|Name , symbol , atomic number||Polonium, Po, 84|
|Group , period , block||16 , 6 , p|
|CAS number||7440-08-6 ( 209 Po)|
|Mass fraction of the earth's envelope||2.1 · 10 −11 ppm|
|Atomic mass||209.98 u|
|Atomic radius (calculated)||190 (135) pm|
|Covalent radius||140 pm|
|Van der Waals radius||197 pm|
|Electron configuration||[ Xe ] 4 f 14 5 d 10 6 s 2 6 p 4|
|1. Ionization energy||8th.418 070 (4) eV ≈ 811.8 kJ / mol|
|2. Ionization energy||19th.3 (1.7) eV ≈ 1 860 kJ / mol|
|3. Ionization energy||27.3 (7) eV ≈ 2 630 kJ / mol|
|4. Ionization energy||36.0 (1.7) eV ≈ 3 470 kJ / mol|
|5. Ionization energy||57.0 (1.9) eV ≈ 5 500 kJ / mol|
|6. Ionization energy||69.1 (2.0) eV ≈ 6 670 kJ / mol|
|Crystal structure||cubic-primitive (α-Po)
|density||9.196 g / cm 3|
|Melting point||527 K (254 ° C)|
|boiling point||1235 K (962 ° C)|
|Molar volume||22.97 10 −6 m 3 mol −1|
|Heat of evaporation||approx. 100 kJ / mol|
|Heat of fusion||approx. 13 kJ mol −1|
|Electric conductivity||2.5 · 10 6 A · V −1 · m −1|
|Thermal conductivity||20 W m −1 K −1|
|Oxidation states||(−2), 2, 4 , 6|
|Normal potential||0.37 V (Po 2+ + 2 e - → Po)|
|Electronegativity||2.0 ( Pauling scale )|
|For other isotopes see list of isotopes|
|Hazard and safety information|
As far as possible and customary, SI units are used.
Unless otherwise noted, the data given apply to standard conditions .
Polonium is a radioactive chemical element with the element symbol Po and the atomic number 84. In the periodic table it is in the 6th main group or the 16th IUPAC group , so it is assigned to the chalcogens .
The existence of a very strongly radiating element in pitchblende containing uranium was first postulated in 1898 by the married couple Pierre and Marie Curie . In honor of Marie Curie's native Poland , they named it Polonium (from the Latin word "Polonia"). They did not succeed in isolating them, but only in 1902 by the chemist Willy Marckwald , who characterized this element as radiotellurium . Marie Curie was awarded the Nobel Prize in Chemistry in 1911 for the discovery and description of polonium (together with radium ) .
Extraction and manufacture
Polonium isotopes are intermediate products of the thorium series and the uranium-radium series , the latter producing the most common isotope 210 Po. Polonium can therefore be obtained from the processing of pitchblende (1000 tons of uranium pitchblende contain about 0.03 grams of polonium). It accumulates along with bismuth . It can then be separated from this element by means of fractional precipitation of the sulphides ( polonium sulphide is less soluble than bismuth sulphide ).
The half-life t ½ for the beta decay of 210 Bi is 5.01 days. The two elements are then separated by distillation ( boiling point of polonium: 962 ° C ; boiling point of bismuth: 1564 ° C). Another method is extraction with hydroxide melts at temperatures around 400 ° C. The world annual production is approx. 100 g.
Polonium is a shiny silver-white metal . The α-modification is the only metal that has a cubic-primitive crystal structure . Only the corners of a cube are filled with polonium atoms. This crystal structure is otherwise only found in the high pressure modifications of phosphorus and antimony .
Polonium dissolves in acids such as hydrochloric acid , sulfuric acid and nitric acid with the formation of the pink-red Po 2+ ion. Po 2+ ions in aqueous solutions are slowly oxidized to yellow Po 4+ ions, since the alpha radiation of the polonium forms oxidizing compounds in the water.
Of the polonium isotopes , all of which are radioactive, the isotopes 190 Po to 218 Po are known. The half-lives are quite different and range from about 3 · 10 −7 seconds for 212 Po to 103 years for the artificially produced 209 Po.
The most common, naturally occurring isotope 210 Po has a half-life of 138 days and breaks down into the lead isotope 206 Pb with the emission of alpha radiation . Because of this short half-life, the industrially used 210 Po is predominantly extracted artificially in nuclear power plants.
