thulium

Tm. Atomic number 69. Electron configuration [Xe]4f ¹³ 6s ^2. Lanthanide element in group 3 of the periodic table. One of the rare earth elements of the yttrium group. Atomic weight 168.93421(2). It is a mononuclear element with only one stable nuclide, mass number 169. Radioactive isotopes with mass numbers 145 to 179 are known. It was discovered in rare earth minerals by PT Cleve of Sweden in 1879 and named after Thule, an ancient name for Scandinavia. It is found in euxenite, gadolinite, etc. Its abundance in the earth's crust is 0.32 ppm. It is the least abundant of the rare earth elements, along with lutetium. Silvery-white hexagonal crystal. Melting point 1545 °C, boiling point 1950 °C. Density 9.321 g cm ^-3 (20 °C). First ionization energy 6.18 eV. It dissolves slowly in water, and easily in hot water and acid. Oxidation number 3. Known compounds include _{Tm2O3 , TmF3} , and _TmI3 . The metal is obtained by reducing _TmF3 with Ca. It is similar to yttrium. The electron configuration of Tm3 ⁺ is ^4f12 , the crystal and aqueous solution are pale green, and it is paramagnetic. ¹⁷⁰ Tm decays mostly by β ^- radiation with a half-life of 128.6 d, but it emits γ-rays (84 keV) during decay by orbital electron capture with a branching rate of 0.13%, and portable X-ray sources utilizing this are used. Thulium-doped optical fibers are being considered for use as optical amplifiers for optical communications. [CAS 7440-30-4]

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

Tm．原子番号69の元素．電子配置[Xe]4f ¹³6s²の周期表3族ランタノイド元素．希土類元素イットリウム族の一つ．原子量168.93421(2)．安定核種は質量数169のみの単核種元素．質量数145～179の放射性同位体が知られている．1879年，スウェーデンのP.T. Cleve(クレーベ)が希土類鉱物中に発見し，スカンジナビアの古名Thuleにちなんで命名した．ユークセン石，ガドリン石などに存在する．地殻中の存在度0.32 ppm．希土類元素中，ルテチウムとともにもっとも存在度が低い．銀白色の六方晶系結晶．融点1545 ℃，沸点1950 ℃．密度9.321 g cm^－3(20 ℃)．第一イオン化エネルギー6.18 eV．水は徐々に，熱水，酸には容易に溶ける．酸化数3．Tm₂O₃，TmF₃，TmI₃などの化合物が知られる．金属はTmF₃をCaで還元すると得られる．イットリウムと似る．Tm^3＋ の電子配置は4f ¹²で，結晶，水溶液の色は淡緑色，常磁性である．¹⁷⁰Tm は半減期128.6 d でほとんど β^－ 崩壊するが，分岐率0.13％ の軌道電子捕獲で崩壊する際にγ線(84 keV)を放出するので，これを利用したポータブルX線源が用いられている．光通信用の光増幅器にツリウム・ドープ光ファイバーが考えられている．[CAS 7440-30-4]

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