|Name, Symbol, Number||neon, Ne, 10|
|Chemical series||noble gases|
|Group, Period, Block||18, 2, p|
|Atomic mass||20.1797(6) g/mol|
|Electron configuration||1s2 2s2 2p6|
|Electrons per shell||2, 8|
|Density||(0 °C, 101.325 kPa)
|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)|
|Crystal structure||cubic face centered|
|Oxidation states||no data|
|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|
|Thermal conductivity||(300 K) 49.1 mW/(m·K)|
|Speed of sound||(gas, 0 °C) 435 m/s|
|CAS registry number||7440-01-9|
Neon (chemical symbol Ne, atomic number 10) is the fourth most abundant chemical element in the universe, but it is just a trace element in the air. As a member of the noble gas series, it is nearly inert. Under ordinary conditions, it is colorless, but in a vacuum discharge tube, it gives a reddish-orange glow. Consequently, the main use of neon is to make flashy signs for advertising. In addition, a mixture of helium and neon gases is used to make a gas laser, and liquid neon is a low-temperature refrigerant.
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. 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.
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.
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.
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+).
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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