polonium

properties
[ Xe ] 4 f 14 5 d 10 6 s 2 6 p 4 84 Po Periodic table
General
Name , symbol , atomic number	Polonium, Po, 84
Element category	Metals
Group , period , block	16 , 6 , p
Appearance	silvery
CAS number	7440-08-6 ( 209 Po)
EC number	231-118-2
ECHA InfoCard	100.028.289
Mass fraction of the earth's envelope	2.1 · 10 −11  ppm
Atomic
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
Physically
Physical state	firmly
Modifications	α-Po, β-Po
Crystal structure	cubic-primitive (α-Po) rhombohedral (β-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
Chemically
Oxidation states	(−2), 2, 4 , 6
Normal potential	0.37 V (Po 2+ + 2 e - → Po)
Electronegativity	2.0 ( Pauling scale )
Isotopes
isotope NH t 1/2 ZA ZE (M eV ) ZP 208 Po {syn.} 2,898 a α 5.215 204 Pb ε 1.401 208 Bi 209 Po {syn.} 103 a α 4,879 205 Pb ε 1.893 209 bi 210 Po 99.998  % 138.376 d α 5.307 206 Pb 211 Po 5 · 10 −10  % 0.516 s α 7,595 207 Pb 211 m Po {syn.} 25 s α 9,057 207 Pb IT 1.462 211 Po 212 Po 2 · 10 −12  % 304 ns α 8.78 208 Pb 212 m Po {syn.} 45.1 s α 11.8 208 Pb IT 2.922 212 Po 213 Po {syn.} 4 µs α 8.5 209 Pb 214 Po 1 · 10 −9  % 164 µs α 7.69 210 Pb 215 Po 7 10 −10  % 1.781 ms α 7.526 211 Pb β - 0.721 215 at 216 Po 1 · 10 −6  % 0.15 s α 6.78 212 Pb 217 Po {syn.} 2 s α 6.7 213 Pb 218 Po 1.6 10 −3  % 3.05 min α 6.115 214 Pb β - 0.260 218 at
For other isotopes see list of isotopes
Hazard and safety information
Radioactive
GHS hazard labeling no classification available
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 .

history

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 ).

Nowadays, however, polonium is produced in a nuclear reactor by neutron bombardment of bismuth:

${\displaystyle \mathrm {{}^{209}Bi+n\rightarrow {}^{210}Bi\rightarrow {}^{210}Po+\beta ^{-}} }$

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.

properties

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 .

The chemical properties are comparable to those of its left period - neighbor bismuth . It is metallically conductive and, with its redox nobility, stands between rhodium and silver .

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.

Isotopes

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.

Radiotoxicological significance

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.

use

In some industrial ionizers is ²¹⁰ Po used for. B. in systems in which paper, textile or synthetic materials are rolled, or when optical lenses are to be freed from static charges .

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.

The alpha emitter polonium is used in conjunction with beryllium in transportable neutron sources . The following nuclear reaction is used to generate free neutrons :

${\displaystyle \mathrm {{}_{4}^{9}Be+{}_{2}^{4}\alpha \to {}^{1}{}_{6}^{2}C+{}_{0}^{1}n} }$

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

Alexander Litvinenko

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.

Yasser Arafat

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.

links

Polonids

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 .

Oxygen compounds

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.

Sulphides

Black polonium monosulfide (PoS) is obtained by precipitating polonium dissolved in acid with hydrogen sulfide .

Hydrogen compounds

Polonium hydrogen (H ₂ Po) is a hydrogen compound that is liquid at room temperature and from which numerous polonides can be derived.

Halides

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.

Web links

Wiktionary: Polonium  - explanations of meanings, word origins, synonyms, translations

Commons : Polonium  - collection of images, videos and audio files

• Health and environmental aspects of polonium
• Method for the determination of polonium-210 in urine in a radiochemical laboratory at Forschungszentrum Jülich

Individual evidence

1. ^ Harry H. Binder: Lexicon of the chemical elements , S. Hirzel Verlag, Stuttgart 1999, ISBN 3-7776-0736-3 .
2. ↑ The values ​​for the properties (info box) are taken from www.webelements.com (Polonium) , unless otherwise stated .
3. ↑ 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 .
4. ↑ ^{a b c d e f} Entry on polonium in Kramida, A., Ralchenko, Yu., Reader, J. and NIST ASD Team (2019): NIST Atomic Spectra Database (ver. 5.7.1) . Ed .: NIST , Gaithersburg, MD. doi : 10.18434 / T4W30F ( https://physics.nist.gov/asd ). Retrieved June 13, 2020.
5. ↑ ^{a b c d e f} Entry on polonium at WebElements, https://www.webelements.com , accessed on June 13, 2020.
6. ↑ 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.
7. ^ Sieghard Neufeldt: Chronology of chemistry . John Wiley & Sons, 2012, ISBN 3-527-66284-7 , pp. 115 ( limited preview in Google Book search).
8. ^ The 14th General Meeting of the Bunsen Society. In: Polytechnisches Journal . 322, 1907, Miszelle 1, p. 364 .: "3 mg polonium salt from 5,000 kg uranium ore".
9. ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 617.
10. ↑ osti.gov: Energy Citations Database (ECD) .
11. ↑ freepatentsonline.com: Apparatus for extraction of polonium - 210 from irradiated bismuth using molten caustic .
12. ^ Royal Chemical Society: Q&A: Polonium 210 , November 27, 2006.
13. ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 620.
14. ↑ Data on polonium at KAERI (a Korean nuclear research institute)
15. ↑ Hazard warnings for Polonium 210 (PDF; 83 kB).
16. ↑ V. Zaga, C. Lygidakis u. a .: Polonium and lung cancer. In: Journal of oncology. Volume 2011, 2011, p. 860103, doi : 10.1155 / 2011/860103 , PMID 21772848 , PMC 3136189 (free full text).
17. ↑ sueddeutsche.de: Why tobacco is radioactive A smoke like 250 x-rays - per year , May 17, 2010, accessed on May 27, 2013.
18. ↑ qualm-nix.de: smoking and environmental ( Memento of 15 March 2007 at the Internet Archive )
19. ↑ MJ Tidd: The big idea: polonium, radon and cigarettes. In: Journal of the Royal Society of Medicine. Volume 101, number 3, March 2008, pp. 156-157, doi : 10.1258 / jrsm.2007.070021 , PMID 18344474 , PMC 2270238 (free full text) (review).
20. ^ Cornelius Keller, Walter Wolf, Jashovam Shani: Radionuclides, 2. Radioactive Elements and Artificial Radionuclides. In: Ullmann's Encyclopedia of Industrial Chemistry . 7th edition, Wiley-VCH, Weinheim 2012, doi : 10.1002 / 14356007.o22_o15 .
21. ↑ Petrjanow-Sokolow (ed.), Baussteine der Erde , Vol. 4, Verlag Mir Moskau, Urania Verlag Leipzig, 1977, p. 15.
22. ↑ Polonium-210 - On a Fatal Mission
23. ↑ Summary of work to date on volatile neutron source , Monsanto Chemical Company, Unit 3 abstracts of progress reports, August 16–31, 1945; Abstract ; PDF .