Argon Element in Periodic Table
Argon (Ar), chemical element, inert gas, or noble gas of Group 18 of the periodic table is the most abundant gases used widely in metallurgy and other industry due to its cheap price. It is a colorless, odorless, tasteless, monoatomic gas, 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 lazy. In solid-state, it forms a face-centered cubic crystal lattice.
The most abundant inert gas, argon has the chemical symbol Ar, atomic number 18, atomic weight 39.948, melting point -189.34 °C, boiling point -185.85 °C, valence shell electron configuration [Ne] 3s2 3p6, and heat capacity ratio (Cp/Cv) close to 1.66. Due to filled valence orbital, the oxidation number or state is zero and the ionization energy of argon is very high.
History and Occurrence
Argon was discovered nearly one hundred years after the English natural philosopher and scientist Henry Candavis observation. He observed that a sample of air always leaves a small residue 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 = lazy) 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 awarded the Noble Prize in physics for investigation of gas density and discovery of argon. Sir William Ramsay gets a noble prize in chemistry for the discovery of inert gas in the air and their place in the periodic table. 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. The 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.
Chemistry of Noble Gases
The chemistry of argon or other noble gases like helium, neon, argon, krypton, xenon, and radon 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 is very large. 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.
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 form 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.
Uses of Argon
Argon is the most abundant and cheapest noble gases mainly obtained on a large scale by fractional distillation of air. It is used to protect the metal surfaces from oxidation during the welding of steel, aluminum, and magnesium. The chemical element argon is widely used in electrical equipment like filament bulbs, radio tubes, in different types of the industrial production process, 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, for the preservation and packaging of chemicals like varnish, polyurethane, and paint, for thermal insulation in energy-efficient windows. The blue argon laser is used in medicine to destroy the tumors of the human body.