Neon
- For other uses, see Neon (disambiguation).
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General | |||||||||||||||||||||||||
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Name, Symbol, Number | neon, Ne, 10 | ||||||||||||||||||||||||
Chemical series | noble gases | ||||||||||||||||||||||||
Group, Period, Block | 18, 2, p | ||||||||||||||||||||||||
Appearance | colorless | ||||||||||||||||||||||||
Atomic mass | 20.1797(6) g/mol | ||||||||||||||||||||||||
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) | ||||||||||||||||||||||||
Critical point | 44.4 K, 2.76 MPa | ||||||||||||||||||||||||
Heat of fusion | 0.335 kJ/mol | ||||||||||||||||||||||||
Heat of vaporization | 1.71 kJ/mol | ||||||||||||||||||||||||
Heat capacity | (25 °C) 20.786 J/(mol·K) | ||||||||||||||||||||||||
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Atomic properties | |||||||||||||||||||||||||
Crystal structure | cubic face centered | ||||||||||||||||||||||||
Oxidation states | no data | ||||||||||||||||||||||||
Ionization energies (more) |
1st: 2080.7 kJ/mol | ||||||||||||||||||||||||
2nd: 3952.3 kJ/mol | |||||||||||||||||||||||||
3rd: 6122 kJ/mol | |||||||||||||||||||||||||
Atomic radius (calc.) | 38 pm | ||||||||||||||||||||||||
Covalent radius | 69 pm | ||||||||||||||||||||||||
Van der Waals radius | 154 pm | ||||||||||||||||||||||||
Miscellaneous | |||||||||||||||||||||||||
Magnetic ordering | nonmagnetic | ||||||||||||||||||||||||
Thermal conductivity | (300 K) 49.1 mW/(m·K) | ||||||||||||||||||||||||
Speed of sound | (gas, 0 °C) 435 m/s | ||||||||||||||||||||||||
CAS registry number | 7440-01-9 | ||||||||||||||||||||||||
Notable isotopes | |||||||||||||||||||||||||
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Neon (chemical symbol Ne, atomic number 10) is a chemical element that occurs in trace amounts in the air. It is a nearly inert gas and is classified as a noble gas. Under ordinary conditions, it is colorless, but in a vacuum discharge tube, it gives a reddish-orange glow.
Discovery and occurrence
Neon (from the Greek word νέος, meaning "new") was discovered by Scottish chemist William Ramsay and English chemist Morris Travers in 1898, during their studies of liquefied air.
Neon is the fourth most abundant element in the universe.[1] In the Earth's atmosphere, however, it occurs in only trace amounts—at 1 part in 65,000. It is industrially produced by cryogenic fractional distillation of liquefied air.
Notable characteristics
Neon is part of the noble gas series in the periodic table. As such, it is an extremely unreactive element. It follows helium in group 18 (former group 8A) and is placed after fluorine in period 2. The gas is composed of single atoms and is therefore described as "monatomic."
Neon is less dense than air and is the second-lightest noble gas, after helium. Its low density suggests that it may slowly leak out of the Earth's atmosphere and escape into space, thus providing an explanation for its scarcity on Earth. By contrast, argon (another noble gas) is denser than air and remains within the Earth's atmosphere.
Neon has over 40 times the refrigerating capacity of liquid helium and three times that of liquid hydrogen (on a per unit volume basis). For most applications, it is a less expensive refrigerant than helium.
Of all the rare gases, neon has the most intense discharge at normal voltages and currents. As noted above, it glows reddish-orange in a vacuum discharge tube.
Isotopes
Neon has three stable isotopes:
- 20Ne (90.48%), with 10 neutrons in the nucleus of each atom;
- 21Ne (0.27%), with 11 neutrons in the nucleus of each atom; and
- 22Ne (9.25%), with 12 neutrons in the nucleus of each atom.
21Ne and 22Ne are nucleogenic and their variations are well understood. By 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 that 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.[2]
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 also found in diamonds, further suggesting a solar neon reservoir in the Earth.[3]
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- nucleogenesis is the process that occurred a few minutes after the Big Bang when the atomic nuclei were created.
- Cosmogenic isotopes are rare radioactive isotopes created when cosmic radiation interacts with an atomic nucleus. These isotopes are produced on Earth, in Earth's atmosphere, and in extraterrestrial items such as meteorites.
- A radiogenic nuclide is one that is produced by a process of radioactive decay.
Compounds
Given the extreme inertness of neon, its compounds are hard to find. It does, however, appear to form an unstable hydrate. In addition, research involving specialized techniques (including mass spectrometry) has shown that neon can form various ions, either by itself or in combination with other elements. These ions include Ne+, (NeAr)+, (NeH)+, and (HeNe+).
Applications
The reddish-orange color that neon emits in neon lamps is widely used for advertising signs. The word "neon" has become a generic term for these types of lights, although many other gases are used to produce different colors of light.
Neon and helium may be used together to make a type of gas laser called a helium-neon laser. In addition, liquefied neon is commercially used as a cryogenic refrigerant in applications not requiring the lower temperature range attainable with liquid helium, which is more expensive.
Neon is also used in the following devices:
- vacuum tubes
- high-voltage indicators
- lightning arrestors
- wave meter tubes
- television tubes
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