Krypton

Krypton. It is a chemical element with the symbol Kr and atomic number 36, classified as a noble gas in group 18 of the periodic table. Discovered in 1898 by William Ramsay and Morris Travers through the fractional distillation of liquid air, it is a colorless, odorless, and tasteless gas that is present in trace amounts in the Earth's atmosphere. While generally inert, it forms a limited number of chemical compounds and has several specialized applications, notably in lighting and laser technology.

Properties

Krypton is a member of the noble gas family, characterized by its filled electron shell configuration which confers high chemical stability. At standard temperature and pressure, it exists as a monatomic gas with a density approximately three times that of air. It exhibits a brilliant whitish glow, often with spectral lines in the visible spectrum, when electrically excited, a property utilized in certain gas-discharge lamps. The element has a relatively narrow liquid range between its melting point and boiling point, and it can form a solid with a face-centered cubic crystal structure under sufficient cooling.

History

The element was discovered on May 30, 1898, by the Scottish chemist William Ramsay and his English assistant Morris Travers at University College London. They isolated it from the residue left after evaporating nearly all components of liquid air, following their earlier discoveries of argon and helium. The name derives from the Ancient Greek word *kryptos*, meaning "hidden," reflecting its elusive nature in the atmosphere. Its spectral signature was later confirmed by the German physicists Heinrich Hertz and Gustav Kirchhoff, and its place among the noble gases was solidified by the work of Lord Rayleigh.

Occurrence and production

Krypton is found in trace quantities in the Earth's atmosphere, at a concentration of about 1 part per million by volume. It is also present in some natural gas wells and is produced as a byproduct of the nuclear fission of uranium and plutonium in nuclear reactors. Commercially, it is obtained through the fractional distillation of liquefied air in large air separation plants, a process that also yields nitrogen, oxygen, argon, neon, and xenon. The global production is limited, making it one of the more expensive atmospheric gases.

Compounds

Due to its status as a noble gas, krypton was long considered completely inert, but the first compound, krypton difluoride (KrF₂), was synthesized in 1963 by the American chemist Neil Bartlett. This discovery followed his groundbreaking work with xenon hexafluoroplatinate. Other known compounds include krypton tetrafluoride (KrF₄) and various unstable clathrates and exciplexes formed under extreme conditions. Research into krypton chemistry is primarily of academic interest, exploring the boundaries of chemical bonding and the reactivity of heavy noble gases.

Applications

A primary use of krypton is in energy-efficient lighting, where it fills certain types of incandescent lamps and fluorescent lamps to reduce filament evaporation and improve efficiency. It is a key component in high-performance gas-discharge lamps, such as those used in photography and projection systems, due to its bright white light. The krypton fluoride laser (KrF laser) is an important excimer laser used in semiconductor manufacturing for photolithography. The isotope krypton-85 is used in HID lamps and as a tracer in environmental science, while liquid krypton serves as a target in particle physics experiments like those at CERN.

Isotopes

Naturally occurring krypton is composed of six stable isotopes: ⁷⁸Kr, ⁸⁰Kr, ⁸²Kr, ⁸³Kr, ⁸⁴Kr, and ⁸⁶Kr, with ⁸⁴Kr being the most abundant. Several radioactive isotopes are known, with ⁸¹Kr (half-life 230,000 years) used in radiometric dating of ancient groundwater and polar ice. The fission product ⁸⁵Kr (half-life 10.76 years) is a beta emitter monitored for nuclear non-proliferation and atmospheric tracing. The synthetic isotopes. The isotope. The International Union of Pure and Applied Chemistry maintains the standard atomic weights for these isotopes.