Polonium (Po)

Isotopes of Polonium

Isotope Atomic Mass Half-life Mode of Decay Nuclear Spin Nuclear Magnetic Moment
Po-206 205.98047 8.80 days EC to Bi-206;
α to Pb-202
0 No data available 
Po-207 206.98158 5.80 hours EC to Bi-207;
α to Pb-203
5/2 0.79
Po-208 207.98123 2.898 years EC to Bi-208;
α to Pb-204
0 No data available 
Po-209 208.982404 125.3 +/- 3.2 years EC to Bi-209;
α to Pb-205
1/2 1.77
Po-210 209.98286 138.38 days α to Pb-206 0 No data available 


Polonium was discovered in 1898 by Marie Sklodowska Curie. It is named for Poland, her birthplace.

Two crystalline forms of polonium exist: the alpha allotrope, with a simple cubic low-temperature form and a density of 9.196 g/cm3; and the beta modification, with a rhombohedral high-temperature form and a density of 9.398 g/cm3. Both allotropic forms coexist from 18-54 ºC and vaporize at 962 ºC. Polonium is practically insoluble in water and soluble in dilute mineral acids. At ordinary temperatures, it oxidizes slowly in air, forming its basic oxide. The metal dissolves in dilute hydrochloric acid, forming pink-red polonium. It dissolves in concentrated nitric acid and aqua regia, oxidizing to the Po4+ state.

Because of its radioactivity and alpha emission, polonium forms many types of radiolytic oxidation-reduction products. It is used on brushes to remove dusts from photographic film, as well as in instruments to eliminate static charges. It is also used as a small source to generate alpha particles and neutrons, and as a power source in devices where its radioactive decay energy is converted to electrical energy.

As with other radioactive substances, exposure to polonium's ionizing radiation can cause cancer. When ingested, it tends to accumulate in the liver, kidneys and spleen, causing radiation damage from the alpha particles. All operations and handling must be carried out by mechanical means, in leak-proof boxes, behind thick neutron shields.

Properties of Polonium

Name Polonium
Symbol Po
Atomic number 84
Atomic weight 209.0
Standard state Solid at 298 °K
CAS Registry ID 7440-08-6
Group in periodic table 16
Group name Chalcogen
Period in periodic table 6
Block in periodic table p-block
Color Silvery
Classification Metallic
Melting point 254 °C
Boiling point 962 °C
Thermal conductivity 20 (estimated) W/(m·K)
Electrical resistivity 40 x 10-8 Ω·m
Electronegativity 2.0
Heat of vaporization About 100 kJ·mol-1
Heat of fusion About 13 kJ·mol-1
Density of solid 9.20 g/cm(alpha form)
Electron configuration [Xe]4f145d106s26p4
Atomic radius 1.64 Å
Atomic volume 23.53 cm3/g-atom
Oxidation states  -2, 0, +2, +4, +6

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