neon

10 fluorine ← neon → sodium He ↑ Ne ↓ Ar Periodic table - Extended periodic table
General
Name, symbol, number	neon, Ne, 10
Element category	noble gases
Group, period, block	18, 2, p
Appearance	colorless
Standard atomic weight	20.1797(6) g·mol−1
Electron configuration	1s2 2s2 2p6
Electrons per shell	2, 8
Physical properties
Phase	gas
Density	(0 °C, 101.325 kPa) 0.9002 g/L
Melting point	24.56 K (-248.59 °C, -415.46 °F)
Boiling point	27.07 K (-246.08 °C, -410.94 °F)
Triple point	24.5561 K (-249°C), 43[1][2] kPa
Critical point	44.4 K, 2.76 MPa
Heat of fusion	0.335 kJ·mol−1
Heat of vaporization	1.71 kJ·mol−1
Specific heat capacity	(25 °C) 20.786 J·mol−1·K−1
Vapor pressure P/Pa 1 10 100 1 k 10 k 100 k at T/K 12 13 15 18 21 27
Atomic properties
Crystal structure	cubic face centered
Oxidation states	no data
Ionization energies (more)	1st: 2080.7 kJ·mol−1
	2nd: 3952.3 kJ·mol−1
	3rd: 6122 kJ·mol−1
Atomic radius (calc.)	38 pm
Covalent radius	69 pm
Van der Waals radius	154 pm
Miscellaneous
Magnetic ordering	nonmagnetic
Thermal conductivity	(300 K) 49.1x10-3 W·m−1·K−1
Speed of sound	(gas, 0 °C) 435 m/s
Bulk modulus	654 GPa
CAS registry number	7440-01-9
Selected isotopes
Main article: Isotopes of neon iso NA half-life DM DE (MeV) DP 20Ne 90.48% 20Ne is stable with 10 neutrons 21Ne 0.27% 21Ne is stable with 11 neutrons 22Ne 9.25% 22Ne is stable with 12 neutrons
References
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Neon (pronounced /ˈniːɒn/) 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-orange glow when used in discharge tubes and neon lamps.^[3][4] It is commercially extracted from air, in which it is found in trace amounts.

Contents [hide] 1 History 2 Isotopes 3 Notable characteristics 4 Occurrence 5 Applications 6 Compounds 7 See also 8 References 9 External links

[edit] History

Please help improve this section by expanding it. Further information might be found on the talk page. (December 2007)

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.^[5] 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 that boiled off were krypton, xenon, and neon.^[6] In December of 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.^[7]

[edit] Isotopes

Main article: Isotopes of neon

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^{[citation needed]} 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.^[8]

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.^[9]

[edit] Notable characteristics

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: 2.51 °C (−248.59 °C to −246.08 °C) or 4.52 °F (−415.46 °F to −410.94 °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).^[10] In most applications it is a less expensive refrigerant than helium.^[11]

Spectrum of neon with ultraviolet lines (at left) and infrared (at right) shown in white

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.^[12]

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.

[edit] 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.

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 up into the air, albeit more slowly than a helium balloon.^[13]

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).^[14]

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.^[15]

[edit] Applications

A neon sign in the shape of its name.

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 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.

The triple point temperature of Neon (24.5561 K) is a defining fixed point in the International Temperature Scale of 1990.^[1]

[edit] 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.^[16]