Radon
Radon is a chemical element with symbol Rn and atomic number 86. It is a radioactive, colorless, odorless, tasteless noble gas, occurring naturally as a decay product of radium. Its most stable isotope, 222Rn, has a half-life of 3.8 days.
At a glance
- Atomic number
- 86
- Atomic mass
- 222 u
- Phase
- Gas
- Density
- 9.73 g/L
- Melting point
- 202 K
- Boiling point
- 211.5 K
- First ionization energy
- 1,037.1 kJ/mol
- Electronegativity
- 2.2
- Electron affinity
- -68 kJ/mol
- Molar heat capacity
- Unavailable
- Period
- 6
- Appearance
- colorless gas, occasionally glows green or red in discharge tubes
Conditions and isotopes affect measured properties. Some properties of short-lived elements are predicted. Electronegativity uses the Pauling scale.
Radon’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…
86 protons136 neutrons
Radon-222: 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 °FGas
At this temperature, radon is a gas.
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
RnNeutral atom · no charge
A neutral radon atom. Removing its first electron takes 1,037 kJ/mol.
Radon’s outer shell holds 8 electrons. Electron 9 is the first from an inner shell: it sits closer to the nucleus with less shielding, so removing it takes 1.5× 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 8 electrons before the first big jump are radon’s valence electrons: a full outer shell. That’s why radon sits in group 18 with the other noble gases, which all have full outer shells.
- Even the first electron is expensive: 1,037 kJ/mol. A full outer shell holds its electrons tightly, so noble gases have the highest first ionization energy in their row of the table, part of why they rarely react.
- 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 | 1,037 | – | Measured |
| 2 | 6 | 1,832 | 1.8 | Calculated |
| 3 | 6 | 2,837 | 1.5 | Estimated |
| 4 | 6 | 3,560 | 1.3 | Calculated |
| 5 | 6 | 5,104 | 1.4 | Calculated |
| 6 | 6 | 6,175 | 1.2 | Calculated |
| 7 | 6 | 8,491 | 1.4 | Calculated |
| 8 | 6 | 9,842 | 1.2 | Calculated |
| 9 | 5 | 14,859 | 1.5 | Calculated |
| 10 | 5 | 16,779 | 1.1 | Calculated |
| 11 | 5 | 18,815 | 1.1 | Calculated |
| 12 | 5 | 21,034 | 1.1 | Calculated |
| 13 | 5 | 23,156 | 1.1 | Calculated |
| 14 | 5 | 25,472 | 1.1 | Calculated |
| 15 | 5 | 28,270 | 1.1 | Calculated |
| 16 | 5 | 30,586 | 1.1 | Calculated |
| 17 | 5 | 32,998 | 1.1 | Calculated |
| 18 | 5 | 35,410 | 1.1 | Calculated |
| 19 | 5 | 47,085 | 1.3 | Calculated |
| 20 | 5 | 50,172 | 1.1 | Calculated |
| 21 | 5 | 53,067 | 1.1 | Calculated |
| 22 | 5 | 55,961 | 1.1 | Calculated |
| 23 | 5 | 61,751 | 1.1 | Calculated |
| 24 | 5 | 65,610 | 1.1 | Calculated |
| 25 | 5 | 73,329 | 1.1 | Calculated |
| 26 | 5 | 77,188 | 1.1 | Calculated |
| 27 | 4 | 82,013 | 1.1 | Calculated |
| 28 | 4 | 88,767 | 1.1 | Calculated |
| 29 | 4 | 94,556 | 1.1 | Calculated |
| 30 | 4 | 101,310 | 1.1 | Calculated |
| 31 | 4 | 107,099 | 1.1 | Calculated |
