Noble gas
Neon is a chemical element; it has the symbol Ne and the atomic number 10. It is the second noble gas in the periodic table. Neon is a colorless, odorless, inert monatomic gas under standard conditions, with approximately two-thirds the density of air.
Neon was discovered in 1898 alongside krypton and xenon, identified as one of the three remaining rare inert elements in dry air after the removal of nitrogen, oxygen, argon, and carbon dioxide. Its discovery was marked by the distinctive bright red emission spectrum it exhibited, leading to its immediate recognition as a new element. The name neon originates from the Greek word νέον, a neuter singular form of νέος (neos), meaning 'new'. Neon is a chemically inert gas; although neon compounds do exist, they are primarily ionic molecules or fragile molecules held together by van der Waals forces.
The synthesis of most neon in the cosmos resulted from the nuclear fusion within stars of oxygen and helium through the alpha-capture process. Despite its abundant presence in the universe and Solar 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 high volatility of neon and its inability to form compounds that would anchor it to solids explain its limited presence on Earth and the inner terrestrial planets. …
Neon was discovered in 1898 by the British chemists Sir William Ramsay (1852–1916) and Morris Travers (1872–1961) in London. 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 gases nitrogen, oxygen, and argon 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 was krypton; 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 Latin novum ('new') 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."
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 it metargon. However, the subsequent spectroscopic analysis revealed it to be argon contaminated with carbon monoxide. Finally, the same team discovered xenon by the same process, in September 1898. …
Neon is the second-lightest noble gas, after helium. Like other noble gases, neon is colorless and odorless. It glows reddish-orange in a vacuum discharge tube. It has over 40 times the refrigerating capacity (per unit volume) of liquid helium and three times that of liquid hydrogen. In most applications it is a less expensive refrigerant than helium. Despite helium surpassing neon in terms of ionization 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. The helium hydride ion HeH⁺ has been experimentally observed, and high-pressure solids such as Na2He 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. 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.
Neon plasma has the most intense light discharge at normal voltages and currents of all the noble gases. …
Stable isotopes of neon are produced in stars. Neon's most abundant isotope 20Ne (90.48%) is created by the nuclear fusion of carbon and carbon in the carbon-burning process of stellar nucleosynthesis. This requires temperatures above 500 megakelvins, which occur in the cores of stars of more than 8 solar masses.
Neon is abundant on a universal scale; it is 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 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.
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. The Galileo 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. …
Two quite different kinds of neon lighting are in common use. Neon glow lamps are generally tiny, with most operating between 100 and 250 volts. They have been widely used as power-on indicators and in circuit-testing equipment, but light-emitting diodes (LEDs) now dominate in those applications. These simple neon devices were the forerunners of plasma displays and plasma television screens. Neon signs typically operate at much higher voltages (2–15 kilovolts), and the luminous tubes are commonly meters long. The glass tubing is often formed into shapes and letters for signage, as well as architectural and artistic applications.
In neon signs, neon produces an unmistakable bright reddish-orange light when electric current passes through it under low pressure. Although tube lights with other colors are often called "neon", they use different noble gases or varied colors of fluorescent lighting, for example, argon produces a lavender or blue hue. As of 2012, there are over one hundred colors available.
Neon is used in vacuum tubes, high-voltage indicators, lightning arresters, wavemeter tubes, television tubes, and helium–neon lasers. Gas mixtures that include high-purity neon are used in lasers for photolithography in semiconductor device fabrication.
Liquefied neon is commercially used as a cryogenic refrigerant in applications not requiring the lower temperature range attainable with the more extreme liquid helium refrigeration.
Neon has three stable isotopes: 20Ne (90.48%), 21Ne (0.27%) and 22Ne (9.25%). 21Ne and 22Ne are partly primordial and partly nucleogenic (i.e. made by nuclear reactions of other nuclides with neutrons or other particles in the environment) and their variations in natural abundance are well understood. In contrast, 20Ne (the chief primordial isotope made in stellar nucleosynthesis) is not known to be nucleogenic or radiogenic, except from the decay of oxygen-20, which is produced in very rare cases of cluster decay by thorium-228. The causes of the variation of 20Ne in the Earth have thus been hotly debated.
The principal nuclear reactions generating nucleogenic neon isotopes start from 24Mg and 25Mg, which produce 21Ne and 22Ne respectively, after neutron capture and immediate emission of an alpha particle. The neutrons that produce the reactions are mostly produced by secondary spallation reactions from alpha particles, in turn derived from uranium-series decay chains. The net result yields a trend towards lower 20Ne/22Ne and higher 21Ne/22Ne ratios observed in uranium-rich rocks such as granites.
In addition, isotopic analysis of exposed terrestrial rocks has demonstrated the cosmogenic (cosmic ray) 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. …