selenium

Se. Atomic number 34. Electron configuration [Ar] ^{3d104s24p4 .} Nonmetallic element in group ¹⁶ of the periodic table. Atomic weight 78.96(3). Six stable isotopes are known: mass numbers 74 (0.89(4)%), 76 (9.372(9)%), 77 (7.63(16)%), 78 (23.77(28)%), 80 (49.61(41)%), and 82 (8.73(22)%). Radioactive isotopes with mass numbers between 64 and 94 are also known. Se was first isolated from lead mud by J. J. Berzelius of Sweden in 1817. In correspondence with the fact that tellurium was named after the Latin word tellus, which meant the "earth goddess" in Roman mythology, selenium was named after the "moon goddess" in Greek mythology, Σεληνη (Selènè) selene. In his "Semitsu Kaisyu" published in 1837, Udagawa Yoan wrote that it was selenium.
Selenium is widely distributed on Earth, but in much smaller quantities than sulfur. Small amounts are produced in free form, but it is mainly found in sulfide ores of copper, silver, lead, and iron. Its abundance in the Earth's crust is 0.05 ppm. It is obtained as a by-product of precious metal recovery from the anode slime produced in copper electrorefining. Japan is the world's leading producer of selenium, produced by copper refining companies. Selenium exists in various allotropes, and forms many inorganic and organic compounds similar to sulfur compounds. When selenium is heated above its melting point and cooled, it becomes a red glass-like mass, which is a mixture of allotropes. When this red glass-like selenium is dissolved in carbon disulfide or benzene and slowly evaporated below 72 °C, red monoclinic α-phase selenium is produced, and when it is rapidly evaporated above 72 °C, red monoclinic β-phase selenium is produced. Both contain zigzag rings of Se _8. Se-Se0.234 nm. ∠105.7°. Density 4.4 g cm ^-3 . When red selenium glass is heated above 150 °C, it transforms into hexagonal gray selenium, which is the most thermodynamically stable and metallic. Infinite spiral structure. Se-Se0.2373 nm. ∠103.1°. Melting point 217 °C, boiling point 684.9 °C. Density 4.79 g cm ^-3 . It is photoconductive. The red amorphous allotrope is produced by reducing an aqueous solution of selenite with SO ₂ or by quenching selenium vapor. Density 4.26 g cm ^-3 . It is not electrically conductive like gray selenium. When molten selenium is quenched, black selenium glass is obtained. Density 4.285 g cm ^-3 . It is brittle and translucent, and contains macrocyclic structures. It transforms into gray selenium gradually at room temperature and rapidly at high temperatures. First ionization energy 9.752 eV. It forms compounds with positive elements with an oxidation number of -2 (e.g., H ₂ Se) and with negative elements with oxidation numbers of 2, 4, and 6 (e.g., SeCl ₂ , SeO ₂ , SeO ₃ ). It usually has oxidation numbers of 4 and 6. Gray selenium is slowly oxidized with H ₂ O at 160 °C. It reacts directly with _{F 2} , Cl ₂ , Br ₂ , and S. It is insoluble in dilute hydrochloric acid and dilute sulfuric acid, but soluble in oxidizing concentrated nitric acid and concentrated sulfuric acid.
It is often added to glass to counter the green color caused by iron and to block heat rays. It is also used as a raw material for blue and red pigments, as a rubber additive, and as a colorant for glass and ceramics. Its electrical conductivity changes depending on the intensity of light, so it is also used in photocells and phototubes. Newer uses include digital X-ray detection devices that use amorphous selenium. Its use as a photoconductor in dry copy machines has almost disappeared. "Selenium and selenium compounds" are designated as Class 1 substances under the PRTR Law. Oral Class 2 (water quality standard value 0.01 mg L ^-1 or less). Designated as a poisonous substance under the Poisonous and Deleterious Substances Control Law. Water Pollution Prevention Law, effluent standard value 0.1 mg L ^-1 or less. Soil Contamination Countermeasures Law, specified Class 2 harmful substance, soil content 150 mg/kg or less. Air Pollution Control Law, harmful air pollutant. [CAS 7782-49-2]

