1894 at University College London. Argon was discovered as a result of trying to explain why the density of nitrogen extracted from air differed from that obtained by the decomposition of ammonia.  It was isolated by examination of the residue obtained by removing nitrogen, oxygen, carbon dioxide and water from clean air. The examination entailed a carefully designed sequence of experiments guided by an analysis of the resulting observation.

Sir William Ramsay and Lord Rayleigh collaborated in isolating Argon from air. They removed all the nitrogen from the gas they had extracted from air and did this by reaching it with hot magnesium, forming the solid magnesium nitride. They were then left with a gas that would not react and when they examined its spectrum they saw new groups of red and green lines, confirming that it was a new element.

Occurrence In Nature  

Argon makes up 0.93% of the earth’s atmosphere, making it the third most abundant atmospheric gas. On Earth, the vast majority of argon is the isotope argon-40 which arises from the radioactive decay of potassium-40. Argon is obtained from the air as a byproduct of the production of oxygen and nitrogen.

Periodic Table Facts

• The atomic symbol of Argon is Ar.
• In the periodic table, Argon is located in group 18 (noble gases), period 3, p-block. 
• Cobalt is categorized as a noble gas in the periodic table. Other elements in the same category include: helium, neon, argon, krypton, xenon and radon.
• The atomic number of cobalt is 18. Atomic number is the number of protons.
• Argon has an electron configuration of (Ne)3s²3p⁶
• Electrons per shell in Argon is 2,8,8. The outermost (valence) shell of argon has eight electrons, making it exceedingly stable and thus chemically inert.  

Physical Properties

• Argon is a colorless, odorless gas that is totally inert to other substances.
• Argon is denser than air.
• Argon has approximately the same solubility as oxygen and it is 2.5 times as soluble in water as nitrogen.
• Argon is chemically inert under most conditions and forms no confirmed stable compounds at room temperature.
• Argon is a gas at standard temperature and pressure.
• Argon gas condenses to a colorless liquid at -185.8^oC (-302.4^oF) and to a crystalline solid at -189.4^oF (-308.9^oF).
• The melting point of Argon is 83.81K (-308.81^oF, -189.34^oC).
• Boiling point of Argon is -185.848^oC (87.302K, -302.526^oF).
• Density of argon at standard temperature and pressure is 0.0017837 grams per cubic centimeter (1.78g/L).
• The triple point of argon is 83.8058K, 68.89 kPa.
• The critical point of argon 150.687K, 4.863 Mpa.
• The heat of fusion of argon is 1.18 kJ/mol.
• The heat of vaporization of argon is 6.53 kJ/mol.
• Argon has a Molar heat capacity of 20.85 kJ/mol.

Other Properties

• According to Royal Society of Chemistry (RSC) Argon makes up 0.94 percent of Earth’s atmosphere and is the third most abundant atmospheric gas.
• The electrical resistivity of argon is very low.
• Thermal conductivity of Argon is 17.72 x 10^-3 W/(m.k).
• Argon is diamagnetic at standard pressure and temperature.
• The main isotopes of argon found on Earth are ⁴⁰Ar(99.6%), ³⁶Ar(0.34%) and ³⁸Ar(0.06%).
• Argon atoms do not combine with one another nor have they been observed to combine chemically with atoms of any other element.
• The atomic weight of argon is 39.948. Atomic weight is the average mass of the atom.
• The electronegativity of argon is unknown.
• The first, second and third Ionization energies of argon is 1520.6 kJ/mol, 2665.8 kJ/mol and 3931 kJ/mol respectively.
• The Van der  waals radius of argon is 188 pm.
• Argon has a face-centered cubic crystal structure.

Production

• Argon is obtained from the air as a byproduct of the production of oxygen and nitrogen.
• Argon is produced commercially by fractional distillation of liquefied air with (for high purity argon) catalytic burning of left over traces of oxygen.
• On earth the vast majority of argon is the isotope argon-40, which arises from the radioactive decay of potassium-40.

Uses Of Argon

• Argon is used in some types of arc welding such as gas metal arc welding and gas tungsten arc welding as well as processes that require shielding from other atmospheric gases.
• Argon is used in radio tubes and Geiger counters.
• Argon is also used in technical SCUBA diving to inflate the drysuit due to its nonreactive, heat isolating effect.
• Argon is used in incandescent light bulbs to stop oxygen from corroding the filament.
• The most exotic use of argon is in the tyre of luxury cars to protect the rubber and reduce road noise.
• Cryosurgery procedures such as cryoablation use liquid argon to destroy tissue such as cancer cells.
• Argon is used as a non-reactive blanket in the production of titanium and other reactive elements and as a protective atmosphere for glowing silicon and germanium crystals.
• Argon-39 is used for ground water dating.
• Argon has low thermal conductivity and is used as the gas between the glass panes in high-efficiency double and triple glazing.
• Argon is used in medical lasers, in ophthalmology for example to correct eye defects such as blood vessel leakage, retinal detachment, glaucoma and macular degeneration.
• Liquid argon is used as the target for neutrino experiments and direct dark matter searches.
• Argon is also used to displace oxygen and moisture-containing air in packaging material to extend the shelf-lives of the contents.
• Argon is sometimes used as the propellant in aerosol cans for such products as varnish, polyurethane and paint and to displace air when preparing a container for storage after opening.
• Argon may be used as the carrier gas in gas chromatography and in electrospray ionization mass spectrometry. It is also the gas of choice for the plasma used in ICP spectroscopy.
• Argon is the preference gas for sputter coating of specimens for scanning electron microscopy.

Summary Of Properties Of Argon In Tabular Form