ネオン

解説元素記号 Ne ，原子番号 10，原子量 20.1797。周期表 18族，希ガス元素の1つ。ネオンは，大気中に 0.00182%含まれ，液体空気の分留によって得られる。1898年イギリスのW・ラムゼーらが液体空気の分留の過程でクリプトンに続いて発見し、新しい気体元素の意から、ギリシア語で「新しい」を意味するネオンneonに由来して命名した。乾燥大気中には容量で約1.8ppm含まれている。希ガス元素中ではヘリウムに次いで沸点・融点が低く、空気液化後の残存気体から加圧冷却、吸着などの操作によって精製される。単体は無色，無臭の単原子気体で，沸点－245.9℃，臨界温度－228.7℃，臨界圧 28.86気圧。化学的にきわめて安定。ガイスラー管で容易に放電し，赤色の輝線スペクトルを発するので，ネオン管用に広く使われている。低圧気体での放電によって赤色の輝線スペクトルを発し、他の希ガス気体あるいは水銀蒸気などとの混合気体での放電によってさまざまな色調の発光を示す。ネオンサイン、放電管、溶接保護ガスなどに利用される。

解説Ne．原子番号10の元素．電子配置[He]2s22p6の周期表18族希ガス元素の一つ．原子量20.1797(6)．質量数20(90.48(3)％)，21(0.27(1)％)，22(9.25(3)％)の3種の安定同位体と，質量数16～32，34の放射性同位体が知られている．ネオンは，1898年にW. Ramsay(ラムゼー)とM.W. Traversにより，液体空気中に発見され，ギリシア語の“新しい”を意味するνεοζ"(neos)から命名された．大気中に65000：1の割合で微量存在し，液体空気の分留により得られる．無色，無臭の気体．融点24.48 K，沸点27.10 K．臨界定数44.49 K，2.6786 MPa，0.48192 g mL－1．液体の密度1.2070 g cm－3(沸点)．蒸発熱(沸点)1.7326 kJ mol－1．第一イオン化エネルギー21.564 eV．化学的には不活性である．普通の意味の化合物はフッ化物を含め，まだ確認されていない．理論的にも存在は疑問視されている．低圧放電により赤橙色に強く光るので，ネオンサイン用にもっとも多く用いられる．そのほか，指示灯，電子管用充填ガス，冷媒などとして用いられる．森北出版「化学辞典（第2版）

説明In 1898, Dr William Ramsay and Morris M. Travers, a Scottish scientist and a British scientist, respectively, discovered neon as a condensation product in liquefied air, as in a process similar to that used to collect neon today. Neon’s use in lighting evolved from discoveries that gases under low pressure conduct electricity. When some flowing electrons collide with residual gas in an evacuated glass tube, the resulting ions emit light as they return to their nonexcited state. The color of the light depends on the residual gas; neon gas produces a red color and argon, another inert gas often used in tubes (which are frequently and incorrectly called neon lights), produces a blue color. These two basic colors are often modified into many different hues by the addition of such elements as mercury and cadmium. The neon found on the Earth is considered to be primordial in origin. Most of the neon is sequestered in the Earth’s rocks or dissolved in water, with small amounts escaping into the atmosphere during geologic weathering. The escaped gas is slowly lost into space faster than it is replenished. Consequently, neon constitutes only a small part (0.0018%) of the Earth’s atmosphere, although this element is estimated to be the fourth most abundant in the universe.

天然物の起源Neon is the fourth most abundant element in the universe, but it makes up only 18.18ppm of the Earth’s atmosphere. It is the 82nd most abundant element on Earth. Neon is believed to be produced by radioactive decay deep in the Earth. As it rises to thesurface, it escapes into the atmosphere and is soon dissipated. Some neon is found mixed withnatural gas and several minerals. Neon is produced as a secondary product of the fractional distillation of liquid nitrogenand oxygen. Air is liquefied, and as it warms, nitrogen and oxygen boil off, leaving behindseveral other colder gases, including about 75% neon, which is then passed through activatedcharcoal to remove hydrogen and other gases.

来歴Discovered by Ramsay and Travers in 1898. Neon is a rare gaseous element present in the atmosphere to the extent of 1 part in 65,000 of air. It is obtained by liquefaction of air and separated from the other gases by fractional distillation. Natural neon is a mixture of three isotopes. Fourteen other unstable isotopes are known. It is very inert element; however, it is said to form a compound with fluorine. It is still questionable if true compounds of neon exist, but evidence is mounting in favor of their existence. The following ions are known from optical and mass spectrometric studies: Ne+, (NeAr)+, (NeH)+, and (HeNe+). Neon also forms an unstable hydrate. In a vacuum discharge tube, neon glows reddish orange. Of all the rare gases, the discharge of neon is the most intense at ordinary voltages and currents. Neon is used in making the common neon advertising signs, which accounts for its largest use. It is also used to make high-voltage indicators, lightning arrestors, wave meter tubes, and TV tubes. Neon and helium are used in making gas lasers. Liquid neon is now commercially available and is finding important application as an economical cryogenic refrigerant. It has over 40 times more refrigerating capacity per unit volume than liquid helium and more than three times that of liquid hydrogen. It is compact, inert, and is less expensive than helium when it meets refrigeration requirements. Neon costs about $800/80 cu. ft. (2265 l).

使用Gas in neon light tubes; ingredient of gaseous fillers for antifog devices, warning signals, electrical current detectors, high-voltage indicators for high-tension electric lines, lightning arresters, wave-meter tubes; in Ne-He lasers; in mixtures with He and Ar in Geiger counters. Liquid as cryogen to produce low temperetures.

一般的な説明A colorless odorless noncombustible gas. Chemically inert. The vapors are lighter than air. Nontoxic, but can act as a simple asphyxiant. Exposure of the container to prolonged heat or fire may cause NEON to rupture violently and rocket. Principal use is to fill lamp bulbs and tubes.

定義An inert colorless odorless monatomic element of the rare-gas group. Neon forms no compounds. It occurs in minute quantities (0.0018% by volume) in air and is obtained from liquid air. It is used in neon signs and lights, electrical equipment, and gas lasers. Symbol: Ne; m.p. –248.67°C; b.p. –246.05°C; d. 0.9 kg m–3 (0°C); p.n. 10; r.a.m. 20.18.