Neon was discovered in 1898 alongsidekrypton andxenon, identified as one of the three remaining rare inert elements in dry air after the removal ofnitrogen,oxygen,argon, andcarbon dioxide. Its discovery was marked by the distinctive bright redemission spectrum it exhibited, leading to its immediate recognition as a new element. The nameneon originates from the Greek wordνέον, a neuter singular form ofνέος (neos), meaning 'new'. Neon is a chemicallyinert gas; althoughneon compounds do exist, they are primarily ionic molecules or fragile molecules held together byvan der Waals forces.
The synthesis of most neon in the cosmos resulted from thenuclear fusion within stars of oxygen andhelium through thealpha-capture process. Despite its abundant presence in theuniverse andSolar System—ranking fifth in cosmic abundance following hydrogen, helium, oxygen, and carbon—neon is comparatively scarce on Earth. It constitutes about 18.2 ppm of Earth's atmospheric volume and a lesser fraction in the Earth's crust. The highvolatility of neon and its inability to form compounds that would anchor it to solids explain its limited presence on Earth and theinner terrestrial planets. Neon's high volatility facilitated its escape fromplanetesimals under the early Solar System's nascent Sun's warmth.
Neon's notable applications include its use in low-voltageneon glow lamps,high-voltage discharge tubes, andneon advertising signs, where it emits a distinct reddish-orange glow.[16][17] This same red emission line is responsible for the characteristic red light ofhelium–neon lasers. Although neon has some applications in plasma tubes and as a refrigerant, its commercial uses are relatively limited. It is primarily obtained through thefractional distillation ofliquid air, making it significantly more expensive than helium due to air being its sole source.
Neon was discovered in 1898 by the British chemists SirWilliam Ramsay (1852–1916) andMorris Travers (1872–1961) inLondon.[12] Neon was discovered when Ramsay chilled a sample of air until it became a liquid, then warmed the liquid and captured the gases as they boiled off. The gasesnitrogen,oxygen, andargon had been identified, but the remaining gases were isolated in roughly their order of abundance, in a six-week period beginning at the end of May 1898. The first remaining gas to be identified waskrypton; the next, after krypton had been removed, was a gas which gave a brilliant red light under spectroscopic discharge. This gas, identified in June, was named "neon", the Greek analogue of the Latinnovum ('new')[18] suggested by Ramsay's son. The characteristic brilliant red-orange color emitted by gaseous neon when excited electrically was noted immediately. Travers later wrote: "the blaze of crimson light from the tube told its own story and was a sight to dwell upon and never forget."[19]
A second gas was also reported along with neon, having approximately the same density as argon but with a different spectrum – Ramsay and Travers named itmetargon.[20][12] However, the subsequent spectroscopic analysis revealed it to be argon contaminated withcarbon monoxide. Finally, the same team discoveredxenon by the same process, in September 1898.[20]
Neon's scarcity precluded its prompt application for lighting along the lines ofMoore tubes, which usednitrogen and which were commercialized in the early 1900s. After 1902,Georges Claude's companyAir Liquide produced industrial quantities of neon as a byproduct of his air-liquefaction business. In December 1910 Claude demonstrated modernneon lighting based on a sealed tube of neon. Claude tried briefly to sell neon tubes for indoor domestic lighting, due to their intensity, but the market failed because homeowners objected to the color. In 1912, Claude's associate began selling neon discharge tubes as eye-catchingadvertising signs and was instantly more successful. Neon tubes were introduced to the U.S. in 1923 with two large neon signs bought by a Los Angeles Packard car dealership. The glow and arresting red color made neon advertising completely different from the competition.[21] The intense color and vibrancy of neon equated with American society at the time, suggesting a "century of progress" and transforming cities into sensational new environments filled with radiating advertisements and "electro-graphic architecture".[22][23]
Neon played a role in the basic understanding of the nature of atoms in 1913, whenJ. J. Thomson, as part of his exploration into the composition ofcanal rays, channeled streams of neon ions through a magnetic and an electric field and measured the deflection of the streams with a photographic plate. 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 theatoms in the neongas were of higher mass than the rest. Though not understood at the time by Thomson, this was the first discovery ofisotopes ofstable atoms. Thomson's device was a crude version of the instrument we now term amass spectrometer.
The first evidence for isotopes of a stable element was provided in 1913 by experiments on neon plasma. In the bottom right corner ofJ. J. Thomson's photographic plate are the separate impact marks for the two isotopes neon-20 and neon-22.
