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Neon is the chemical element that has the symbol Ne and an atomic number of 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-orange glow when used in discharge tubes and neon lamps and advertising signs. It is commercially extracted from air, in which it is found in trace amounts.
Neon (Greek νέον (neon) meaning "new one") was discovered in 1898 by the British chemists Sir William Ramsay (1852–1916) and Morris W. Travers (1872–1961) in London. 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. After nitrogen, oxygen, and argon, the three gases that boiled off were krypton, xenon, and neon.
In December 1910, French engineer Georges Claude made a lamp from an electrified tube of neon gas. In 1912, Claude's associate began selling neon discharge tubes as advertising signs. They were introduced to U.S. in 1923, when two large neon signs were bought by a Los Angeles Packard car dealership. The glow and arresting red color made neon advertising completely different from the competition.
Neon played a role in the basic understanding of the nature of atoms in 1913, when J. J. Thomson, as part of his exploration into the composition of canal rays, channeled streams of neon ions through a magnetic and an electric field and measured their deflection by placing a photographic plate in their path. Thomson observed two separate patches of light on the photographic plate (see image), which suggested two different parabolas of deflection. Thomson eventually concluded that some of the atoms in the neon gas were of higher mass than the rest. Though not understood at the time by Thompson, this was the first discovery of isotopes of stable atoms. It was made using a crude version of an instrument we now term a mass spectrometer.
Neon is a noble gas, and the second lightest inert gas. 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 (the cosmogenic primordial isotope made in stellar nucleosynthesis) is not known to be nucleogenic, save for cluster decay production, which is thought to produce only a small amount. The causes of the variation of 20Ne in the Earth have thus 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 represents 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.
Neon is the second-lightest noble gas. It 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. Also, neon has the narrowest liquid range of any element: from 24.55 K to 27.05 K (−248.45 °C to −245.95 °C, or −415.21 °F to −410.71 °F). 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; they can be made into (often bent) tubes a few meters long.
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, high vapor pressure at very low temperatures, and chemical inertness, all properties which tend to keep it from being trapped in the condensing gas and dust clouds which resulted in the formation of smaller and warmer solid planets like Earth.
Neon is monatomic, making it lighter than the molecules of diatomic nitrogen and oxygen which form the bulk of Earth's atmosphere; a balloon filled with neon will rise in air, albeit more slowly than a helium balloon.
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, the abundance of neon is reduced (depleted) by about a factor of 10, to a level of 1 part in 6,000 by mass. This may indicate that even the ice-planetesimals 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.
Neon is often used in signs and produces an unmistakable bright reddish-orange light. Although still referred to as "neon", all other colors are generated with the other noble gases or by many colors of fluorescent lighting.
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 extreme liquid helium refrigeration.
Liquid neon is expensive – for small quantities, its price can be more than 55 times that of liquid helium. The driver for expense is rarity of neon, not the liquefaction process.
The triple point temperature of neon (24.5561 K) is a defining fixed point in the International Temperature Scale of 1990.
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, beryllium 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 there are some unverified reports of an unstable hydrate.
* Expansion ratio
1. ^ a b Preston-Thomas, H. (1990). "The International Temperature Scale of 1990 (ITS-90)". Metrologia 27: 3-10. http://www.bipm.org/en/publications/its-90.html.
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