Krypton
Atomic Data
| Atomic Number | 36 |
| Symbol | Kr |
| Atomic Weight | 83.798 u |
| Density (STP) | 3.749 g/L |
| Melting Point | −157.36 °C (115.79 K) |
| Boiling Point | −153.22 °C (119.93 K) |
| Electronegativity | : |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 |
| Oxidation States | 0, +2 |
| Phase at STP | Gas |
| Category | Noble Gas |
| Period / Group | 4 / 18 |
| CAS Number | 7439-90-9 |
Electron Configuration
[Ar] 3d10 4s2 4p6
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 6 | 18 |
| M | 3 | 3d | 10 | 28 |
| N | 4 | 4s | 2 | 30 |
| N | 4 | 4p | 6 | 36 |
| Total | 36 | 36 | ||
Isotopes of Krypton
Krypton has six naturally occurring stable isotopes. The most abundant is ⁸⁴Kr, comprising 56.987% of all naturally occurring Krypton.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Krypton-78 | ⁷⁸Kr | 36 | 42 | 0.355 | Stable |
| Krypton-80 | ⁸⁰Kr | 36 | 44 | 2.286 | Stable |
| Krypton-82 | ⁸²Kr | 36 | 46 | 11.593 | Stable |
| Krypton-83 | ⁸³Kr | 36 | 47 | 11.5 | Stable |
| Krypton-84 | ⁸⁴Kr | 36 | 48 | 56.987 | Stable |
| Krypton-86 | ⁸⁶Kr | 36 | 50 | 17.279 | Stable |
Abundance & Occurrence
Krypton is present in Earth's crust at approximately 0.0001 ppm by mass and at approximately 4 ppm by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Asphyxiation: Krypton is a colourless, odourless inert gas; it is denser than air and can accumulate in low-lying confined spaces, displacing oxygen to dangerous levels without warning.
- Pressurised cylinders: Krypton is stored under high pressure; cylinders must be secured, kept away from heat, and used with appropriate regulators.
- Krypton-85 radiation: Kr-85, a radioactive isotope released during nuclear fuel reprocessing, is a low-energy beta emitter; environmental releases are regulated and monitored as part of nuclear facility licensing.
- Liquid krypton: Liquid krypton at −153 °C causes cryogenic burns on direct skin contact; rapid vaporisation in confined spaces creates an asphyxiation risk.
Krypton in the Real World
Real-World Uses
- Energy-efficient lighting: Krypton gas filling incandescent bulbs suppresses tungsten filament evaporation better than argon, allowing brighter operation at the same power or the same brightness at lower power, improving lamp efficiency.
- Excimer lasers: Krypton fluoride (KrF) excimer lasers (248 nm UV) are used in deep-UV lithography to pattern semiconductor chips at sub-300 nm feature sizes, and in refractive eye surgery (LASEK).
- Scientific metrology: Between 1960 and 1983, the metre was officially defined as 1,650,763.73 wavelengths of the orange-red light emitted by krypton-86, establishing a reproducible physical standard for length.
- Flash photography: Krypton gas fills high-speed photographic flash lamps used in professional studio strobes and stroboscopic measurement equipment, providing a bright, short-duration pulse of white light.
- Nuclear waste tracking: Krypton-85 (t½ = 10.76 yr) released from nuclear fuel reprocessing is monitored globally as an indicator of undeclared nuclear activities, serving as a non-proliferation treaty verification tool.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
What is krypton used for?
Krypton is used mainly in lighting. Krypton-filled incandescent bulbs burn brighter and last longer than argon-filled ones because krypton better suppresses tungsten filament evaporation. Krypton fluoride lasers produce intense ultraviolet light used in lithography for semiconductor manufacturing. Radioactive krypton-85 is used in leak-detection testing of sealed devices.
Is krypton safe?
Krypton is a chemically inert noble gas and is non-toxic. Like other noble gases at high concentrations, it can act as a simple asphyxiant by displacing oxygen. Krypton-85, a radioactive isotope released during nuclear fuel reprocessing, is a low-level radiation source monitored in the environment, though it contributes minimally to public dose.
How was krypton discovered?
Krypton was discovered in 1898 by British scientists William Ramsay and Morris Travers by fractional distillation of liquid air. It was one of three noble gases discovered that year (along with neon and xenon). The name comes from the Greek 'kryptos', meaning hidden: the same root as 'crypt' and, much later, the fictional planet Krypton of Superman fame.
What is the significance of krypton in metrology?
From 1960 to 1983, the international definition of the metre was based on krypton: one metre was defined as exactly 1,650,763.73 wavelengths of the orange-red emission line of krypton-86 in vacuum. This definition replaced the physical platinum-iridium metre bar and provided a universal, reproducible standard. The metre is now defined in terms of the speed of light.