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Group 18 The Noble Gases

Noble gases have full valence electron shells. Valence electrons are the outermost electrons of an atom and are normally the only electrons which can participate in chemical bonding. According to atomic theory derived from quantum mechanics and experimental trends, atoms with full valence electron shells are extraordinarily stable and therefore do not form chemical bonds.

All of them exhibit an extremely low chemical reactivity and very few noble gas compounds have been prepared. No conventional compounds of helium or neon have yet been prepared, while xenon and krypton are known to show some reactivity in the laboratory. Recently argon compounds have also been successfully characterized. The noble gases' lack of reactivity can be explained in terms of them having a "complete valence shell". They have little tendency to gain or lose electrons. The noble gases have high ionization energies and negligible electronegativities. The noble gases have very weak inter-atomic forces of attraction, and consequently very low melting points and boiling points. This is why they are all monatomic gases under normal conditions, even those with larger atomic masses than many normally solid elements.




Helium, due to its non-reactivity (compared with flammable hydrogen) and lightness, is often used in blimps and balloons. Helium and Argon are very commonly used to shield a welding arc, and the surrounding base metal from the atmosphere during welding.

Also there is a video on superfluid helium.


Hindenberg disaster
Hindenburg Disaster (hydrogen filled)
Helium Filled


  Neon is the second-lightest noble gas. It glows reddish-orange in a vacuum discharge tube.


  Argon is often used as a suitable safe and inert atmosphere for the inside of filament light bulbs, and is also used as an inert atmosphere in the synthesis of air and moisture sensitive compounds (as an alternative for nitrogen). Helium and Argon are very commonly used to shield a welding arc, and the surrounding base metal from the atmosphere during welding.

 Preparation of liquid and solid argon

Argon gas liquefied by cooling in liquid nitrogen and than freezing.
Boiling point of liquid Nitrogen is -195.79 C
Boiling point of liquid Argon is −185.85 C
Freezing point of Argon is −189.35 C



  Krypton is also used in lasers, which are used by doctors for eye surgery.

Does react with Fluorine.


  Xenon is a very dense Noble Gas. Xenon is a Noble gas that can for compounds.


  Radon is radioactive. Formed from the decomposition of radium.

Radon being a dense gas accumulates in low laying areas where granite is present. Breathing it in can cause lung cancer.

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