ElementsWhat is krypton?
Krypton is a rare gas found in tiny amounts in air. It almost never reacts with other elements.
What is krypton used for?
Some bright and long-life lamps, lasers, and filling the gap in high-quality insulated windows.
Where the name comes from
From the Greek word kryptos, hidden.
Key facts
- Symbol
- Kr
- Atomic number
- 36
- Atomic mass
- 83.80 u
- Family
- Noble gas
- Period
- 4
- Group
- 18
- Block
- p
- State at room temperature
- Gas
- Melting point
- -157.4 °C (115.79 K, -251 °F)
- Boiling point
- -153.2 °C (119.93 K, -244 °F)
- Density
- 0.003733 g/cm³ (as a gas at 0 °C)
- Electrons per shell
- 2, 8, 18, 8
- Electron configuration
- [Ar]4s2 3d10 4p6
- Common oxidation states
- 0
- Electronegativity (Pauling)
- 3
- First ionisation energy
- 14 eV
- Electron affinity
- no value
- Atomic radius (van der Waals)
- 202 pm
- Discovered
- 1898
Place in the periodic table
Krypton is element number 36. It sits in period 4 (row 4) of the periodic table, in group 18 (column 18), and belongs to the p-block. Just before it comes bromine (35), and just after it comes rubidium (37). In the same column, argon is above it and xenon is below it. Elements in one column tend to behave alike.
Family: Noble gases.
Physical properties
At room temperature krypton is a gas. It melts at -157.4 °C and boils at -153.2 °C, so it stays liquid over a range of 4 degrees. One litre of the gas weighs about 3.733 grams at 0 °C and normal pressure. That is heavier than air, which weighs about 1.29 grams a litre. It has the 8th lowest melting point of all elements.
Inside the atom
An atom of krypton has 36 protons in its nucleus and, when neutral, 36 electrons around it. The electrons are arranged in 4 shells: 2, 8, 18, 8. The outermost shell holds 8 electrons. Written in full, the electron configuration is [Ar]4s2 3d10 4p6.
Its electronegativity on the Pauling scale is 3. This number shows how strongly an atom pulls shared electrons towards itself: fluorine, the strongest, is 3.98. Removing one electron from an atom takes 14 electronvolts (about 1,351 kilojoules per mole). One mole of krypton weighs 83.80 grams, so a single gram contains about 7.19 × 1021 atoms.
The ring picture is a simple model that only counts the electrons in each shell. Real atoms do not look like this.
Next steps
- Work out the weight of a compound that contains krypton with the molar mass calculator.
- Compare it with every other element in the sortable list.
- Test yourself with the symbol quiz.
Figures on this page are from PubChem (U.S. National Library of Medicine), as downloaded on 11 November 2026. See About and data sources.