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

Se．原子番号34の元素．電子配置[Ar]3d¹⁰4s²4p⁴の周期表16族非金属元素．原子量78.96(3)．質量数74(0.89(4)％)，76(9.372(9)％)，77(7.63(16)％)，78(23.77(28)％)，80(49.61(41)％)，82(8.73(22)％)の6種の安定同位体と，質量数64～94の放射性同位体が知られている．1817年スウェーデンのJ.J. Berzelius(ベルセリウス)により鉛室泥中からはじめて分離された．テルルがローマ神話の“地球の女神”を意味するラテン語tellusにちなんで命名されたことに対応して，ギリシア神話の“月の女神”Σεληνη(Selènè)seleneからseleniumと命名した．宇田川榕菴は天保8年(1837年)に出版した「舎密開宗」で，攝列紐母(セレニウム)としている．
地球上に広く分布しているが，その量は硫黄よりずっと少ない．少量は遊離の形で産出するが，おもに銅，銀，鉛，鉄の硫化鉱中に含まれて産出する．地殻中の存在度0.05 ppm．銅電解精錬でできる陽極スライムから，貴金属回収の際に副産物として得られる．日本のセレン生産量は世界主位で，銅精錬会社が生産している．セレンには種々の同素体が存在し，硫黄化合物に似た多くの無機・有機化合物をつくる．セレンを融点以上に加熱して冷却すると，赤色ガラス状の塊となるが，これは同素体の混合物である．この赤色ガラス状セレンを二硫化炭素かベンゼンに溶かし，72 ℃ 以下でゆっくり蒸発させると赤色の単斜晶系のα相セレンを生じ，72 ℃ 以上で急速に蒸発させると赤色の単斜晶系のβ相セレンが得られる．どちらもジグザグ環状 Se₈ を含む．Se-Se0.234 nm．∠105.7°．密度4.4 g cm^－3．赤色ガラス状セレンを150 ℃ 以上に加熱すると，熱力学的にもっとも安定で金属性を示す六方晶系の灰色セレンに変化する．らせん無限構造．Se-Se0.2373 nm．∠103.1°．融点217 ℃，沸点684.9 ℃．密度4.79 g cm^－3．光伝導性がある．亜セレン酸水溶液をSO₂で還元するか，セレン蒸気を急冷すると赤色の無定形同素体ができる．密度4.26 g cm^－3．灰色セレンのような導電性がない．セレン融液を急冷すると黒色ガラス状セレンが得られる．密度4.285 g cm^－3．もろく半透明，大環状構造を含む．室温で徐々に，高温で急速に灰色セレンにかわる．第一イオン化エネルギー9.752 eV．陽性の元素とは－2の酸化数で化合物(例：H₂Se)を，陰性の元素とは2，4，6の酸化数で化合物(例：SeCl₂，SeO₂，SeO₃)をつくる．普通，4および6の酸化数をとる．灰色セレンはH₂Oと160 ℃ で徐々に酸化される．F₂，Cl₂，Br₂，Sと直接反応する．希塩酸，希硫酸に不溶，酸化性の濃硝酸，濃硫酸に可溶．
ガラスに，鉄分による緑色を打ち消すためと熱線遮断の目的で添加される量が多い．そのほか，青色顔料，赤色顔料の原料，ゴム添加剤，ガラス・陶磁器の着色剤として使用されている．光の強度に応じて導電率が変化するため，光電池や光電管にも利用されている．新しい用途として，アモルファス・セレン利用のX線のデジタル検出装置などがある．乾式コピー機の感光体としての用途はほぼ消滅した．「セレン及びセレン化合物」は，PRTR法・第一種指定物質．経口クラス2(水質基準値0.01 mg L^－1 以下)．毒物劇物取締法毒物指定．水質汚濁防止法排水基準値0.1 mg L^－1 以下．土壌汚染対策法特定第二種有害物質で土壌含有量150 mg/kg 以下．大気汚染防止法 有害大気汚染物質．[CAS 7782-49-2]

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