Polonium poses the greatest risk as a decay product of the radioactive noble gas radon . Radon in the air increases the risk of developing lung cancer. The actual cause is not radon, but the inhalation of the short-lived radon decay products which, in contrast to gaseous radon, accumulate in the respiratory tract. The polonium isotopes 210 Po, 212 Po, 214 Po, 216 Po and 218 Po, which are among the decay products , have the greatest radiological effect because they emit alpha particles .
While alpha radiation is shielded from dead cells by the top layer of skin, for example, when it is exposed to external effects, it has a highly damaging effect on people when alpha emitters enter the body. The polonium is distributed in the body tissue via the bloodstream. The destructive effect is initially noticeable as radiation sickness in cells that divide frequently (e.g. intestinal epithelia, bone marrow). Typical symptoms include hair loss and general weakness, diarrhea , anemia and bleeding from the nose, mouth, gums and rectum.
Polonium is excreted from the human body with a biological half-life of around 50 days. Residues and decay products are mostly found in the faeces and around 10% in the urine. In addition, incorporations are difficult to detect from the outside and a diagnosis is difficult, since hardly any gamma radiation is emitted.
Smokers are exposed to specific polonium exposure. Possible sources are both the phosphate fertilizers used in tobacco cultivation and the adsorption of atmospheric inputs by the tobacco plants. The contribution of tar carcinogens and radioactive exposure to the process of carcinogenesis are controversial. It is estimated that 9 to 14% of bronchial carcinomas in smokers are caused by radioactivity ingested through tobacco smoke.
Firestone spark plugs contained the radioactive heavy metal in the U.S. around 1940. It should ionize the air and thus extend the duration of the ignition spark.
210 Po develops 140 watts of heat per gram, which is why it was used in short-lived radionuclide batteries , for example for the Soviet lunar vehicles Lunochod 1 and Lunochod 2 . The heat output is sufficient to melt a polonium body. Today, only longer-lived isotopes of other elements are generally used.
Polonium was also used as a neutron source in nuclear weapons . For example, in the American atomic bombs Little Boy and Fat Man , which were dropped on Hiroshima and Nagasaki , initiators made of polonium and beryllium were used to start the chain reaction .
Polonium as a poison
In 2006 the former FSB agent and later Putin critic Alexander Litvinenko , who defected to the British secret service MI6 , died of the consequences of radiation sickness caused by 210 Po . The polonium had probably been given to him through contaminated tea.
As of July 2012, several studies were published that deal with the possible poisoning of the Palestinian President Yasser Arafat, who died in 2004, with 210 pos.
The polonides are salt-like compounds in which the polonide anion Po 2− is present and are considered the most stable compounds of polonium. Well-known polonides are sodium polonide , magnesium polonide and lead polonide .
Polonium (IV) oxide (PoO 2 ) x , like the oxide of its group neighbor tellurium ( tellurium dioxide , (TeO 2 ) x ), is an ionic compound that occurs in a yellow and a red modification. The black polonium (II) oxide (PoO) and polonium (VI) oxide (PoO 3 ) are also known.
Polonium halides are known with the empirical formulas PoX 2 , PoX 4 and PoX 6 . To be mentioned are polonium difluoride , polonium dichloride (ruby red), polonium dibromide (purple brown) and polonium tetrafluoride , light yellow polonium tetrachloride , red polonium tetrabromide and black polonium tetraiodide . The synthesis of polonium hexafluoride (PoF 6 ) was attempted in 1945, but did not lead to any clear results; the boiling point was estimated at −40 ° C.
- Health and environmental aspects of polonium
- Method for the determination of polonium-210 in urine in a radiochemical laboratory at Forschungszentrum Jülich
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- The values for the properties (info box) are taken from www.webelements.com (Polonium) , unless otherwise stated .
- Manjeera Mantina, Adam C. Chamberlin, Rosendo Valero, Christopher J. Cramer, Donald G. Truhlar: Consistent van der Waals Radii for the Whole Main Group. In: J. Phys. Chem. A. 2009, 113, pp. 5806-5812, doi : 10.1021 / jp8111556 .
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- Entry on polonium at WebElements, https://www.webelements.com , accessed on June 13, 2020.
- The hazards emanating from radioactivity do not belong to the properties to be classified according to the GHS labeling. With regard to other hazards, this element has either not yet been classified or a reliable and citable source has not yet been found.
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- Data on polonium at KAERI (a Korean nuclear research institute)
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