Polonium (Po)

Polonium is a chemical element with the atomic number 84 in the periodic table. It’s a rare and highly radioactive metal. The natural abundance of element 84 in Earth’s crust is only 2 × 10 −10 milligrams per kilogram. 

Being a member of the chalcogen family of the periodic table, this radioactive metalloid has six valence electrons and six orbitals. Polonium is the most radioactive chemical element in the world with the largest number of isotopes among the chemical elements. Polonium-210 isotope is an exceptionally strong emitter of alpha particles that may lead to bone marrow damage and self-destruction of the cells in our body.

Chemical and Physical Properties of Polonium

Atomic number84
Period6 (p-block)
ColorA silvery-gray metal
Physical stateSolid at 20°C
Half-lifeFrom 0.5 milliseconds to 125.2 years
Density9.4 g/cm³
Melting point254°C, 489°F, 527 K
Boiling point962°C, 1764°F, 1235 K
Van der Waals radius0.164 nm
Ionic radius
Atomic radius1.53 Å
Covalent radius1.46 Å
Atomic weight[209] g.mol-1
Atomic volume22.23 cm³/mol
Most characteristic isotope209Po
Electronic shell[Xe] 4f14 5d10 6s2 6p4
Oxydation states(4),2
Discovery date1898
DiscoverersPierre and Marie Curie
Location of discoveryFrance
Name originNamed for Poland, native country of Marie Curie.
UsesUsed in industrial equipment to eliminate static electricity
DescriptionUnstable, radioactive member of the halogen group.

With the periodic table symbol Po, atomic number 84, atomic mass of [209] g.mol-1, and electron configuration [Xe] 4f145d106s26p4, polonium is a highly radioactive and reactive silvery-gray semi-metal. It reaches its boiling point at 962°C, 1764°F, 1235 K, while the melting point is achieved at 254°C, 489°F, 527 K. This member of the chalcogen family of elements has an electronegativity of 2.0 according to Pauling, whereas the atomic radius according to van der Waals is 0.164 nm. 

Polonium resembles the chemical properties of the elements bismuth, selenium, and tellurium. Since its electrical conductivity decreases as its temperature rises, polonium is also classified as a metal substance in the periodic table. In fact, the position of element 84 according to Mendeleev’s classification of elements could make polonium a metal, a metalloid, or a nonmetal.

How Was Polonium Discovered?

The success story of the two distinguished chemists Pierre and Marie Currie did not begin with the discovery of radium. In 1898, they began a series of detailed analyses of mineral ores in an attempt to detect radioactivity in some of them. A naturally occurring ore called pitchblende was the first mineral sample in which Pierre and Marie Currie attempted to detect a source of radioactivity which ultimately led these two great scientists to the discovery of polonium.

After Marie Sklodowska Curie ambitiously analyzed all known elements of the periodic table, she realized that only two of them give off radiation – uranium and thorium. As a next step, she decided to analyze the mineral ores containing these two elements. Observing a pitchblende sample obtained from the geological museum, Marie Curie noticed that this uranium ore is more active than uranium. In her opinion, there was clearly a new radioactive chemical element that was even more radioactive than element 92. 

Sharing her findings with her husband Pierre Curie, she invited him to join her on this new project – an idea that Pierre eagerly accepted. A more detailed analysis of the pitchblende ore informed them that the radioactivity is emitted from the fractions containing bismuth or barium

This realization called for an even more detailed look at the atomic structure of the ore Marie and Pierre studied. The continued analysis of the bismuth fractions resulted in a residue that showed even greater activity. This activity was a result of a chemical that turned out to be even 300 times more radioactive than uranium. It was element 84 – polonium. 

In 1911, Marie Sklodowska Curie became the first woman in the world of science to receive the Nobel Prize in Chemistry for the discovery of the radioactive elements polonium and radium. 

How Did Polonium Get Its Name?

Being her first chemical discovery, the Polish scientist Marie Curie named the new element polonium (Po) after her home country, Poland. 

Where Can You Find Polonium?

Polonium is an extremely rare naturally occurring radioactive element. It can be traced in tiny amounts in the uranium ores. About 100 micrograms (0.0001 grams) of polonium are found in one ton of uranium ore. Typically, this chemical is obtained as a radioactive decay product of uranium, thorium, and actinium. Polonium can also be synthesized by bombardment of bismuth-209 (a stable isotope) with neutrons in strictly controlled laboratory conditions. 

Commercially, polonium is isolated from by-products of the radium extraction process. Radium is first isolated from uranium mineral ores with the help of hydrochloric acid, after which the resulting residue solution is heated with hydrogen sulfide to precipitate polonium monosulfide (PoS). Pure polonium can also be obtained by electrolytic deposition, by bismuth or lead bombardment with neutrons, or with accelerated charged particles.

