Polonium
Polonium is a chemical element with symbol Po and atomic number 84, discovered in 1898 by Marie Curie and Pierre Curie. A rare and highly radioactive element with no stable isotopes, polonium is chemically similar to bismuth and tellurium, and it occurs in uranium ores. Applications of polonium are few.
At a glance
- Atomic number
- 84
- Atomic mass
- 209 u
- Phase
- Solid
- Density
- 9.196 g/cm³
- Melting point
- 527 K
- Boiling point
- 1,235 K
- First ionization energy
- 812.2 kJ/mol
- Electronegativity
- 2
- Electron affinity
- 136 kJ/mol
- Molar heat capacity
- 26.4 J/(mol·K)
- Period
- 6
- Appearance
- silvery
Conditions and isotopes affect measured properties. Some properties of short-lived elements are predicted. Electronegativity uses the Pauling scale.
Polonium’s orbitals use a hydrogen-like approximation. Every orbital of each visible subshell is shown: in Shapes as the surface holding half its probability, with light and dark shades for opposite signs of the wavefunction; in Cloud as dots where its electrons are likely to be. Sizes are stepped by shell, like the Shell model.
54 is the [Xe] core total across five shells.
Preparing the orbital view…
84 protons125 neutrons
Polonium-209: its most common form in nature, or its longest-lived if it has none. The nucleus is drawn far too big: it’s about 100,000 times smaller than the atom.
Turn up the heat
A step of 1 K is the same size as 1 °C, so the two scales are always 273.15 apart. Fahrenheit is different: its degrees are smaller and it starts elsewhere, so water freezes at 273.15 K, 0 °C and 32 °F.25 °C · 77 °FSolid
At this temperature, polonium is a solid.
At normal atmospheric pressure (1 atm). The temperature scale is logarithmic. The particle box is schematic: real samples hold vastly more atoms, and spacing and speeds are not to scale.
Pull the electrons off
PoNeutral atom · no charge
A neutral polonium atom. Removing its first electron takes 812 kJ/mol.
Polonium’s outer shell holds 6 electrons. Electron 7 is the first from an inner shell: it sits closer to the nucleus with less shielding, so removing it takes 1.6× as much energy as the one before. Each dashed line on the chart marks another jump, into a shell even closer to the nucleus.
What does this tell us?
- The 6 electrons before the first big jump are polonium’s valence electrons, the ones it uses in chemical reactions. That’s why polonium sits in group 16: every element in the group has the same number of outer electrons, so they react in similar ways.
- Within a shell the steps rise gently. Each electron removed leaves fewer electrons pushing the others away, while the nucleus pulls just as hard, so the next one is held a little more tightly.
Show the values as a table
| Electron | Shell | Energy (kJ/mol) | × previous | Value |
|---|---|---|---|---|
| 1 | 6 | 812 | – | Measured |
| 2 | 6 | 1,862 | 2.3 | Estimated |
| 3 | 6 | 2,634 | 1.4 | Estimated |
| 4 | 6 | 3,474 | 1.3 | Calculated |
| 5 | 6 | 5,500 | 1.6 | Calculated |
| 6 | 6 | 6,667 | 1.2 | Calculated |
| 7 | 5 | 10,420 | 1.6 | Calculated |
| 8 | 5 | 12,061 | 1.2 | Calculated |
| 9 | 5 | 14,097 | 1.2 | Calculated |
| 10 | 5 | 16,017 | 1.1 | Calculated |
| 11 | 5 | 17,946 | 1.1 | Calculated |
| 12 | 5 | 20,165 | 1.1 | Calculated |
| 13 | 5 | 22,674 | 1.1 | Calculated |
| 14 | 5 | 24,797 | 1.1 | Calculated |
| 15 | 5 | 27,112 | 1.1 | Calculated |
| 16 | 5 | 29,332 | 1.1 | Calculated |
| 17 | 5 | 40,138 | 1.4 | Calculated |
| 18 | 5 | 42,839 | 1.1 | Calculated |
| 19 | 5 | 45,638 | 1.1 | Calculated |
| 20 | 5 | 48,436 | 1.1 | Calculated |
| 21 | 5 | 54,032 | 1.1 | Calculated |
| 22 | 5 | 56,926 | 1.1 | Calculated |
| 23 | 5 | 64,645 | 1.1 | Calculated |
| 24 | 5 | 67,540 | 1 | Calculated |
| 25 | 4 | 71,399 | 1.1 | Calculated |
| 26 | 4 | 77,188 | 1.1 | Calculated |
| 27 | 4 | 83,942 | 1.1 | Calculated |
| 28 | 4 | 89,731 | 1.1 | Calculated |
| 29 | 4 | 95,520 | 1.1 | Calculated |
| 30 | 4 | 102,274 | 1.1 | Calculated |
| 31 | 4 | 108,064 | 1.1 | Calculated |
| 32 | 4 | 113,853 | 1.1 | Calculated |
| 33 | 4 | 120,607 | 1.1 | Calculated |
| 34 | 4 | 127,361 | 1.1 | Calculated |
| 35 | 4 | 133,150 | 1 | Calculated |
| 36 | 4 | 138,939 | 1 | Calculated |
| 37 | 4 | 145,693 | 1 | Calculated |
| 38 | 4 | 151,482 | 1 | Calculated |
| 39 | 4 | 179,945 | 1.2 | Calculated |
| 40 | 4 | 185,541 | 1 | Calculated |
| 41 | 4 | 191,620 | 1 | Calculated |
| 42 | 4 | 197,988 | 1 | Calculated |
| 43 | 4 | 204,066 | 1 | Calculated |
| 44 | 4 | 210,049 | 1 | Calculated |
| 45 | 4 | 220,083 | 1 | Calculated |
| 46 | 4 | 226,258 | 1 | Calculated |
