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neon

neon

[nee-on]
neon [Gr.,=new], gaseous chemical element; symbol Ne; at. no. 10; at. wt. 20.179; m.p. -248.67°C;; b.p. -246.048°C;; density 0.8999 grams per liter at STP; valence 0. Neon is a colorless, odorless, and tasteless gas. It is one of the inert gases in Group 18 of the periodic table; it does not form compounds in the normal chemical sense. A small amount of neon in a partially evacuated glass tube emits a bright reddish-orange glow while conducting electricity. Neon is a rare gas present in the atmosphere to a very limited extent. It is obtained as a byproduct in the production of liquid air. The greatest commercial use of neon is in advertising signs (see lighting). It is also used in high-intensity beacons, in some electron tubes, in Geiger counters, in automotive ignition timing lights, and in high-voltage warning indicators. It is used for particle detection in high-energy physics research. Neon finds use in lasers both as a light-emitting agent and as a coolant. Liquid neon is a particularly good cryogenic refrigerant since it will absorb more heat without vaporizing than an equal volume of liquid helium or liquid hydrogen. Neon was discovered in 1898 by William Ramsay and M. W. Travers.

Chemical element, chemical symbol Ne, atomic number 10. One of the noble gases, neon is colourless, odourless, tasteless, and completely unreactive. It occurs in minute amounts in the atmosphere and is obtained by fractional distillation of liquefied air. When under low pressure, it glows a bright orange-red if an electric current is passed through it. It was discovered in 1898, and since the 1920s its chief use has been in luminous tubes and bulbs.

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Neon is the chemical element that has the symbol Ne and atomic number 10. Although a very common element in the universe, it is rare on Earth. A colorless, inert noble gas under standard conditions, neon gives a distinct reddish glow when used in vacuum discharge tubes and neon lamps. It is commercially extracted from air, in which it is found in trace amounts.

History

Neon (Greek νέον(neon) meaning "new one") was discovered in 1898 by Scottish chemist William Ramsay (1852 - 1916) and English chemist Morris W. Travers (1872-1961) in London, England. Neon was discovered when Ramsay chilled a sample of the atmosphere until it became a liquid, then warmed the liquid and captured the gases as they boiled off. The three gases were krypton, xenon, and neon. On December 1910, French engineer Georges Claude made a lamp from an electrified tube of neon gas. On January 19, 1915, Claude began selling his tubes to U.S. companies; the Packard car dealership in Los Angeles was one of the first to buy it.

Isotopes

Neon has three stable isotopes: 20Ne (90.48%), 21Ne (0.27%) and 22Ne (9.25%). 21Ne and 22Ne are nucleogenic and their variations are well understood. In contrast, 20Ne is not known to be nucleogenic and the causes of its variation in the Earth have been hotly debated. The principal nuclear reactions which generate neon isotopes are neutron emission, alpha decay reactions on 24Mg and 25Mg, which produce 21Ne and 22Ne, respectively. The alpha particles are derived from uranium-series decay chains, while the neutrons are mostly produced by secondary reactions from alpha particles. The net result yields a trend towards lower 20Ne/22Ne and higher 21Ne/22Ne ratios observed in uranium-rich rocks such as granites. Isotopic analysis of exposed terrestrial rocks has demonstrated the cosmogenic production of 21Ne. This isotope is generated by spallation reactions on magnesium, sodium, silicon, and aluminium. By analyzing all three isotopes, the cosmogenic component can be resolved from magmatic neon and nucleogenic neon. This suggests that neon will be a useful tool in determining cosmic exposure ages of surficial rocks and meteorites.

Similar to xenon, neon content observed in samples of volcanic gases are enriched in 20Ne, as well as nucleogenic 21Ne, relative to 22Ne content. The neon isotopic content of these mantle-derived samples represent a non-atmospheric source of neon. The 20Ne-enriched components are attributed to exotic primordial rare gas components in the Earth, possibly representing solar neon. Elevated 20Ne abundances are found in diamonds, further suggesting a solar neon reservoir in the Earth.

Notable characteristics

Neon is the second-lightest noble gas, glows reddish-orange in a vacuum discharge tube. According to recent studies, neon is the least reactive noble gas and thus the least reactive of all elements. It has over 40 times the refrigerating capacity of liquid helium and three times that of liquid hydrogen (on a per unit volume basis). In most applications it is a less expensive refrigerant than helium.

Neon plasma has the most intense light discharge at normal voltages and currents of all the noble gases. The average color of this light to the human eye is red-orange due to many lines in this range; it also contains a strong green line which is hidden, unless the visual components are dispersed by a spectroscope.

Two quite different kinds of neon lights are in common use. Glow-discharge lamps are typically tiny, and often designed to operate at 120 volts; they are widely used as power-on indicators and in circuit-testing equipment. Neon signs and other arc-discharge devices operate instead at high voltages, often 3–15 kilovolts (3,000–15,000 volts); they can be made into (often bent) tubes a few meters long.

Occurrence

Neon is actually abundant on a universal scale: the fifth most abundant chemical element in the universe by mass, after hydrogen, helium, oxygen, and carbon (see chemical element). Its relative rarity on Earth, like that of helium, is due to its relative lightness and chemical inertness, both properties keeping it from being trapped in the condensing gas and dust clouds of the formation of smaller and warmer solid planets like Earth. Mass abundance in the universe is about 1 part in 750 and in the Sun and presumably in the proto-solar system nebula, about 1 part in 600. The Galileo spacecraft atmospheric entry probe found that even in the upper atmosphere of Jupiter, neon is reduced by about a factor of 10, to 1 part in 6,000 by mass. This may indicate that even the ice-planetesmals which brought neon into Jupiter from the outer solar system, formed in a region which was too warm for them to have kept their neon (abundances of heavier inert gases on Jupiter are several times that found in the Sun).

Neon is a monatomic gas at standard conditions. Neon is rare on Earth, found in the Earth's atmosphere at 1 part in 65,000 (by volume) or 1 part in 83,000 by mass. It is industrially produced by cryogenic fractional distillation of liquefied air.

Applications

The reddish-orange color that neon emits in neon lights is widely used to make advertising signs and is used in long tubular strips in car modification. The word "neon" is used generically for these types of lights even though many other gases and phosphors are used to produce different colors of light.

Neon is used in vacuum tubes, high-voltage indicators, lightning arrestors, wave meter tubes, television tubes, and helium-neon lasers. Liquefied neon is commercially used as a cryogenic refrigerant in applications not requiring the lower temperature range attainable with more expensive liquid helium refrigeration.

Liquid neon is actually quite expensive, and nearly impossible to obtain in small quantities for laboratory tests. For small quantities, liquid neon can be >50x more expensive than liquid helium. The driver for expense is actually rarity of the gas, not the liquefaction process.

Neon's triple point temperature of 24.5561 K is a defining fixed point in the International Temperature Scale of 1990.

Compounds

Neon is the first p-block noble gas. Theoretically neon is the least reactive of all noble gases (including helium which produces a metastable compound HHeF), and therefore generally considered to be inert. The calculated bond energies of neon with noble metals, hydrogen, berylium and boron are lesser than that of helium or any other noble gas. No true compounds including the neutral compounds of neon are known. However, the ions Ne+, (NeAr)+, (NeH)+, and (HeNe+) have been observed from optical and mass spectrometric studies, and neon is also known to form an unstable hydrate.

References

External links

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