Polonium in Everyday Life

Element 84 can produce neutrons when alloyed with beryllium. In this form, polonium is used as a neutron source for alpha radiation. It’s also applied as a heat source and thermoelectric power source in satellites, as well as on the brushes for removing dust from photographic film. 

Industrially, polonium is used as an agent to eliminate static electricity generated by paper rolling, the spinning of synthetic fibers, or the manufacture of sheet plastics. 

How Dangerous Is Polonium?

Since polonium is classified as the most radioactive chemical element in the world, it’s extremely dangerous and may trigger severe health anomalies. 

The polonium-210 isotope is found in tobacco cigarettes. It’s one of the deadliest known toxins and a powerful carcinogen. Namely, only one microgram of this dangerous polonium isotope makes for a lethal dose, i.e. more than enough to kill the average adult. By inhaling it, a smoker (or even a passive smoker) is exposed to direct risk of lung cancer. After a long period of smoking, the smoker’s lungs become lined with a radioactive material and a toxic layer that may lead to various adverse health effects and tumors upon inner irradiation.

According to The Centers for Disease Control and Prevention (CDC), cigarettes and tobacco cause more harm to Americans each year than alcohol, suicide, AIDS, homicide, car accidents, and illegal drugs combined. This is due to the combination of many toxic and radioactive substances contained in tobacco cigarettes among which polonium-210 and lead-210 are the most dangerous and harmful ones. 

There are very few real-life cases of direct polonium poisoning, but there are a couple of high-profile ones. A well-known example of inner irradiation with a fatal outcome is the case of polonium poisoning of Alexander Litvinenko in London, a former officer of the Russian intelligence. Polonium poisoning was also suspected in the death of the Palestinian leader Yasser Arafat after surprisingly high levels of the radioactive polonium-210 isotope were detected on his clothes by a Swiss team of scientists. 

Environmental Effects of Polonium

Polonium is an extremely rare, naturally occurring radioactive element. Miniscule amounts of element 84 are mainly found in uranium ores. However, its occurrence in nature is not as hazardous as the plutonium-rich waste of the nuclear research laboratories is. 

The extremely high radioactivity of polonium poses an immense risk upon the environment, as well as upon all living forms in the environment. More specifically, 210Po may contaminate the vegetation, primarily originating from the decay of atmospheric radon-222 and absorption from the soil. On the other hand, the relatively short half-life of polonium-210 shortens the toxic exposure to this radioactive form of element 84. 

Isotopes of Polonium

There are 42 observed forms of polonium, which makes it a chemical element with the largest number of isotopes in the periodic table. All of the polonium isotopes are extremely radioactive. Polonium-210 is one of its forms that occur naturally, and with a half-life of 138.376 days, 210Po is the longest living natural isotope of element 84. 

The extremely toxic and radioactive isotope polonium-210 is an alpha emitter with a half-life of 138.4 days. 210Po isotope is typically manmade, i.e. produced synthetically through neutron bombardment of 209Bi in a nuclear reactor.

Among the radioisotopes, polonium-209 is the longest living synthetically produced form of polonium, with a half-life of 125.2 years. The polonium-20 and polonium-209 isotopes can be created by a proton bombardment of bismuth in a cyclotron. 

Main Isotopes of Polonium 

Iso­tope Decay
  abun­dance half-life (t1/2) mode pro­duct  
208Po syn 2.898 y α 204Pb  
β+ 208Bi  
209Po syn 125.2 y[1] α 205Pb  
β+ 209Bi  
210Po trace 138.376 d α 206Pb  

Source: Wikipedia

List of Polonium Compounds 

Almost all of the polonium compounds have been prepared for scientific research. No compounds contain element 84 with practical everyday use. The commonly exhibited oxidation states of polonium are +4 and +2. 

  • Polonium(IV) Thiocyanate
  • Polonium Dichloride
  • Polonium Hexafluoride
  • Polonium Monoxide
  • Polonium Tetrachloride
  • Polonium Dibromide
  • Polonium(IV) Sulfide
  • Polonium Hydride
  • Polonium Dioxide
  • Polonium Trioxide
  • Polonium(II) Phosphate
  • Polonium(IV) Hydrogen Sulfite
  • Polonium(IV) Hydrogen Sulfate

5 Interesting Facts and Explanations

  1. Polonium is considered to be the most radioactive chemical element. When the radiation excites the gas particles, this chemical element emits a blue glow. 
  2. The chalcogen family of the periodic table is classified in Group 16 (VIA). It consists of the chemical elements polonium, oxygen, sulfur, selenium, and tellurium. Polonium is the heaviest chalcogen element of this family of elements. 
  3. Element 84 has the largest number of identified forms (isotopes) among all other chemical elements. 
  4. The United States Nuclear Regulatory Commission estimates that only a few hundred grams of polonium are produced worldwide in a year.
  5. In the work Marie and Pierre Curie published on polonium in July 1898, they used the word ‘radioactivity’ for the first time in the history of science.