Why are Group 18 elements called 'noble gases'?

Group 18 elements are termed 'noble gases' due to their extreme chemical inertness, much like royalty or nobility who historically did not mix with commoners. This inertness arises from their stable electronic configuration, specifically a completely filled valence shell with eight electrons (an octet), except for Helium ($1s^2$). This stable configuration means they have very little tendency to gain, lose, or share electrons to form chemical bonds under normal conditions, making them highly unreactive and 'noble' in their behavior.

What is the primary source of Helium, and why is it not primarily extracted from the atmosphere?

While Helium is present in the atmosphere, its concentration is extremely low (about 0.0005% by volume). The primary commercial source of Helium is natural gas deposits. Helium is formed underground from the alpha decay of radioactive elements like uranium and thorium. These alpha particles, which are essentially Helium nuclei, capture electrons to become neutral Helium atoms, accumulating in natural gas reservoirs. Extracting Helium from natural gas is far more economically viable and efficient than from the atmosphere due to its higher concentration in these deposits.

How are noble gases like Argon, Neon, Krypton, and Xenon obtained from the atmosphere?

These noble gases are obtained through the fractional distillation of liquid air. Air is first cooled to a very low temperature (around $-200^circ ext{C}$) and compressed, causing it to liquefy. The liquid air, which is a mixture of nitrogen, oxygen, and noble gases, is then slowly warmed. Each component has a distinct boiling point: nitrogen boils at $-196^circ ext{C}$, argon at $-186^circ ext{C}$, and oxygen at $-183^circ ext{C}$. By carefully controlling the temperature, these components vaporize at different stages and can be collected separately. Neon, Krypton, and Xenon are present in even smaller quantities and are separated in subsequent distillation steps.

Why is Helium preferred over Hydrogen for filling balloons and airships, despite Hydrogen being lighter?

Helium is preferred over Hydrogen for filling balloons and airships primarily because Helium is non-flammable, whereas Hydrogen is highly flammable and forms explosive mixtures with air. Although Hydrogen is slightly lighter than Helium, the safety advantage of Helium far outweighs this minor difference in lift. The Hindenburg disaster in 1937, caused by the ignition of hydrogen, tragically demonstrated the dangers of using flammable gases in airships, solidifying Helium's role as the safer choice.

Can noble gases form compounds? If so, which ones and under what conditions?

While noble gases are largely inert, the heavier noble gases, particularly Xenon and Krypton, can form compounds under specific, often extreme, conditions. The first noble gas compound, Xenon hexafluoroplatinate ($XePtF_6$), was synthesized in 1962. Since then, numerous compounds of Xenon with highly electronegative elements like fluorine and oxygen have been prepared, such as $XeF_2$, $XeF_4$, $XeF_6$, $XeO_3$, and $XeO_4$. Krypton also forms a few compounds, like $KrF_2$. Radon, being radioactive, is difficult to study but is also known to form fluorides. Helium, Neon, and Argon are generally considered to be completely unreactive chemically.

What is the role of Argon in welding processes?

Argon plays a crucial role in various welding processes, particularly in TIG (Tungsten Inert Gas) and MIG (Metal Inert Gas) welding. Its primary function is to create an inert atmosphere around the welding arc and the molten metal pool. At high temperatures, metals can react with oxygen and nitrogen from the air, leading to oxidation, nitridation, and embrittlement of the weld. Argon, being unreactive, shields the weld area, preventing these undesirable reactions and ensuring a strong, clean, and high-quality weld. Its relatively high density also helps in effectively displacing air from the welding zone.

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Version 1Updated 22 Mar 2026

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Group 18 elements, commonly known as noble gases, are a unique family in the periodic table characterized by their exceptional chemical inertness under normal conditions. This inertness stems from their completely filled valence electron shells, specifically an $ns^2np^6$ configuration (except for Helium, which has $1s^2$ ). Their occurrence in nature is primarily in the Earth's atmosphere, albeit …

Quick Summary

Group 18 elements, known as noble gases (He, Ne, Ar, Kr, Xe, Rn), are characterized by their exceptional chemical inertness due to a stable, completely filled valence electron shell ( $ns^2np^6$ or $1s^2$ for He).

Their occurrence is primarily in the Earth's atmosphere in trace amounts, with Argon being the most abundant noble gas in air. Helium is also significantly found in natural gas deposits, a product of radioactive decay.

Radon is a radioactive decay product of radium, found in rocks and soil. Extraction of most noble gases (Ne, Ar, Kr, Xe) involves fractional distillation of liquid air, while Helium is separated from natural gas.

Their uses are diverse and stem from their inertness, low density, and unique spectral properties. Helium is used in cryogenics (MRI), balloons, and diving mixtures. Neon creates the iconic red-orange glow in advertising signs.

Argon is widely used to provide inert atmospheres in welding and in incandescent light bulbs. Krypton and Xenon find applications in specialized high-intensity lamps and lasers. Xenon also has anesthetic properties and is used in ion propulsion.

Radon has limited medical uses in radiotherapy. Understanding these specific applications and their underlying properties is crucial for NEET.

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He: — Natural gas, Cryogenics (MRI, NMR), Balloons, Diving (Heliox).

Ne: — Liquid air, Neon signs (red-orange light), Indicator lamps.

Ar: — Liquid air, Most abundant in air, Welding (inert atmosphere), Incandescent bulbs.

Kr: — Liquid air, High-performance lamps, Lasers.

Xe: — Liquid air, HID lamps (car headlights), Anesthesia, Ion thrusters.

Rn: — Radioactive decay of Radium, Radiotherapy (limited).

General: — All are monatomic, colorless, odorless, tasteless gases. Inert due to

ns^2np^6

configuration (He

1s^2

). Heavier noble gases (Xe, Kr) can form compounds with F, O.

He-Ne-Ar-Kr-Xe-Rn: Heavy Noble Atoms Keep Xenon Reacting Nicely.

Uses Mnemonic:

He: Health (MRI), Heavy (diving), Hot (cryo), High (balloons) Ne: Neon Nice Nights (signs) Ar: Arc Atmosphere Argon (welding, bulbs) Kr: Kool Krypton Keeps Kars Klearly Keeping (high-performance lamps, car lights) Xe: Xenon X-ray Xtra Xtra (anesthesia, HID lamps, ion thrusters) Rn: Radioactive Radon Radiation (radiotherapy)

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