Krypton
Element 36 · Noble Gas
Krypton is a colorless, odorless noble gas with a full outer shell ([Ar] 3d10 4s2 4p6), making it almost completely unreactive — only a handful of compounds such as krypton difluoride exist, and only under extreme conditions.
Its inertness is its virtue: sealed inside lamps it gives an intense white light without reacting with the filament, and in windows it insulates better than air. Krypton-86 once held a unique honor — its orange-red spectral line defined the international standard meter for over two decades.
Key facts
| Atomic number | 36 |
|---|---|
| Atomic weight | 83.798 |
| Category | Noble Gas |
| Group / Period | 18 / 4 |
| Block | p |
| Electron configuration | [Ar] 3d10 4s2 4p6 |
| Common oxidation states | 0, +2 |
| State at STP | Gas |
| Electronegativity | 3.00 |
| Atomic radius | 88 pm |
| Density | 3.749 g/L (gas) |
| Melting point | -157.36 °C |
| Boiling point | -153.22 °C |
Occurrence
Krypton makes up about one part per million of Earth's atmosphere and is obtained by fractional distillation of liquid air. Its name comes from the Greek kryptos, meaning hidden, because Ramsay and Travers had to hunt carefully to isolate it in 1898.
Applications
High-intensity photographic flash lamps and airport runway lights use krypton
Krypton fluoride excimer lasers etch microchips and treat eyes
Double-glazed windows are filled with krypton for thermal insulation
Experimental ion thrusters for spacecraft use krypton propellant
Lighting research uses krypton's bright spectral lines
Common compounds
- krypton difluoride
- krypton clathrates
From 1960 to 1983, the meter was officially defined by the orange-red glow of krypton-86.
Data source: IUPAC standard atomic weights 2021