Krypton is a colorless, odorless noble gas found in trace amounts in Earth’s atmosphere (~1 ppm). It is chemically inert, forms few compounds (e.g., KrF₂), and is used in lighting and specialized lasers.
Krypton has a closed-shell configuration \([Ar]3d^{10}\,4s^2\,4p^6\). The filled valence shell (octet) gives it a very high ionization energy and negligible tendency to gain or lose electrons, which is why Kr is chemically inert under ordinary conditions.
Krypton is recovered as a by-product of fractional distillation of liquefied air. After removing CO2 and H2O, air is liquefied and separated; Kr concentrates in the oxygen–argon fraction and is then further purified.
Yes, under strongly oxidizing conditions krypton forms krypton difluoride, KrF2, a powerful oxidizer and fluorinating agent. It can act as a fluoride donor to strong Lewis acids to give salts such as KrF+ and Kr2F3+ with counteranions like SbF6−. These require low temperatures and anhydrous HF or F2 media.
Lighting: Krypton-filled incandescent and flash lamps reduce filament evaporation and can produce brighter flashes (photography). Lasers: Krypton ion lasers emit visible lines (e.g., red 647 nm, green 531 nm). Excimer lasers: The KrF excimer (transient KrF* molecule) emits near 248 nm, widely used in photolithography and corneal refractive surgery.
Photon energy is given by \(E = h\nu = \dfrac{hc}{\lambda}\). For example, the KrF excimer line at \(\lambda \approx 248\,\text{nm}\) corresponds to higher-energy UV photons than visible krypton-ion lines (e.g., 647 nm).
The orange-red spectral line of \(^{86}\!\mathrm{Kr}\) (wavelength ≈ 605.78 nm) was historically used (1960–1983) as a standard for the meter definition. Modern SI now defines the meter via the speed of light, but Kr’s spectral purity made it useful as a past standard.
Krypton is extremely unreactive, but fluorine is the most electronegative element and can oxidize even noble gases under the right conditions (low temperature, high pressure, or discharge). Formation of Kr–F bonds in KrF2 is driven by the strong stabilization of fluoride and the high oxidizing power of F2.
Krypton-85 is a beta-emitting radionuclide produced in nuclear fission; it is used in leak detection and as a tracer, but it contributes to background radioactivity in the atmosphere. Stable isotopes (e.g., \(^{84}\!\mathrm{Kr}\), \(^{86}\!\mathrm{Kr}\)) are used in lighting and research.
Krypton is non-toxic and inert, but like all inert gases it is an asphyxiation hazard in confined spaces by displacing oxygen. Ensure ventilation, use oxygen monitors in enclosed areas, and follow cylinder handling protocols (upright storage, proper regulators).
Argon is abundant and inexpensive—preferred for general shielding. Krypton offers higher atomic mass and different discharge characteristics, useful for specialty lighting and excimer systems. Xenon provides even brighter lamps and broader excimer chemistry but is rarer and more expensive.