argon

Ar. An element with atomic number 18. It is a rare gas element in group 18 of the periodic table with the electron configuration [Ne]3s ² 3p ^6. Its atomic weight is 39.948(1). It is close to being a mononuclear species, with ⁴⁰ Ar99.6003(1)%, ³⁸ Ar0.0632%, and ³⁶ Ar0.3365%. Radioactive nuclides with mass numbers between 30 and 53 are known. It was discovered in 1894 by W. Ramsay and J. Rayleigh, and was named after the Greek word αργοσ, which means lazy person, because it is inactive. It accounts for 9340 ppm by volume of the atmosphere. The atmosphere of Mars also contains 1.6% Ar. It can be obtained as an element by fractional distillation of liquid air. It can be purified by repeated fractional distillation, heating with alkali metals (removing nitrogen and oxygen), fractional adsorption with activated charcoal, fractional evaporation, and gas chromatography. It is a colorless, odorless gas. Melting point 83.8 K (-189.3 °C), boiling point 87.28 K (-185.87 °C). Critical point 150.86 K (-122.3 °C). 4.898 MPa (48.35 atm). 13.41 mol L ^-1 (0.5356 g mL ^-1 ). Triple point 87.78 K. Liquid density 34.93 mol L ^-1 (1.393 g mL ^-1 ) (boiling point). Heat of vaporization 6.516 kJ mol ^-1 (boiling point). First ionization energy 1520.4 kJ mol ^-1 (15.760 eV). It is chemically inert. It forms inclusion compounds with hydroquinone and [C ₆ H ₄ (OH) ₂ ] ₃ ･0.67Ar, and with water and 6H ₂ O･Ar. It is used as an inert atmosphere in arc welding, in the manufacture of titanium, silicon for semiconductors, and germanium crystals, and as a fill gas for incandescent and fluorescent lamps. The liquid is used as a detector medium for high-energy physics. [CAS 7440-37-1]

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

Ar．原子番号18の元素．電子配置[Ne]3s²3p⁶の周期表18族希ガス元素．原子量39.948(1)．⁴⁰Ar99.6003(1)％，³⁸Ar0.0632％，³⁶Ar0.3365％ からなり単核種に近い．質量数30～53までの放射性核種が知られている．1894年，W. Ramsay(ラムゼー)とJ. Rayleighによって発見され，不活性なところから怠け者を意味するギリシア語αργοσをとって命名された．大気の9340体積 ppm を占める．火星の大気中にも1.6％Arが含まれる．液体空気の分留によって単体が得られる．精製は，分留の反復，アルカリ金属との加熱(窒素，酸素の除去)，活性炭による分別吸着，分別蒸発，ガスクロマトグラフィーによって精製される．無色，無臭の気体．融点83.8 K(－189.3 ℃)，沸点87.28 K(－185.87 ℃)．臨界点150.86 K(－122.3 ℃)．4.898 MPa(48.35 atm)．13.41 mol L^－1(0.5356 g mL^－1)．三重点87.78 K．液体の密度34.93 mol L^－1(1.393 g mL^－1)(沸点)．蒸発熱6.516 kJ mol^－1(沸点)．第一イオン化エネルギー1520.4 kJ mol^－1(15.760 eV)．化学的には不活性である．ヒドロキノンと[C₆H₄(OH)₂]₃･0.67Ar，水と6H₂O･Arの包接化合物をつくる．アーク溶接，チタン，半導体用ケイ素，ゲルマニウム結晶製造の際の不活性雰囲気，白熱電球，蛍光灯充填ガスとして用いられる．液体は高エネルギー物理学用検出器の媒質に使われる．[CAS 7440-37-1]

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