The World Of Noble Gases
Noble Gases are chemical elements that make up the Group 18, the far-right column, in the periodic table. These elements share a range of properties – they are all colorless, odorless, tasteless and nonflammable gases – and most importantly, they are highly reluctant to undergo a chemical reaction. It is because of their low chemical reactivity that they are called noble gases and six of the naturally occurring noble gases are Helium, Neon, Argon, Krypton, Xenon and Radon.
The Noble gases were conventionally called as inert gases, but this term had to be changed as these gases are not entirely inert. It was initially thought that they could not combine with other elements to form chemical compounds, but the fact is that even when they have a very low inclination to undertake a chemical reaction, it is observed that chemical compounds of some noble gases do exist.
So what makes the noble gases halfhearted towards chemical reactions? Well, these elements have the maximum number of valence electrons - an electron of an atom, located in the outermost shell or valence shell of the atom, that can participate in the formation of a chemical bond - and this stability offered by the completeness of the outer shell makes them highly unenthusiastic to react with other elements. In chemistry the term noble was traditionally associated with metals like platinum, gold and iridium, which are resistant to corrosion and oxidation, and which have a reluctance to chemically react. So it was natural that gases, which showed similar unwillingness to chemically react, were called noble gases. The term was coined - Edelgas in German- by the German chemist, Hugo Erdmann in 1898.
Noble gases are utilized for a range of industrial purposes and they are commercially obtained through various methods. They are all found in the Earth’s atmosphere and noble gases like Argon, Krypton, Neon and Xenon are acquired using liquefaction – a physical conversion of a gas into a liquid state - and fractional distillation - separation of a mixture into its component parts - processes. Helium is obtained by separating it from natural gas and Radon is attained by isolating it from the radioactive decomposition of radium compounds.
The history of Noble Gases
Henry Cavendish as illustrated in the frontispiece of A The life of the Hon. Henry Cavendish by George Wilson, published in 1851.
In 1784, the British scientist, Henry Cavendish, found that when all the known atmospheric gases were chemically removed from a sample of air, a very small percentage of an unknown substance remained. Cavendish was unable to identify this substance, which was chemically less reactive than nitrogen – a gas that was already discovered and isolated and found to be inert.
In 1895, Lord Rayleigh (John William Strutt), a British physicist, while researching on the densities of the gases in the air, came across similar observations as Cavendish. He perceived that nitrogen found in the atmosphere were denser than nitrogen produced from chemical reactions and theorized the presence of a previously unidentified gas in the nitrogen produced from chemical reactions. Together with the British chemist William Ramsay, Rayleigh pursued this mystery gas and in 1894, they succeeded in isolating this new element, which they named argon - derived from the Greek word meaning idle or lazy.
Sir William Ramsay & Lord Rayleigh. Portraits taken from Les Prix Nobel, 1904, the annual yearbook by the Nobel Foundation.
Ramsay carried on with his researches and soon isolated helium, while experimenting with cleveite, an impure radioactive mineral consisting mainly of uranium dioxide. Helium, as an element was initially identified spectroscopically in the Sun in 1868, but it was yet to be detected on Earth. Ramsay’s experiment with cleveite in 1895 resulted in the first terrestrial isolation of helium. In 1898, Ramsay along with the English chemist, Morris Travers discovered xenon, neon and krypton. In 1904, Lord Rayleigh and William Ramsay received the Nobel Prize in Physics and in Chemistry, respectively for their works associated with the noble gases.
In 1900, the German physicist Friedrich Ernst Dorn, while studying the decay chain of radium, noticed that radium compounds emanated a radioactive gas. This gas, which was initially named as Radium Emanation, was added to the noble gas group in 1904 and was named Radon in 1923. The discovery of the noble gases and their reluctance to chemically react contributed appreciably to the advance of theories related to the atomic structure.
Helium – The lightest and most abundant member of noble gases group
Helium, the chemical element with the symbol He and atomic number 2 is the first element in the noble gas group in the periodic table. Named after the Greek god of the Sun, Helios, it is the second lightest and second most abundant element in the universe, after hydrogen.
The most common use of Helium is in the field of cryogenic - the study of the production and behavior of materials at very low temperatures - applications, like the use of liquid helium for cooling the superconductor magnets in modern MRI scanners. Because of its inertness, it is also used mainly to create protective shields or controlled environments in applications like gas chromatography. It is also used to create a shield environment in cutting and arc welding processes.
Helium is used as a component for breathing gases due to its low solubility in fluids. A breathing gas of helium and oxygen mixture is used by deep-sea divers, as a preventive measure against oxygen, nitrogen and carbon dioxide toxicity effects. Since it is much less denser than air and incombustible, Helium is used in balloons and airships as a safe lifting gas.
Because of the highly flammable nature of Hydrogen, Helium is now used as the safe lifting gas for lighter-than-air aircrafts.
Neon – The shining star of the advertisement industry
Neon, is a chemical element with the symbol Ne and atomic number 10. The name of the element is derived from the Greek word for new.
Neon is used in a range of lighting applications like neon lights, advertising signs, luminous warnings, lasers and television tubes. Its most popular application is the neon tubing used in the field of advertising. When noble gases are confined in a glass tube at low pressure, an electrical discharge to the tube will make the gas glow and emit bright light. When ionized, neon produces a bright reddish-orange light and different colors are achieved by coating the inside of the glass tube with other chemicals. It is also used as a cryogenic refrigerant in some commercial applications.
Argon – The first noble gas that was discovered
Argon, the chemical element with the symbol Ar and atomic number 18, is the third most abundant gas in the Earth’s atmosphere. Since argon is inexpensive, it has many uses in the lighting & electronics industry and is also used in creating inert gas atmosphere for cutting and welding applications like gas metal arc welding.
Argon is used in many of the high-temperature industrial processes to provide a non-reactive environment. It is used to create an oxygen and nitrogen free environment while annealing metals. Argon is used in incandescent light bulbs for preventing the burning up of the thin filaments due to oxidation. Argon filled gas discharge lamps produce a bluish light when ionized. Argon is also used by window manufacturers as a thermal insulation while creating energy-efficient windows, because of its low thermal conductivity.
Krypton, Xenon and Radon – The other members of the noble gases
Krypton - symbol Kr and atomic number 36 -, Xenon - symbol Xe and atomic number 54 - and Radon - symbol Rn and atomic number 86 – are other members of the noble gases group. Krypton is used mainly in high performance light bulbs, headlights, lasers and photographic flash bulbs. It is also used as a thermal insulation in energy-efficient windows.
Xenon is commonly used in gas-discharge lamps, in high-intensity automotive headlamps, x-ray development and in lasers. It is also used in the medical field as a general anesthetic. Radon, which is radioactive, is used in radiation therapy to treat cancer and to treat arthritis.
Is there a seventh member in the Group 18?
Oganesson, a chemical element with symbol Og and atomic number 118, which was first synthesized in 2002 and which was formally named on 28 November 2016, is now a member of the group 18 and is predicted as a noble gas. Since this radioactive element is very unstable, no conclusive classification of its chemical properties are attained and the classifications are based on predictions formed on theoretical calculations.
Oganesson has the highest atomic number and highest atomic mass of all known elements and is named after the Russian nuclear physicist, Yuri Oganessian, for his contributions to the discovery of the heaviest elements in the periodic table.