Neon has threestable isotopes:20Ne (90.48%),21Ne (0.27%) and22Ne (9.25%).[14]21Ne and22Ne are partlyprimordial and partlynucleogenic (i.e. made by nuclear reactions of other nuclides with neutrons or other particles in the environment) and their variations innatural abundance are well understood. In contrast,20Ne (the chiefprimordial isotope made in stellarnucleosynthesis) is not known to be nucleogenic orradiogenic, except from the decay ofoxygen-20, which is produced in very rare cases ofcluster decay bythorium-228. The causes of the variation of20Ne in the Earth have thus been hotly debated.[24][25]
The principalnuclear reactions generating nucleogenic neonisotopes start from24Mg and25Mg, which produce21Ne and22Ne respectively, afterneutron capture and immediate emission of analpha particle. Theneutrons that produce the reactions are mostly produced by secondary spallation reactions from alpha particles, in turn derived fromuranium-seriesdecay chains. The net result yields a trend towards lower20Ne/22Ne and higher21Ne/22Ne ratios observed in uranium-rich rocks such asgranites.[25]
In addition, isotopic analysis of exposed terrestrial rocks has demonstrated thecosmogenic (cosmic ray) production of21Ne. This isotope is generated byspallation reactions onmagnesium,sodium,silicon, andaluminium. By analyzing all three isotopes, the cosmogenic component can be resolved frommagmatic neon and nucleogenic neon. This suggests that neon will be a useful tool in determining cosmic exposure ages of surface rocks andmeteorites.[26]
Neon insolar wind contains a higher proportion of20Ne than nucleogenic and cosmogenic sources.[25] Neon content observed in samples ofvolcanicgases anddiamonds is also enriched in20Ne, suggesting a primordial, possibly solar origin.[27]
Neon is the second-lightest noble gas, afterhelium. Like other noble gases, neon is colorless and odorless. It glows reddish-orange in avacuum discharge tube. It has over 40 times the refrigerating capacity (per unit volume) of liquid helium and three times that of liquidhydrogen.[3] In most applications it is a less expensiverefrigerant than helium.[28][29] Despite helium surpassing neon in terms ofionization energy, neon is theorized to be the chemically least reactive of all the elements, even less so than the former. Multiple computational studies suggest that helium can form stable chemical species under extreme conditions. Thehelium hydride ion HeH⁺ has been experimentally observed, and high-pressure solids such asNa2He have also been confirmed. Additionally, theoretical works predict that helium hydride fluoride (HHeF), a neutral compound from HeH+ could be stable under extreme pressure, whereas the analogous neon compound HNeF appears unbound and therefore nonexistent. In contrast, no stable neutral or covalent neon compounds are known to exist under any pressure or temperature.[30] While a neon-containing anion complex [B12(CN)11Ne]- has been predicted theoretically, its existence has yet to be proven experimentally, leaving neon as the only noble gas for which no compounds have been definitively confirmed to exist.[31]
Theemission spectrum of neon shows individual wavelengths of light contributing to its perceived color when heated.
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.[32]
Neon is abundant on a universal scale; it is thefifth most abundant chemical element in the universe by mass, after hydrogen, helium, oxygen, and carbon (seechemical element).[35] 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 that formed the 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.[36]
Neon's abundance in the universe is about 1 part in 750 by mass; in the Sun and presumably in its proto-solar system nebula, about 1 part in 600.[citation needed] TheGalileo spacecraft atmospheric entry probe found that 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 the ice-planetesimals that brought neon into Jupiter from the outer solar system formed in a region that was too warm to retain the neon atmospheric component (abundances of heavier inert gases on Jupiter are several times that found in the Sun),[37] or that neon is selectively sequestered in the planet's interior.[38]
Neon comprises 1 part in 55,000 in theEarth's atmosphere, or 18.2 ppm by volume (this is about the same as the molecule or mole fraction), or 1 part in 79,000 of air by mass. It comprises a smaller fraction in the crust. It is industrially produced by cryogenicfractional distillation of liquefied air.[3]
