Xenon (Xe)
Element 54 · Noble gas · atomic mass 131.29 u · group 18, period 5
Electron shells: 2, 8, 18, 18, 8
Xenon was the noble gas that broke the rule that noble gases do not react. It is also a general anaesthetic and an efficient ion-thruster propellant.
The first noble-gas compound, xenon hexafluoroplatinate, overturned textbook chemistry in 1962.
- Atomic number
- 54
- Atomic mass
- 131.29 u
- Electron configuration
- [Kr] 5s² 4d¹⁰ 5p⁶
- Group · period · block
- 18 · 5 · p
- Oxidation states
- 0, +2, +4, +6
- Electronegativity
- 2.6 (Pauling)
- Melting point
- -112 °C
- Boiling point
- -108 °C
- Density
- 0.005887 g/cm³
- State at 20 °C
- Gas
- Appearance
- Colourless gas
- Discovered
- William Ramsay and Morris Travers, 1898
54 protons, and 54 electrons when neutral
IUPAC standard atomic weight
Noble gases
What Xenon is used for
- Ion thrusters for spacecraft
- High-intensity headlamps and flash lamps
- General anaesthesia
- Dark-matter and neutrino detectors
Atomic structure of Xenon
A neutral xenon atom has 54 protons and 54 electrons. Its most common isotope carries about 77 neutrons, which is where the mass number 131 comes from. Change the neutron count and you have a different isotope of xenon; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 18, 18, 8. In orbital notation that is [Kr] 5s² 4d¹⁰ 5p⁶, leaving 8 valence electrons in the outer shell — the ones that do the chemistry.
3D electron orbitals
See where Xenon's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Xenon sits in the periodic table
Group 18, with full outer shells and almost no drive to react. Their inertness is exactly what makes them useful for shielding, lighting and cooling.
Discovery and naming
Xenon was discovered by William Ramsay and Morris Travers in 1898. Its name comes from Greek xenos, "stranger".
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Xenon?
The standard atomic weight of Xenon is 131.29 u, as published by IUPAC's Commission on Isotopic Abundances and Atomic Weights.
How many protons, neutrons and electrons does Xenon have?
Xenon has 54 protons, because the atomic number is the proton count and that is what makes an atom Xenon at all. A neutral Xenon atom has the same number of electrons, 54. The neutron count varies by isotope; the most common one has about 77, since 131 − 54 = 77.
What is the electron configuration of Xenon?
The electron configuration of Xenon is [Kr] 5s² 4d¹⁰ 5p⁶. Its electrons are arranged 2, 8, 18, 18, 8 across 5 shells.
Is Xenon a metal?
No. Xenon is classified as a noble gas, on the right-hand side of the table where elements gain or share electrons rather than losing them.
What group and period is Xenon in?
Xenon is in group 18 (the noble gases), period 5, in the p-block. The group is its column and the period is its row.
What is the melting point of Xenon?
Xenon melts at -112 °C and boils at -108 °C. That puts it in the gases at everyday temperatures.
What is Xenon used for?
Ion thrusters for spacecraft, High-intensity headlamps and flash lamps, General anaesthesia, Dark-matter and neutrino detectors. Xenon was the noble gas that broke the rule that noble gases do not react.
Who discovered Xenon, and where does its name come from?
Xenon (Xe) was discovered by William Ramsay and Morris Travers in 1898. The name comes from Greek xenos, "stranger".