| 47 | 4 | 232,916 | 1 | Calculated |
| 48 | 4 | 239,284 | 1 | Calculated |
| 49 | 4 | 264,370 | 1.1 | Calculated |
| 50 | 4 | 270,448 | 1 | Calculated |
| 51 | 4 | 277,202 | 1 | Calculated |
| 52 | 4 | 283,474 | 1 | Calculated |
| 53 | 4 | 308,174 | 1.1 | Calculated |
| 54 | 4 | 315,314 | 1 | Calculated |
| 55 | 4 | 332,874 | 1.1 | Calculated |
| 56 | 4 | 340,034 | 1 | Estimated |
| 57 | 3 | 558,168 | 1.6 | Calculated |
| 58 | 3 | 572,158 | 1 | Calculated |
| 59 | 3 | 587,017 | 1 | Calculated |
| 60 | 3 | 602,840 | 1 | Calculated |
| 61 | 3 | 617,989 | 1 | Calculated |
| 62 | 3 | 632,654 | 1 | Calculated |
| 63 | 3 | 661,503 | 1 | Calculated |
| 64 | 3 | 676,845 | 1 | Calculated |
| 65 | 3 | 693,826 | 1 | Calculated |
| 66 | 3 | 709,167 | 1 | Calculated |
| 67 | 3 | 753,550 | 1.1 | Calculated |
| 68 | 3 | 767,058 | 1 | Calculated |
| 69 | 3 | 781,531 | 1 | Calculated |
| 70 | 3 | 795,039 | 1 | Calculated |
| 71 | 3 | 873,192 | 1.1 | Calculated |
| 72 | 3 | 889,595 | 1 | Calculated |
| 73 | 3 | 921,435 | 1 | Calculated |
| 74 | 3 | 936,873 | 1 | Calculated |
| 75 | 2 | 1,994,352 | 2.1 | Calculated |
| 76 | 2 | 2,031,016 | 1 | Calculated |
| 77 | 2 | 2,071,540 | 1 | Calculated |
| 78 | 2 | 2,109,169 | 1 | Calculated |
| 79 | 2 | 2,398,625 | 1.1 | Calculated |
| 80 | 2 | 2,446,868 | 1 | Calculated |
| 81 | 2 | 2,507,654 | 1 | Calculated |
| 82 | 2 | 2,546,287 | 1 | Calculated |
| 83 | 1 | 10,137,164 | 4 | Calculated |
| 84 | 1 | 10,322,329 | 1 | Calculated |
Successive ionization energies of gas-phase atoms and ions from the NIST Atomic Spectra Database. Solid bars are measured; hatched bars were estimated from nearby measurements or calculated from quantum theory, as is usual for highly charged ions. Electrons are taken from the outermost shell first, a simplification: electrons in different subshells of the same shell also differ in energy. On the log scale each gridline is 10 times the one below.
Watching atoms decay
Polonium appears three times in uranium-238’s chain. Marie Curie discovered it in 1898 and named it after her native Poland.
Half of any sample of Po-210 decays every 138 days, turning into Pb-206.
Half-lives passed (1 half-life = 138 days)
No time passed · 0 half-lives · 100 of 100 atoms left
Each atom decays at a random moment, so no one can say which will go next, but about half of whatever is left goes in every half-life. The dashed curve is the prediction; the solid line is this sample. The new Pb-206 atoms decay too, on their own schedule, which the chain below follows.
From U-238 to stable Pb-206: 14 steps
- U-238Uranium4.5 billion yearsαdecays by alpha
- Th-234Thorium24 daysβdecays by beta
- Pa-234mProtactinium1.2 minutesβdecays by beta
- U-234Uranium250,000 yearsαdecays by alpha
- Th-230Thorium75,000 yearsαdecays by alpha
- Ra-226Radium1,600 yearsαdecays by alpha
- Rn-222Radon3.8 daysαdecays by alpha
- Po-218Polonium3.1 minutesαdecays by alpha
- Pb-214Lead27 minutesβdecays by beta
- Bi-214Bismuth20 minutesβdecays by beta
- Po-214Polonium160 microsecondsαdecays by alpha
- Pb-210Lead22 yearsβdecays by beta
- Bi-210Bismuth5 daysβdecays by beta
- Po-210Polonium140 daysαdecays by alpha
- Pb-206Leadstable
Arrows show how each atom decays: α gives off an alpha particle (2 protons and 2 neutrons), β turns a neutron into a proton, γ gives off a gamma ray.
Half-lives and decay modes from the IAEA Live Chart of Nuclides (evaluated ENSDF data). The chain follows each atom’s most common decay; a few steps have rare side branches.
How does it compare?
Density
9.2 g/cm³31st highest of 99
Melting point
527 K26th lowest of 96
Boiling point
1,235 K26th lowest of 97
Electronegativity
232nd highest of 96
First ionization energy
812 kJ/mol30th highest of 99
Elements 1–99 from the reference data; heavier elements are left out because only a few atoms have ever been made, so their bulk properties are predictions. First ionization energies come from NIST. Density uses a logarithmic scale, because gases are around a thousand times less dense than solids; gas densities are at 0 °C and 1 atm. Melting and boiling points are at normal pressure. Everyday temperatures and light sources in the pictures are approximate. Hover over a dot to see the element, or click it to compare.
Keep exploring
Explore the stories, imagery, and reference data in more depth. Properties with no value in the reference are marked unavailable.
- PoloniumRoyal Society of Chemistry
- PoloniumWikipedia
- Quantum numbers and electron configurationsPurdue
- Hydrogenic wavefunctionsNIST
- Ionization energiesNIST Atomic Spectra Database