Krypton (Kr)
Element 36 · Noble gas · atomic mass 83.798 u · group 18, period 4
Electron shells: 2, 8, 18, 8
Krypton is a rare noble gas used where a very bright, very white light is needed. For 23 years the metre itself was defined by a krypton-86 spectral line.
From 1960 to 1983, one metre was officially defined by the wavelength of krypton-86 light.
- Atomic number
- 36
- Atomic mass
- 83.798 u
- Electron configuration
- [Ar] 4s² 3d¹⁰ 4p⁶
- Group · period · block
- 18 · 4 · p
- Oxidation states
- 0
- Electronegativity
- 3 (Pauling)
- Melting point
- -157 °C
- Boiling point
- -153 °C
- Density
- 0.003733 g/cm³
- State at 20 °C
- Gas
- Appearance
- Colourless gas
- Discovered
- William Ramsay and Morris Travers, 1898
36 protons, and 36 electrons when neutral
IUPAC standard atomic weight
Noble gases
What Krypton is used for
- High-performance lighting and flash lamps
- Insulating gas in windows
- Excimer lasers
- High-speed photography
Atomic structure of Krypton
A neutral krypton atom has 36 protons and 36 electrons. Its most common isotope carries about 48 neutrons, which is where the mass number 84 comes from. Change the neutron count and you have a different isotope of krypton; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 18, 8. In orbital notation that is [Ar] 4s² 3d¹⁰ 4p⁶, leaving 8 valence electrons in the outer shell — the ones that do the chemistry.
3D electron orbitals
See where Krypton's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Krypton 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
Krypton was discovered by William Ramsay and Morris Travers in 1898. Its name comes from Greek kryptos, "hidden".
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 Krypton?
The standard atomic weight of Krypton is 83.798 u, as published by IUPAC's Commission on Isotopic Abundances and Atomic Weights.
How many protons, neutrons and electrons does Krypton have?
Krypton has 36 protons, because the atomic number is the proton count and that is what makes an atom Krypton at all. A neutral Krypton atom has the same number of electrons, 36. The neutron count varies by isotope; the most common one has about 48, since 84 − 36 = 48.
What is the electron configuration of Krypton?
The electron configuration of Krypton is [Ar] 4s² 3d¹⁰ 4p⁶. Its electrons are arranged 2, 8, 18, 8 across 4 shells.
Is Krypton a metal?
No. Krypton 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 Krypton in?
Krypton is in group 18 (the noble gases), period 4, in the p-block. The group is its column and the period is its row.
What is the melting point of Krypton?
Krypton melts at -157 °C and boils at -153 °C. That puts it in the gases at everyday temperatures.
What is Krypton used for?
High-performance lighting and flash lamps, Insulating gas in windows, Excimer lasers, High-speed photography. Krypton is a rare noble gas used where a very bright, very white light is needed.
Who discovered Krypton, and where does its name come from?
Krypton (Kr) was discovered by William Ramsay and Morris Travers in 1898. The name comes from Greek kryptos, "hidden".