Noble gas

Noble gas
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This article is about the chemical series. For other uses, see Noble gas (disambiguation).
Group 18
Period
1 2
He
2 10
Ne
3 18
Ar
4 36
Kr
5 54
Xe
6 86
Rn
7 118
Uuo


Neon, like all noble gases, has a "full" valence (outermost) electron shell.
The noble gases are the elements in group 18 (also sometimes Group 0 IUPAC Style, or Group 18) of the periodic table. It is also called helium family or neon family. Chemically, they are very stable due to having the maximum number of valence electrons their outer shell can hold. A thorough explanation requires an understanding of electronic configuration, with references to quantum mechanics. Noble gases rarely react with other elements since they are already stable. Under normal conditions, they occur as odorless, colorless, monatomic gases. Each of them has its melting and boiling point close together, so that only a small temperature range exists for each noble gas in which it is a liquid. Noble gases have numerous important applications in lighting, welding and space technology.




Contents [hide]
1 Etymology
2 History
3 Chemical makeup
4 Applications
5 Physical properties
6 Notation
7 References
8 External links



[edit] Etymology
"Noble gas" is the translation of the German Edelgas, which was in use as early as 1898[1]. The term edelgas is literally translated as immaculate gas. This refers to the extremely low level of reactivity under normal conditions. The noble gases have also been referred to as inert gases, but these terms are not strictly accurate because several of them do take part in chemical reactions. Another old term is rare gases, although in fact argon forms a considerable part (0.93% by volume, 1.29% by mass) of the Earth's atmosphere.[2]


[edit] History
The existence of noble gases was not known until after the advent of the periodic table. In the late nineteenth century, Lord Rayleigh discovered that some samples of nitrogen from the air were of a different density than nitrogen resulting from chemical reactions. He and William Ramsay theorized that the nitrogen extracted from air was associated with another gas, argon. With this discovery, they realized that a whole class of gases was missing from the periodic table. Eventually all the known noble gases except for helium were discovered in the air, with argon being much more common than the others, and the table was completed. Helium was detected spectrographically in the Sun in 1868. The isolation of helium on Earth had to wait until 1895. Under standard conditions, the noble gases all occur as monatomic gases.[3] In 1897 there was evidence that argon and helium were part of a new column on the periodic table. This column was completed in the early 1900s with the discovery of the final naturally occurring elements. [4]


[edit] Chemical makeup
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.[5]

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 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. 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.


[edit] 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 colors when used inside lighting tubes (neon lights). Helium, due to its nonreactivity (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. Krypton is also used in lasers, which are used by doctors for eye surgery.[6]


[edit] Physical properties
Property Noble gas
Element number 2 10 18 36 54 86
Element name Helium Neon Argon Krypton Xenon Radon
Density (g/dm3) 0.1786 0.9002 1.7818 3.708 5.851 9.97
Atomic radius (nm) 0.050 0.070 0.094 0.109 0.130 -
Boiling point (°C) -268.83 -245.92 -185.81 -151.7 -106.6 -62
Melting point (°C) -272 -248.52 -189.6 -157 -111.5 -71


[edit] Notation
The Noble Gases can be used in conjunction with the electron configuration notation to make what is called the Noble Gas Notation. For example: The element carbon would be 1s22s2 2p2 would be [He] 2s22p2.

This notation makes the identification of elements faster, and is shorter and easier than writing out the full notation of orbitals.


[edit] References
^ Erdmann, H Lehrbuch der Anorganischen Chemie (1898), page 84, cited in Science 15 February 1901 13: 268-270, by Edward Renouf.
^ Periodic Table: Noble Gases. Retrieved on 2007-03-11.
^ Cosmic Chemistry: An Elemental Question (English) 7. NASA: Jet Propulsion Laboratory. Retrieved on 2007-03-11.
^ Ozima, Minoru; Podosek, Frank A. (2001). Noble Gas Geochemistry (English) 2. Cambridge University Press. Retrieved on 2007-03-14.
^ Carpi, Anthony. Chemical Reactions (English). Visionlearning. Retrieved on 2007-03-11.
^ Inspiring Gases: Noble Gases. Retrieved on 2007-03-11.

[edit] 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
Open University video demonstrating noble gases differing densities
[hide]v • d • ePeriodic tables
Layouts Standard · Vertical · Full names · Names and atomic masses · Text for last · Huge table · Metals and nonmetals · Blocks · Valences · Inline f-block · 218 elements · Electron configurations · Atomic masses · Electronegativities · Alternatives
Lists of elements Name · Atomic symbol · Atomic number · Boiling point · Melting point · Density · Atomic mass
Groups 1 · 2 · 3 · 4 · 5 · 6 · 7 · 8 · 9 · 10 · 11 · 12 · 13 · 14 · 15 · 16 · 17 · 18
Periods: 1 · 2 · 3 · 4 · 5 · 6 · 7 · 8
Series Alkalis · Alkaline earths · Lanthanides · Actinides · Transition metals · Poor metals · Metalloids · Nonmetals · Halogens · Noble gases
Blocks s-block · p-block · d-block · f-block · g-block
Explanation of above periodic table slice: Noble gases Atomic numbers in red are gases Solid borders indicate primordial elements (older than the Earth) Dashed borders indicate radioactive natural elements Dotted borders indicate radioactive synthetic elements No borders indicate undiscovered elements