Noble gas
Encyclopedia : N : NO : NOB : Noble gas
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- For the musical band, see Noble Gas (band)
Etymology
The noble gases were previously referred to as inert gases, but this term is not strictly accurate because several of them do take part in chemical reactions. Another older term was rare gases, although in fact argon forms a considerable part (0.93% by volume, 1.29% by mass) of the Earth's atmosphere.The name 'noble gases' is an allusion to the similarly unreactive Noble metals, so called due to their preciousness, resistance to corrosion and long association with the aristocracy.
| Noble gases | atomic number in red are gases | solid borders are primordial elements (older than the Earth) | dashed borders are naturally radioactive elements | dotted borders are radioactive, synthetic elements | those without borders have not been discovered yet |
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Chemistry
Under standard conditions, the noble gasses all occur as monatomic gases.
All of them exihibit an extremely low chemical reactivity, in fact no conventional compounds of helium or neon have yet been prepared. Xenon and krypton are known to show some reactivity in the laboratory—see noble gas compounds . Recently argon compounds have also been successfully characterised.
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.
Because of their unreactivity, the noble gases were not discovered until 1868, when helium was detected spectrographically in the Sun. The isolation of helium on Earth had to wait until 1895. 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 gases under normal conditions, even those with larger atomic masses than many normally solid elements.
Ununoctium
No isotopes with 118 protons have yet been detected in nature or synthesized in the laboratory. In the meantime, the systematic name "ununoctium" is used to refer to this hypothetical element. If discovered, ununoctium is expected to be another noble gas, filling the empty space in the periodic table beneath radon. All its isotopes are likely to be radioactive with a very short half-life in the millisecond range.
Applications
One of the most commonly encountered uses of the noble gases in everyday life is in lighting. 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). Some of the noble gases glow distinctive colours when used inside lighting tubes (neon lights). Helium, due to its unreactivity (compared to flammable hydrogen) and lightness, is often used in blimps and balloons.Physical Properties
| align = center | Property
|- | align = center | Element Number | align = center | 2 | align = center | 10 | align = center | 18 | align = center | 36 | align = center | 54 | align = center | 86 | align = center | 118 |- | align = center | Element Name | align = center | Helium | align = center | Neon | align = center | Argon | align = center | Krypton | align = center | Xenon | align = center | Radon | align = center | Ununoctium |- | align = center | Normal Density | align = center | 0.1786 | align = center | 0.9002 | align = center | 1.7818 | align = center | 3.708 | align = center | 5.851 | align = center | 9.97 | align = center | N/A |- | align = center | Atomic Mass | align = center | 4.00 | align = center | 20.2 | align = center | 39.9 | align = center | 82.92 | align = center | 130.2 | align = center | 222.4 | align = center | N/A |- | align = center | Boiling Pt. (°C) | align = center | -268.83 | align = center | -245.92 | align = center | -185.81 | align = center | -151.7 | align = center | -106.6 | align = center | -62 | align = center | N/A |- | align = center | Melting Pt. (°C) | align = center | -272 | align = center | -248.52 | align = center | -189.6 | align = center | -157 | align = center | -111.5 | align = center | -71 | align = center | N/A
External links
- Ohio State University [press release] for uranium compounds with noble gases.
- [Rare Gases - Neon, Krypton, Xenon Properties, Uses, Applications]
- [Argon Ar Properties, Uses, Applications]
- [Science Aid: Noble gases] Simple look at the properties and uses of noble gases
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