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Krypton
Krypton is a chemical element and a rare noble gas in Group 18 of the periodic table, with the atomic number 36 and symbol "Kr." It is nearly three times heavier than air and is colourless, tasteless, monoatomic, and odourless. Krypton is more abundant in Earth's atmosphere than other places, with traces found in minerals and meteorites. Earth's atmosphere contains approximately 1.14 parts per million of krypton by volume.
1.0Introduction
Krypton was discovered in 1898 by Sir William Ramsay and Morris Travers during the fractional distillation of liquid air. Like other noble gases, krypton’s full outer electron shell makes it resistant to forming compounds with most other elements, contributing to its reputation as an inert gas.
Krypton is found in trace amounts in Earth's atmosphere, making up approximately 1.14 parts per million by volume. It can also be found in minerals and meteorites.
2.0Physical Properties of Krypton
Krypton is a colourless, odourless, tasteless, monoatomic gas about three times heavier than air.
- Atomic number: 36
- Electronic configuration: [Ar] 3d¹⁰ 4s² 4p⁶
- Atomic mass: 83.79 u
- Density: 0.003425 g/cm³
- Melting point: -157.4°C
- Boiling point: -153.4°C
- Nature: Diamagnetic and chemically inert due to its fully filled valence shell.
In its solid state, krypton forms a face-centred cubic crystalline structure, similar to other noble gases. At high temperatures, krypton behaves similarly to neon but emits a purple glow instead of red. When mixed with other gases, krypton produces a greenish-yellow light.
Interestingly, krypton is more concentrated at the North Pole than at the South Pole due to convective mixing, a process where solid particles disperse within one another.
Although krypton is rare on Earth, it is relatively common in stars, including the sun.
3.0Chemical Properties of Krypton
- Krypton typically exhibits oxidation states of 0 and +2, with the +2 oxidation state being observed in certain compounds with fluorine.
- Due to its full outermost electron shell, krypton is highly unreactive, and its oxidation state generally remains zero.
- Krypton isotopes range in mass from 69 to 102. A total of 34 isotopes have been identified and studied, including five stable isotopes and one radioactive isotope with a long half-life.
- The stable isotopes found in nature include 78Kr, 80Kr, 82Kr, 83Kr, 84Kr, and 86Kr.
- Although krypton is inert mainly, it emits intense spectral lines, primarily in the green and yellow regions of the spectrum.
- Krypton is sparingly soluble in water at temperatures between 30°C and 40°C.
Although traditionally considered unreactive, krypton can form compounds with highly electronegative elements, such as fluorine, under specific conditions. In its +2 oxidation state, krypton reacts with fluorine at extremely low temperatures (-196°C) in the presence of an electrical discharge to form krypton difluoride (KrF2). This compound is unstable and decomposes at higher temperatures. Importantly, krypton reacts exclusively with fluorine and does not form compounds with other halogens.
4.0Uses of Krypton
- Lighting: Krypton is widely used in various lights, including small bright flashlight bulbs and unique strobe lights for airport runways.
- Photography and Film: Due to krypton's numerous spectral lines, its ionised gas emits white light, making it ideal for photography and studio lighting in the film industry.
- Neon Lights: Krypton reacts with other gases in neon lights to produce a bright yellow glow.
- Glow-in-the-Dark Materials: The isotope 85Kr, in combination with phosphors, is used to create glow-in-the-dark materials, as it reflects off phosphors.
- Lasers: Krypton is used in lasers, especially for producing red light in laser light shows, due to its higher light density in the red spectral region than other gases like neon.
- Krypton-Fluoride Laser: One of krypton’s most important applications is in krypton-fluoride lasers used in nuclear fusion energy research.