thallium

Tl. Atomic number 81. Electron configuration [Xe]4f ¹⁴ 5d ¹⁰ 6s ² 6p ^1. Periodic table group 13 element. Discovered by W. Crookes in 1861 in the residue of a sulfuric acid synthesis plant. Named after the beautiful green emission line in its atomic spectrum, it was named after the Greek word θαλλο (thallos), meaning "green shoot". Atomic weight 204.3833(2). Two stable isotopes with mass numbers 203 (29.524(1)%) and 205 (70.48(1)%) and radioactive isotopes with mass numbers 176-212 are known.
Abundance in the earth's crust: 0.36 ppm. It is widely and thinly distributed in potassium feldspar, mica, etc., because it substitutes for K ⁺ isomorphously. However, it is a chalcophile element and occurs in association with sulfide minerals such as copper, zinc, and lead, so it is obtained as a by-product from flue dust or residue during the refining of these metals. The metal is produced by electrolysis of a saturated aqueous solution of sulfate. Rare minerals include TlAsS ₂ (lorandite) and (Cu,Tl,Ag) ₂ Se (crookesite). Two transformations are known: α (hexagonal close-packed) and β (body-centered cubic) at temperatures above 230 °C. A soft white metal similar to lead. Melting point: 304 °C, boiling point: 1457 °C. Density: 11.85 g cm ^-3 (20 °C). The metal is soluble in sulfuric acid and nitric acid, but insoluble in hydrochloric acid. Oxidation states: 1, 3. First ionization energy: 6.108 eV. Tl ^I resembles alkali metals and silver, its hydroxide TlOH is a fairly strong base, its halides are photosensitive, and all but the fluorides are poorly soluble in water. It is easily oxidized in air to produce black Tl ₂ O, which becomes yellow TlOH when it comes into contact with water. _The standard electrode potentials are Tl ⁺ /Tl-0.3363 V and Tl ^{3 +} /Tl ⁺ +1.25 V. Therefore, Tl ^III is easily reduced to Tl ^I , but a strong oxidizing agent such as Mn ^Ⅶ O ₄ ^- or Cl ₂ is required to oxidize Tl ^I to Tl ^III . The valence shell of Tl is 6s ² 6p ¹ , and the 6p electron is easily lost or can be bonded, but the 6s ² is stable and it is difficult to form Tl ^III , so thallium(I) compounds are more widely known. When Tl ^Ⅰ Cl is oxidized with Cl ₂ in an aqueous suspension or acetonitrile solution, Tl ^Ⅲ Cl ₃ is obtained. Unlike its homologue Al ^Ⅲ , Tl ^Ⅲ is a soft acid according to the HSAB principle, and so it easily forms complexes with soft bases such as ^R- (R = alkyl). R ₃ Tl ^Ⅲ (R = methyl, ethyl, isobutyl, etc.) is known. Tl ^Ⅲ Cl ₃ also easily becomes [Tl ^Ⅲ Cl ₄ ] ^- , and the complex compound is more stable.
Thallium inhibits the physiological functions of potassium, and is therefore highly toxic to the nervous system, lungs, liver, and kidneys (lethal dose: 1 g), four orders of magnitude more dangerous than cadmium. It is a Class 2 chemical substance under the PRTR (Pollutant Release and Transfer Register) Law, and is designated as Oral Class 2, Occupational Class 2, and Ecological Class 1 (class 1 is the most severe). Its traditional uses were as a rodenticide, insecticide, pigment, and wood preservative, but its use has decreased due to its toxicity to the human body. It is used as a scintillator activator for scintillation counters that measure radiation, in thallium-based III-V semiconductors for laser oscillation, phototubes, and alloys with mercury in current switches that function at low temperatures (down to -60°C), and thallium oxide in high refractive index glass (for optical fibers). A series of copper oxide high-temperature superconductors containing Tl, Ba, and Ca are known with transition temperatures of 95 to 128 K, and thin films of Ba ₂ CaCu ₂ Tl ₂ O ₈ are in practical use as microwave filters for receiving signals at mobile phone base stations. (Hg _0.8 Tl _0.2 )Ba ₂ ​​Ca ₂ Cu ₃ O _8.33 has the highest transition temperature of any stoichiometric compound, at 138 K. [CAS 7440-28-0]

