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Polonium

What is Polonium

Polonium (pronunciation: peh-LOW-nee-em) [3] is a rare, highly radioactive metalloid, classified as a Chalcogen [5] and represented by the chemical symbol Po [1, 2]. It has more than 25 isotopes, out of which Polonium-208, Polonium-209, and Polonium-210 are relatively long-lived [4], with the most stable one being Polonium-209 that undergoes radioactive disintegration to form 205Pb through α decay [3].

Polonium

Where is it Found

Being extremely rare to exist naturally [1], it is found in traces in uranium ores. The process of extracting polonium can be costly [1].

When produced artificially in the nuclear reactor, Bismuth-210 is first formed through the bombardment of Bismuth-209 with neutrons [1]. Then, Bismuth-210 undergoes beta decay to form polonium [1]. As of now, Russia is the only commercial producer of polonium in the world [1].

History

Origin of its Name: Its name has been derived from Poland, the country where the element was first isolated [1].

Who discovered it: The French-Polish physicist Marie Sklodowska Curie is credited for the discovery of polonium [1, 3].

Polonium Element

When and How was it discovered

Despite the minute polonium content (0.0001 grams) per ton of uranium [3], Marie and her husband Pierre Curie managed to extract a little amount of the element 84 from pitchblende or uranium oxide (U3O8) in 1898 [1]. Marie and Pierre Curie successfully separated the isotope 209Po that has a half-life of 103 years [1].

Previously, the Russian chemist Dmitri Mendeleev had estimated the existence of an element that would follow bismuth and would have an atomic mass of 212 [1]. Before the invention of nuclear reactors, polonium was only obtained from uranium ore and used in antistatic devices [1].

Element 84

Polonium Identification

Atomic number 84 [1]
CAS number 7440-08-6 [1]
Position in the periodic table Group Period Block
  16 [1] 6 [1] p [1]

Properties and Characteristics of Polonium

General Properties

Allotropes α-Po, β-Po [1]
Atomic mass 209 u
Relative atomic mass 209 [1]

Physical Properties

Color Silvery-gray [1, 5]
Melting point/freezing point 254 °C, 489 °F [1]
Boiling point 962 °C, 1764 °F [1]
Density 9.20 g cm-3 [1]
State of matter at room temperature (solid/liquid/gas) Solid [1, 5]
Hardness
– Brinell Unknown [6]
– Mohs Unknown [6]
– Vickers Unknown [6]
Electrical conductivity 2.3X106 S/m [6]
Thermal (heat) conductivity Unknown [6]
Specific heat Unknown [1]
Bulk modulus Unknown [1]
Shear modulus Unknown [1]
Young’s modulus Unknown [1]
Vapor pressure
– Temperature (K) 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
– Pressure (Pa)

Chemical Properties

Oxidation states 6, 4, 2 [1]
Isotopes Isotope Mass Abundance Half-life Mode of decay
  209Po 208.982 128 years α
  210Po 209.983 138.4 days α

Atomic Data of Polonium (Element 84)

Valence electrons 6 [6]
Quantum numbers 3P2 [6]
Electron configuration (noble gas configuration) [Xe] 4f145d106s26p4 [1]
Atomic structure
– Number of electrons 84 [5]
– Number of neutrons 125 [5]
– Number of protons 84 [5]
Radius of atom
– Atomic radius 1.97 Å [1]
– Covalent radius 1.42 Å [1]
Electronegativity (Pauling-scale) 2.0 [1]
Electron affinity 183.3 kJ mol-1 [1]
Ionization energy (kJ mol-1) 1st 2nd 3rd 4th 5th 6th 7th 8th
  811.828

Electron Configuration (Bohr Model) for Polonium

What is Polonium used for

Its highly radioactive nature has prevented the element from having any use in everyday life, limiting its commercial uses to the following:

  • Polonium, being an alpha-particle emitter, is used as a thin film on a stainless steel disc for scientific research [1]. It can be used in antistatic devices to help reduce static electricity created during processes like rolling paper, sheet metal, and wire [5].
  • Since one gram polonium (Po-210) can produce 137W of heat energy, and half gram Po-210 can reach a temperature of 500 °C, the element can be used as an energy source for spacecraft and satellites [1, 7].
  • Polonium-210 can be combined with an element of lower atomic weight (usually Beryllium) to form an alloy that can act as an emitter of neutrons. One application for this property includes making a neutron trigger for nuclear weapons [1, 7].

Polonium Poisoning

Polonium is highly toxic [1, 5]. Since it emits alpha particles, exposure to this radioactive element increases the chances of cancer [5]. If inhaled, swallowed, or absorbed through wounds and skin abrasions, it can cause damage to cell DNA and affect cell reproduction [8].

Interesting Facts

  • Polonium (alpha allotrope) is the only element in nature that has a simple cubic crystal structure [9].

Crystal Structure of Polonium

  • Po-210 was used to poison Alexander Litvinenko, an ex-Russian spy, in London in 2006 [8].
  • Since polonium was used as the source of power in “Lunokhod” rovers (vehicles that explored the moon’s surface) carried by the Luna E-1 spacecraft, the element 84 is sometimes represented by an image of the spacecraft [1].

How Much Does It Cost

Polonium-209 costs approximately $3,200 per microcurie [3].

References

  1. http://www.rsc.org/periodic-table/element/84/polonium
  2. https://www.livescience.com/39452-polonium.html
  3. https://education.jlab.org/itselemental/ele084.html
  4. https://www.ems.psu.edu/~radovic/Polonium_specs.pdf
  5. https://www.chemicool.com/elements/polonium.html
  6. http://periodictable.com/Elements/084/data.html
  7. http://large.stanford.edu/courses/2011/ph241/yu1/
  8. https://www.medicalnewstoday.com/articles/58088.php
  9. http://adsabs.harvard.edu/abs/2002APS..MARB28011R

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