| 32 | 4 | 113,853 | 1.1 | Calculated |
| 33 | 4 | 120,607 | 1.1 | Calculated |
| 34 | 4 | 126,396 | 1 | Calculated |
| 35 | 4 | 134,115 | 1.1 | Calculated |
| 36 | 4 | 140,869 | 1.1 | Calculated |
| 37 | 4 | 146,658 | 1 | Calculated |
| 38 | 4 | 153,412 | 1 | Calculated |
| 39 | 4 | 160,166 | 1 | Calculated |
| 40 | 4 | 165,955 | 1 | Calculated |
| 41 | 4 | 196,155 | 1.2 | Calculated |
| 42 | 4 | 202,040 | 1 | Calculated |
| 43 | 4 | 208,215 | 1 | Calculated |
| 44 | 4 | 214,873 | 1 | Calculated |
| 45 | 4 | 221,241 | 1 | Calculated |
| 46 | 4 | 227,416 | 1 | Calculated |
| 47 | 4 | 238,029 | 1 | Calculated |
| 48 | 4 | 244,590 | 1 | Calculated |
| 49 | 4 | 251,441 | 1 | Calculated |
| 50 | 4 | 258,002 | 1 | Calculated |
| 51 | 4 | 284,053 | 1.1 | Calculated |
| 52 | 4 | 290,421 | 1 | Calculated |
| 53 | 4 | 297,368 | 1 | Calculated |
| 54 | 4 | 303,832 | 1 | Calculated |
| 55 | 4 | 331,234 | 1.1 | Calculated |
| 56 | 4 | 338,664 | 1 | Calculated |
| 57 | 4 | 356,899 | 1.1 | Calculated |
| 58 | 4 | 364,425 | 1 | Estimated |
| 59 | 3 | 595,218 | 1.6 | Calculated |
| 60 | 3 | 609,594 | 1 | Calculated |
| 61 | 3 | 624,839 | 1 | Calculated |
| 62 | 3 | 641,242 | 1 | Calculated |
| 63 | 3 | 656,776 | 1 | Calculated |
| 64 | 3 | 671,924 | 1 | Calculated |
| 65 | 3 | 702,703 | 1 | Calculated |
| 66 | 3 | 718,816 | 1 | Calculated |
| 67 | 3 | 736,183 | 1 | Calculated |
| 68 | 3 | 752,586 | 1 | Calculated |
| 69 | 3 | 796,969 | 1.1 | Calculated |
| 70 | 3 | 811,442 | 1 | Calculated |
| 71 | 3 | 826,879 | 1 | Calculated |
| 72 | 3 | 840,387 | 1 | Calculated |
| 73 | 3 | 927,224 | 1.1 | Calculated |
| 74 | 3 | 943,627 | 1 | Calculated |
| 75 | 3 | 976,432 | 1 | Calculated |
| 76 | 3 | 992,834 | 1 | Calculated |
| 77 | 2 | 2,100,486 | 2.1 | Calculated |
| 78 | 2 | 2,138,115 | 1 | Calculated |
| 79 | 2 | 2,180,569 | 1 | Calculated |
| 80 | 2 | 2,218,198 | 1 | Calculated |
| 81 | 2 | 2,538,529 | 1.1 | Calculated |
| 82 | 2 | 2,588,701 | 1 | Calculated |
| 83 | 2 | 2,652,382 | 1 | Calculated |
| 84 | 2 | 2,692,240 | 1 | Calculated |
| 85 | 1 | 10,695,042 | 4 | Calculated |
| 86 | 1 | 10,887,617 | 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
Radon is a gas made in rocks and soil wherever uranium decays. Being a gas, it can seep into buildings, where it builds up in poorly ventilated basements.
Half of any sample of Rn-222 decays every 3.82 days, turning into Po-218.
Half-lives passed (1 half-life = 3.82 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 Po-218 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
0.00973 g/cm³11th lowest of 99
Melting point
202 K10th lowest of 96
Boiling point
212 K10th lowest of 97
Electronegativity
2.222nd highest of 96
First ionization energy
1,037 kJ/mol13th 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.
- RadonRoyal Society of Chemistry
- RadonWikipedia
- Quantum numbers and electron configurationsPurdue
- Hydrogenic wavefunctionsNIST
- Ionization energiesNIST Atomic Spectra Database