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Argon

What is argon?

Argon is a chemical element or inert or noble gas of Group 18 of the periodic table with the symbol Ar and atomic number 18. It is the most abundant noble gas which is used widely in metallurgy and other industry due to its cheap price. Due to the filled valence shell orbital, the oxidation number or state of argon is zero and the ionization energy is very high.

Argon (Ar), chemical element, noble gas of Group 18 of periodic table with properties, uses in metallurgy or fluorescent tube

It is a colorless, odorless, tasteless, monoatomic gas that occurs to the extent of 93 ppm by volume in dry air and 4 × 10−2 ppm by weight in igneous rocks.

The name of the lighter gas, argon derived from the Greek latter Argos meaning idle. In solid-state, it forms a face-centered cubic crystal lattice.

Argon on the periodic table

Argon is placed in the p-block of the periodic table with other noble gases like helium, neon, krypton, xenon, and radon.

Position of noble gas or inert gas argon on the periodic table elements

Argon discovery

It was discovered nearly one hundred years after the English natural philosopher and scientist Henry Candavis’s observation. He observed that a sample of air always leaves a small residue of about 1/120 part of inert gases after repeated sparking with air oxygen.

British scientist Lord Rayleigh observed that nitrogen isolated from atmospheric gases was about 0.5 percent heavier than nitrogen prepared chemically. He identified a new element (argon = idle) in the residue left after heating atmospheric nitrogen with magnesium.

Sir William Ramsay suggested that helium and argon belong to the new group (group zero) in the periodic table.

When the residual gas was subjected to spectroscopic analysis, a new characteristic electromagnetic spectrum was obtained. British scientist Lord Rayleigh was awarded the Noble Prize in physics for the investigation of gas density and the discovery of argon.

Sir William Ramsay gets a noble prize in chemistry for the discovery of inert gas in the air and its place on the periodic table.

Isotopes

It is the most abundant noble gas in air, 93 ppm by dry air, in igneous rocks it is present to the extent of 4 × 10−2 by weight.

Natural argon is a mixture of isotopes like 40Ar (99.6 percent), 36Ar (0.063 percent), and 36Ar (0.337 percent). 40Ar prepared by nuclear reaction or electron capture reaction of 40K.

Properties of argon

The most abundant inert gas, Ar has a valence shell electron configuration [Ne] 3s2 3p6, and a heat capacity ratio (Cp/Cv) close to 1.66.

Argon
Symbol Ar
Discovery Lord Rayleigh and Sir William Ramsay in 1894
Name derived from The Greek word argos means idle
Common isotope 18Ar40
Oxidation states 0
CAS number 7440-37-1
Periodic properties
Atomic number 18
Relative atomic mass 39.948
Electron per cell 2, 8, 8
Electronic Configuration [Ne] 3s2 3p6
Block p-block
Group 18
Period 3
Physical properties
State at 20 °C Gas
Melting point −189.34 °C, −308.81 °F, 83.81 K
Boiling point −185.85°C, −302.53°F, 87.30 K
Molar heat capacity 20.85 J mol−1 K1
Crystal structure face-centered cubic (fcc)
Density 0.001633 g/cm3
Critical temperature 150.69 K
Atomic properties
Atomic radius (non-bonded) 1.88 Å
Covalent radius 1.01 Å
Electronegativity unknown
Electron affinity unknown
Ionization energy (kJ/mol) 1st 2nd 3rd
1520.57 2665.86 3930.81

Facts about argon

The chemistry of argon or other noble gases is different from other elements of the periodic table due to their filled valence shell configuration.

The promotion of electrons to the next available orbitals needs very large energy. The facts suggest that the covalent bonding in Ar is highly unfavorable.

The ionic compounds with the most electronegative fluorine are unlikely due to high positive entropy and free energy for the formation of such a chemical bonding. Therefore, no true chemical compounds of Ar are known.

Chemical compounds

The only clathrates or cage compounds of argon formed with para quinol and water. The noble gas molecule is trapped within the cavities formed by quinol crystal through a hydrogen bonding network.

Water and zeolite also produce such types of clathrates compounds with Ar molecule. These compounds are not called true chemical compounds since weak Van der Waals forces operate between the gas molecule and quinol or water.

What is argon used for?

Argon element tube or lamp, sign, uses and properties

  • Argon is the most abundant and cheapest noble gas mainly obtained on a large scale by fractional distillation of air. It is used to protect metal surfaces from oxidation during the welding of steel, aluminum, and magnesium.
  • It is widely used in electrical equipment like filament bulbs and radio tubes.
  • We used argon gas in different types of industrial production processes, scientific research, and medicine.
  • Argon atmosphere is used in some high-temperature industrial processes, for the production of metals like titanium, vanadium, zirconium, uranium, etc.
  • The non-toxic argon is also used for packing food materials to extend the food life.
  • We also used it for the preservation and packaging of chemicals like varnish, polyurethane, and paint.
  • It is used for thermal insulation in energy-efficient windows.
  • The blue argon laser is used in medicine to destroy the tumors of the human body.