지구에서 가장 희귀한 원소는 뭘까요? (할 수있다 2024)
아스타틴 (At), 방사성 화학 원소 및 할로겐 원소의 가장 무거운 구성원, 또는 주기율표의 17 족 (VIIa). 안정한 동위 원소가없는 아스타틴은 미국 물리학 자 Dale R. Corson, Kenneth R. MacKenzie 및 Emilio Segrè에 의해 캘리포니아 대학에서 합성 적으로 처음 생산되었습니다 (1940 년). 아스타틴 -211 및 중성자. 자연적으로 발생하는 아스타틴 동위 원소는 세 가지 자연 방사성 붕괴 시리즈에서 미세한 양으로 발견되었으며, 이는 작은 분지 (우라늄 시리즈의 아스타틴 -218, 토륨 시리즈의 아스타틴 -216, 아스타틴 -215 및 아스타틴- 악티늄 시리즈의 219). 32 개의 동위 원소가 알려져있다. 반감기가 8.1 시간 인 아스타틴 -210이 가장 오래 산다.아스타틴은 안정되거나 수명이 긴 동위 원소가 없기 때문에 그리스어 단어 astatos에서“불안정한”이라는 이름을 붙였습니다.
할로겐
(Br), 요오드 (I), 아스타틴 (At) 및 테 네신 (Ts). 그들은 그리스어 뿌리 hal- (“소금”)에서 할로겐이라는 이름을 받았습니다.
요소 속성
| 원자 번호 | 85 |
|---|---|
| 가장 안정적인 동위 원소 | 210 |
| 산화 상태 | −1, +1, +3 (?), +5, +7 (?) |
| 전자 구성. | (Xe) 4f 14 5d 10 6s 2 6p 5 |
생산 및 사용
아스타틴을 얻는 유일한 실제 방법은 핵 반응을 통해 그것을 합성하는 것입니다. 아스타틴은 일반적으로 일반 방정식에 따라 준비됩니다.
which indicates that bismuth-209 takes up one alpha particle and emits x neutrons to form an isotope of astatine, whose atomic weight depends on the number of neutrons lost. Metallic bismuth may be used as a target material. From this, astatine may readily be removed by distillation in air from a stainless-steel tube. The free element begins to distill at 271 °C (520 °F, or the melting point of bismuth), but the operation is best carried out at 800 °C (1,500 °F) with subsequent redistillation. If an aqueous solution of astatine is desired, the element may be separated by washing with an appropriate aqueous solution. Alternatively, the halogen may be removed from the target by chemical methods, such as dissolving in nitric acid, with the latter being removed by boiling.
Another procedure involves the use of a metallic thorium target, which—after bombardment—is dissolved in concentrated hydrochloric acid containing hydrogen fluoride and chlorine.
Analysis
Because of the short half-lives of astatine isotopes, only very small quantities have been available for study. With the exception of a few spectrometric and mass-spectrometric studies, most investigations of astatine chemistry have used tracer techniques, which involve using chemical reactions in a solution with similarly reacting elements as carriers. The amount of astatine is then calculated from the measured radioactivity of the reaction products. However, the rarity of astatine means that these solutions are extremely dilute, with concentrations around or below 10−10 molarity (the number of moles per litre of solution). At such concentrations, the effects of impurities can be very serious, especially for a halogen such as astatine, which exists in several oxidation states and can form many organic compounds. Iodine has been used as a carrier in most experiments. Techniques applied include coprecipitation, solvent extraction, ion exchange, and other forms of chromatography (separation by adsorption differences), electrodeposition (deposition by an electric current), electromigration (movement in an electric field), and diffusion. A direct identification of some astatine compounds has been made by mass spectrometry.
Except for nuclear properties, the only physical property of astatine to be measured directly is the spectrum of atomic astatine. Other physical properties have been predicted from theory and by extrapolation from the properties of other elements.
Chemical properties
Some of the chemical properties of the element have been established. It generally resembles iodine. Thus, like iodine, it concentrates in the thyroid gland of higher animals. A substantial portion, however, is distributed throughout the body and acts as an internal radiation source.
The astatide ion, At−, is quantitatively coprecipitated with insoluble iodides, such as silver iodide or thallium iodide. The diffusion coefficient of the iodide ion is 1.42 times that of the astatide ion, which moves more slowly toward the anode than the former under given conditions. The ion is formed by reduction of the element, using zinc or sulfur dioxide. It is oxidized to the zero valence state by the ferric ion, Fe3+, iodine (I2), and dilute nitric acid. Thus, the astatide ion is a stronger reducing agent than the iodide ion, and free iodine is a stronger oxidizing agent than astatine.
Free astatine is characterized by volatility from solution and by extractability into organic solvents. It undergoes disproportionation in alkaline media. Astatine is coprecipitated with cesium iodide and thus appears to form polyhalide anions. Astatine extracted into chloroform has been shown to coprecipitate homogeneously with iodine when a portion of the latter is crystallized. Astatine seems to be present as the iodide, which appears to be more polar (i.e., showing separation of electric charge) in character than iodine bromide. It is somewhat soluble in water and much more soluble in benzene and carbon tetrachloride.
Astatine is known to occur in positive oxidation numbers. The astatate ion, (AtO3)−, is coprecipitated with insoluble iodates, such as silver iodate (AgIO3), and is obtained by the oxidation of lower oxidation states with hypochlorite, periodate, or persulfate. So far no evidence for perastatate has been found, but this may be because the ion, (AtO6)5−, may show little tendency to coprecipitate with potassium iodate (KIO4).
Astatine in the +1 state is stabilized by complexation, and complexes formulated as dipyridine astatine perchlorate [At(py)2] [ClO4] and dipyridine astatine nitrate [At(py)2] [NO3] have been prepared. Compounds with the formulas (C6H5)AtCl2, (C6H5)2AtCl, and (C6H5)AtO2 have also been obtained. A variety of methods may be used to synthesize astatobenzene, C6H5At.