Neon is the firstp-block noble gas and the first element with a true octet of electrons. It isinert: as is the case with its lighter analog,helium, no strongly bound neutralmolecules containing neon have been identified. An example of neon compound is Cr(CO)5Ne, which contains a very weak Ne-Cr bond.[41] Theions [NeAr]+, [NeH]+, and [HeNe]+ have been observed from optical andmass spectrometric studies.[3] Solid neonclathrate hydrate was produced from water ice and neon gas at pressures 350–480 MPa and temperatures about −30 °C.[42] Ne atoms are not bonded to water and can freely move through this material. They can be extracted by placing the clathrate into a vacuum chamber for several days, yieldingice XVI, the least dense crystalline form of water.[40]
The familiarPauling electronegativity scale relies upon chemical bond energies, but such values have obviously not been measured for inert helium and neon. TheAllen electronegativity scale, which relies only upon (measurable) atomic energies, identifies neon as the most electronegative element, closely followed by fluorine and helium.[43]
Neon is produced from air incryogenicair-separation plants. A gas-phase mixture mainly of nitrogen, neon, helium, and hydrogen[45] is withdrawn from the main condenser at the top of the high-pressure air-separation column and fed to the bottom of a side column forrectification of the neon.[46] It can then be further purified from helium by bringing it into contact with activated charcoal. Hydrogen is purified from the neon by adding oxygen so water is formed and is condensed.[45] 1 pound (0.45 kg) of pure neon can be produced from the processing of 88,000 pounds (40,000 kg) of the gas-phase mixture.[45]
Two quite different kinds ofneon lighting are in common use.Neon glow lamps are generally tiny, with most operating between 100 and 250volts.[53] They have been widely used as power-on indicators and in circuit-testing equipment, butlight-emitting diodes (LEDs) now dominate in those applications. These simple neon devices were the forerunners ofplasma displays and plasma television screens.[54][55]Neon signs typically operate at much higher voltages (2–15kilovolts), and the luminous tubes are commonly meters long.[56] The glass tubing is often formed into shapes and letters for signage, as well as architectural and artistic applications.
Inneon signs, neon produces an unmistakable bright reddish-orange light whenelectric current passes through it under low pressure.[57] Although tube lights with other colors are often called "neon", they use differentnoble gases or varied colors offluorescent lighting, for example,argon produces a lavender or blue hue.[58] As of 2012, there are over one hundred colors available.[59]
Liquefied neon is commercially used as acryogenicrefrigerant in applications not requiring the lower temperature range attainable with the more extremeliquid helium refrigeration.
^Shuen-Chen Hwang, Robert D. Lein, Daniel A. Morgan (2005). "Noble Gases". inKirk Othmer Encyclopedia of Chemical Technology, pages 343–383. Wiley.doi:10.1002/0471238961.0701190508230114.a01.pub2
^Ne(0) has been observed in Cr(CO)5Ne; seePerutz, Robin N.; Turner, James J. (August 1975). "Photochemistry of the Group 6 hexacarbonyls in low-temperature matrices. III. Interaction of the pentacarbonyls with noble gases and other matrices".Journal of the American Chemical Society.97 (17):4791–4800.Bibcode:1975JAChS..97.4791P.doi:10.1021/ja00850a001.
^Arblaster, John W. (2018).Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International.ISBN978-1-62708-155-9.
^Group 18 refers to the modern numbering of the periodic table. Older numberings described the rare gases as Group 0 or Group VIIIA (sometimes shortened to 8). See alsoGroup (periodic table).
^Mangum, Aja (8 December 2007)."Neon: A Brief History".New York Magazine.Archived from the original on 15 April 2008. Retrieved20 May 2008.
^Golec, Michael J. (2010). "Logo/Local Intensities: Lacan, the Discourse of the Other, and the Solicitation to "Enjoy"".Design and Culture.2 (2):167–181.doi:10.2752/175470710X12696138525622.S2CID144257608.
^Wolfe, Tom (October 1968). "Electro-Graphic Architecture".Architecture Canada.
^Dickin, Alan P (2005). "Neon".Radiogenic isotope geology. Cambridge University Press. p. 303.ISBN978-0-521-82316-6.
^Perutz, Robin N.; Turner, James J. (August 1975). "Photochemistry of the Group 6 hexacarbonyls in low-temperature matrices. III. Interaction of the pentacarbonyls with noble gases and other matrices".Journal of the American Chemical Society.97 (17):4791–4800.Bibcode:1975JAChS..97.4791P.doi:10.1021/ja00850a001.
^Allen, Leland C. (1989). "Electronegativity is the average one-electron energy of the valence-shell electrons in ground-state free atoms".Journal of the American Chemical Society.111 (25):9003–9014.Bibcode:1989JAChS.111.9003A.doi:10.1021/ja00207a003.
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