Noble gas

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Helium spectrum

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First Ionization Energy blocks

Electron shell 010 Neon - no label

Xenon-tetrafluoride-3D-vdW

Endohedral fullerene

XeF2

Noble gases are a group of chemical elements with similar properties; under standard conditions, they are all odorless, colorless, monatomic gases with very low chemical reactivity. The six naturally occurring noble gases are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and the radioactive radon (Rn). In the periodic table, they occupy the rightmost column, known as Group 18 or the noble gases group. The term "noble gas" is derived from the German word 'Edelgas', for "noble" or "inert", reflecting their resistance to forming compounds. A seventh element, oganesson (Og), is a synthetic element that is classified as a noble gas in the periodic table, although its chemical properties have not been thoroughly investigated due to its extreme radioactivity and short half-life.

Properties

Noble gases are characterized by their high ionization energies and negligible electronegativities. They are all gases at room temperature and exhibit a low chemical reactivity due to their full valence electron shell. This makes them very stable and unlikely to form chemical compounds. However, under extreme conditions, noble gases can form compounds with highly reactive elements. For example, xenon can form compounds with fluorine and oxygen, such as xenon hexafluoride (XeF6) and xenon trioxide (XeO3).

Occurrence

Noble gases are relatively rare in the Earth's atmosphere, with argon being the exception; it makes up about 0.934% of the atmosphere due to the decay of potassium-40 into argon-40. Helium, produced by the radioactive decay of elements within the Earth's crust, is trapped in natural gas reserves and is the only noble gas produced commercially by extraction from natural sources. Other noble gases are obtained through the fractional distillation of air.

Applications

Noble gases have various applications due to their unique properties. Helium is used in cryogenics, for cooling superconducting magnets in MRI machines, and as a lifting gas in balloons and airships. Neon is famous for its use in advertising signs, while argon is used as an inert gas shield for arc welding and in the production of titanium and other reactive elements. Krypton, xenon, and radon have specialized uses in lighting, medical imaging, and radiation therapy, respectively.

History

The discovery of noble gases dates back to the late 19th century when scientists began to study the components of the Earth's atmosphere. Argon was the first noble gas to be discovered in 1894 by Lord Rayleigh and Sir William Ramsay. This discovery challenged the existing periodic table, leading to the addition of a new group to accommodate these elements. Subsequently, the other noble gases were identified: helium in 1895, neon, krypton, and xenon in 1898, and finally, radon in 1900 by Friedrich Ernst Dorn.

Environmental and Safety Considerations

Noble gases are non-toxic and non-flammable, making them safe for a variety of uses. However, their asphyxiant properties can pose a risk in high concentrations, displacing oxygen in the air and creating a suffocation hazard. Radon, being radioactive, presents a health risk if inhaled, as it can cause lung cancer over prolonged exposure.

See Also

• Periodic table
• Inert gas
• Chemical element
• Gas