Category: Noble gas
Atomic Number: 36
Period: 4 | Group: 18
Block: p-block
Named "hidden", used to define the metre, and briefly the fictional weakness of a superhero.
| Property | Value |
|---|---|
| Phase at STP | Gas |
| Density | N/A |
| Melting Point | 115.79 K (-157.36 °C) |
| Boiling Point | 119.93 K (-153.22 °C) |
| Heat Capacity | N/A |
| Property | Value |
|---|---|
| Atomic Mass | 83.7980 u |
| Electronegativity (Pauling) | N/A |
| Oxidation States | 0, +2 |
| Electron Configuration |
| Discovered By | Unknown |
|---|---|
| Discovery Year | 1898 |
| Named After | Greek kryptos, "hidden" |
Searching the air (1898)
After argon was found in 1894 and helium in 1895, William Ramsay suspected that more unknown gases were hidden in the air. On 30 May 1898, he and his assistant Morris Travers, at University College London, slowly evaporated a sample of liquefied air and examined the last gas that remained.
A hidden element
Its spectrum showed bright yellow and green lines that belonged to no known element. They named it krypton, from the Greek kryptos, meaning hidden. Within weeks they found neon and xenon in the same way.
Krypton and the meter
In 1960 the General Conference on Weights and Measures redefined the meter using light from krypton-86, replacing the platinum-iridium prototype bar. In 1983 the krypton definition was replaced by one based on the speed of light.
| ISOTOPE | Neutrons | Natural Abundance | Half-life | Decay Mode |
|---|---|---|---|---|
| Kr-78 | 42 | 0.355% | Stable | - |
| Kr-80 | 44 | 2.286% | Stable | - |
| Kr-82 | 46 | 11.593% | Stable | - |
| Kr-83 | 47 | 11.500% | Stable | - |
| Kr-84 | 48 | 56.987% | Stable | - |
| Kr-85 | 49 | - | 10.739 yrs | β⁻ |
| Kr-86 | 50 | 17.279% | Stable | - |
Data: IAEA Nuclear Data Section, LiveChart of Nuclides, ground-state evaluations, retrieved October 10, 2026. Abundance is the share of atoms in the natural element; a dash means the isotope has no standard natural abundance.
Lighting
Lamps: krypton is used in some fluorescent tubes and in premium incandescent and halogen bulbs, where its heavy atoms slow the evaporation of the tungsten filament.
Flash lamps: krypton gives an intense white light in photographic flashes and in lamps that pump some lasers.
Insulating windows
Krypton fills the gap between the panes of some high-performance double and triple glazing. It conducts heat less than argon, so a thinner gap gives the same insulation.
Lasers, space and science
Excimer lasers: krypton fluoride lasers emit ultraviolet light at 248 nm, used in chip-making lithography and in fusion research.
Electric propulsion: some satellite thrusters, including those of SpaceX's first-generation Starlink satellites, use krypton as a cheaper propellant than xenon.
Length standard: from 1960 to 1983 the meter was defined as 1,650,763.73 wavelengths of an orange-red spectral line of krypton-86.
| Earth's Crust | N/A |
|---|---|
| Universe | N/A |