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

Tl．原子番号81の元素．電子配置[Xe]4f ¹⁴5d¹⁰6s²6p¹の周期表13族元素．1861年W. Crookes(クルックス)が硫酸合成工場の残さ中に発見した．原子スペクトル中の美しい緑色の輝線にちなみ，“緑の若芽”を意味するギリシア語のθαλλο(thallos)から命名された．原子量204.3833(2)．質量数203(29.524(1)％)，205(70.48(1)％)の2種の安定同位体と，質量数176～212の放射性同位体が知られている．
地殻中の存在度0.36 ppm．K^＋ と同型置換するためカリ長石，雲母などに広く薄く分布するが，親銅元素で，銅，亜鉛，鉛などの硫化鉱物中に伴われて産出するので，これら金属の精錬の際に煙道じんまたは残さから副産物として得られる．硫酸塩飽和水溶液の電解により金属がつくられる．希少鉱物としてTlAsS₂(ローランダイト)，(Cu,Tl,Ag)₂Se(クルックス石)などがある．α(六方最密)，230 ℃ 以上でβ(体心立方)の2変態が知られる．鉛に似た軟らかい白色の金属．融点304 ℃，沸点1457 ℃．密度11.85 g cm^－3(20 ℃)．金属は硫酸，硝酸には可溶，塩酸には溶けない．酸化数1，3．第一イオン化エネルギー6.108 eV．Tl^Ⅰは，アルカリ金属および銀に似ており，水酸化物TlOHはかなり強い塩基で，ハロゲン化物は感光性があり，フッ化物以外は水に難溶である．空気中で容易に酸化されて黒色のTl₂Oを生じ，Tl₂Oは水と接触して黄色のTlOHとなる．標準電極電位 Tl^＋/Tl－0.3363 V，Tl^3＋/Tl^＋＋1.25 V．したがって Tl^Ⅲは容易に Tl^Ⅰに還元されるが，Tl^Ⅰを Tl^Ⅲに酸化するにはMn^Ⅶ O₄^－，Cl₂ のような強力な酸化剤が必要である．Tlの原子価殻は6s²6p¹で6p電子は容易に失われるか，結合にあずかれるが，6s²は安定で Tl^Ⅲにはなりにくいので，タリウム(Ⅰ)化合物のほうが多く知られる．Tl^ⅠClを水懸濁液やアセトニトリル溶液中で，Cl₂ で酸化するとTl^Ⅲ Cl₃が得られる．Tl^Ⅲは同族の Al^Ⅲなどと異なりHSAB原理による軟酸にあたるので，R^－(R ＝ アルキル)など軟塩基と錯体をつくりやすい．R₃Tl^Ⅲ(R ＝ メチル，エチル，イソブチルなど)が知られている．Tl^Ⅲ Cl₃も [Tl^ⅢCl₄]^－ となりやすく，錯化合物のほうが安定である．
タリウムはKの関与する生理作用を阻害するため，神経系，肺，肝臓，腎臓などに対する毒性が強く(致死量1 g)，カドミウムより4けたも危険とされる．PRTR(環境汚染物質排出移動登録)法・第二種化学物質として，経口クラス2，作業環境クラス2，生態クラス1の指定を受けている(1がもっとも厳しい)．従来の用途は，殺鼠剤，殺虫剤，顔料木材防腐剤などであったが，人体に対する毒性のために使用量が減った．放射線測定用シンチレーションカウンター用のシンチレーター賦活剤として，レーザー発振用タリウム系Ⅲ-Ⅴ族半導体，光電管，水銀との合金は低温(－60 ℃ まで)でもはたらく電流開閉器に，酸化タリウムは高屈折率ガラス(光ファイバー用)などとして使われる．転移温度95～128 K のTl，Ba，Caを含む一連の酸化銅系高温超伝導体が知られ，Ba₂CaCu₂Tl₂O₈薄膜は携帯電話基地局受信用マイクロ波フィルターとして実用化されている．(Hg_0.8Tl_0.2)Ba₂Ca₂Cu₃O_8.33は定比化合物最高の転移温度138 K を示す．[CAS 7440-28-0]

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