Xenon (Xe)
Xenon (Xe) is a noble gas with atomic number 54 and a standard atomic weight of 131.29. At room temperature it is a gas that melts at -112 °C and boils at -108 °C.
Xenon key facts
Xenon at a glance
Identity
| Symbol | Xe |
|---|---|
| Atomic number (Z) | 54 |
| Atomic weight | 131.29 ± 0.01 (CIAAW 2024) |
| Category | Noble gas |
| Group | 18 — noble gases |
| Period | 5 |
| Block | p-block |
| CAS number | 7440-63-3 |
Atomic properties
| Electron configuration | [Kr] 4d10 5s2 5p6 Full: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 |
|---|---|
| Electrons per shell | 2, 8, 18, 18, 8 |
| Oxidation states | +2, +4, +6 Less common: +8 |
| Electronegativity (Pauling) | 2.6 |
| First ionisation energy | 12.13 eV (1,170.3 kJ/mol) 2nd: 20.975 eV · 3rd: 31.05 eV |
| Covalent radius | 131 pm |
| Van der Waals radius | 216 pm |
Physical properties
| State at 25 °C | Gas |
|---|---|
| Melting point | -111.7 °C · -169.1 °F · 161.4 K |
| Boiling point | -108.1 °C · -162.6 °F · 165.05 K |
| Density | 5.894 g/L (gas at 0 °C, 1 atm) |
| Specific heat capacity | 0.158 J/(g·K) |
| Thermal conductivity | 0.006 W/(m·K) |
| Crystal structure | Face-centred cubic |
Isotopes & abundance
| Natural occurrence | Primordial |
|---|---|
| Radioactive | No |
| Natural isotopes (abundance) | 132Xe 26.909%, 129Xe 26.401%, 131Xe 21.232%, 134Xe 10.436%, 136Xe 8.857% (radioactive), 130Xe 4.071% |
| Stable isotopes | 8 |
| Known isotopes | 43 |
| Abundance in Earth's crust | 0.00003 mg/kg |
| Abundance in seawater | 0.00005 mg/L |
Atomic weights: CIAAW Abridged Standard Atomic Weights 2024. Other properties: standard reference compilations, checked October 2026; predicted values are marked.
Xenon electron configuration
Xenon has 54 electrons. Written in short form, its ground-state configuration is [Kr] 4d10 5s2 5p6 — the electrons of the noble gas krypton, plus 4d10 5s2 5p6.Written out in full: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6.
As a member of group 18 it has 8 valence electrons in its outer shell (shell 5), which largely decide its chemistry — a full outer shell, which is why it is so unreactive.
Discovery and name
1898 — William Ramsay and Morris Travers · England.
Greek xenos, stranger.
Known for
Used in car headlamps, flash lamps and ion thrusters for spacecraft; also as a general anaesthetic and in medical imaging.
Isotopes of xenon
Naturally occurring xenon is a mix of 9 isotopes. Each has 54 protons; they differ in the number of neutrons:
| Isotope | Protons | Neutrons | Natural abundance | Stability |
|---|---|---|---|---|
| 132Xe | 54 | 78 | 26.909% | stable |
| 129Xe | 54 | 75 | 26.401% | stable |
| 131Xe | 54 | 77 | 21.232% | stable |
| 134Xe | 54 | 80 | 10.436% | stable |
| 136Xe | 54 | 82 | 8.857% | radioactive · half-life 2.18 × 10²¹ years |
| 130Xe | 54 | 76 | 4.071% | stable |
| 128Xe | 54 | 74 | 1.91% | stable |
| 124Xe | 54 | 70 | 0.095% | stable |
| 126Xe | 54 | 72 | 0.089% | stable |
43 isotopes of xenon are known in our data set (half-lives as published in nuclear data tables).
Xenon compared with group 18
The other elements in group 18 (noble gases), from top to bottom of the table:
| Element | Z | Atomic weight | Melting point | Boiling point | Density | Electronegativity |
|---|---|---|---|---|---|---|
| Helium | 2 | 4.0026 | — | -269 °C | 0.1786 g/L | — |
| Neon | 10 | 20.180 | -249 °C | -246 °C | 0.9002 g/L | — |
| Argon | 18 | 39.95 | -189 °C | -186 °C | 1.784 g/L | — |
| Krypton | 36 | 83.798 | -157 °C | -153 °C | 3.749 g/L | 3 |
| Xenon | 54 | 131.29 | -112 °C | -108 °C | 5.894 g/L | 2.6 |
| Radon | 86 | [222] | -71 °C | -62 °C | 9.73 g/L | 2.2 |
| Oganesson | 118 | [294] | — | — | 7 g/cm³ (pred.) | — |