Krypton is the chemical element with symbol Kr and atomic number 36. Like the other noble gases, it is colorless, odorless, flavorless, and non-toxic. Krypton is best-known for producing the bright white of photographic flashes. Here is a collection of interesting krypton facts, including its atomic data, history, uses, and sources.
Krypton Element Facts
Atomic Number: 36
Element Symbol: Kr
Atomic Weight: 83.798(2)
Appearance: Colorless gas
Group: Group 18
Period: Period 4
Element Family: Noble gas
Electron Configuration: [Ar] 3d10 4s2 4p6
Electrons per Shell: 2, 8, 18, 8
Discovery: William Ramsay and Morris Travers (1898)
Name Origin: Greek kryptos: hidden
History of Discovery
William Ramsay and his assistant Morris Travers discovered krypton in 1898 (Britain). They isolated the element from residue remaining after evaporating other components of liquid air. The same method led to the discovery of neon, argon, and xenon. Ramsay named the new element krypton from the Greek word kryptos, which means “hidden.” William Ramsay received the 1904 Nobel Prize in Chemistry for his discovery of noble gases and their place on the periodic table. The only natural noble gas he didn’t discover was radon, but he was the first to isolate it.
Natural krypton consists of five stable isotopes, plus a sixth isotope (78Kr) that has such a long half-life (9.2×1021 years) that it is essentially stable. The most abundant isotope is 84Kr, which accounts for 56.99% of the element. Approximately thirty isomers and instable isotopes exist.
Biological Role and Toxicity
Krypton serves no biological role in any organism. While considered non-toxic, the gas can act as an asphyxiant (similar to helium) and a narcotic. Breathing 50% air with 50% krypton produces narcosis similar to nitrogen narcosis experienced by scuba divers at a depth of 30 m (100 ft).
Sources of Krypton
Krypton is a primordial element. In other words, the element was present when the planet formed and has largely been maintained. The abundance of krypton in the atmosphere is about 1 part per million. Commercially, krypton is obtain by fractional distillation of liquefied air.
Ionized krypton releases bright white light, so krypton finds use in photographic flash bulbs, fluorescent lamps, and “neon” lights. Krypton lasers are used in laser light shows and nuclear fusion research. Electromagnetic calorimeters use liquid krypton. Isotopes find use in magnetic resonance imaging (MRI), computed tomography (CT), and nuclear medicine. Sometimes window panes are insulated with krypton gas between the glass panes. SpaceX uses krypton as a propellent for the Starlink satellites.
Krypton and other noble gases are nearly inert, but they can form compounds under certain conditions. The most important krypton compound is krypton difluoride (KrF2), which is used in a krypton fluoride laser. Krypton hydride (Kr(H2)4) crystals grow under pressures greater than 5 GPa. Polyatomic ions include ArKr+, KrH+, and possibly KrXe+. Unstable compounds include Kr(OTeF5)2 and [HC≡N–Kr–F]+.
Density (at STP): 3.749 g/L
Melting Point: 115.78 K (−157.37 °C, −251.27 °F)
Boiling Point: 119.93 K (−153.415 °C, −244.147 °F)
Triple Point: 115.775 K, 73.53 kPa
Critical Point: 209.48 K, 5.525 MPa
State at 20ºC: gas
Heat of Fusion: 1.64 kJ/mol
Heat of Vaporization: 9.08 kJ/mol
Molar Heat Capacity: 20.95 J/(mol·K)
Thermal Conductivity: 9.43×10−3 W/(m·K)
Crystal Structure: face-centered cubic (fcc)
Magnetic Ordering: diamagnetic
Covalent Radius: 116±4 pm
Van der Waals Radius: 202 pm
Electronegativity: Pauling scale: 3.00
1st Ionization Energy: 1350.8 kJ/mol
2nd Ionization Energy: 2350.4 kJ/mol
3rd Ionization Energy: 3565 kJ/mol
Common Oxidation States: Usually 0, rarely +1 or +2
Fun Krypton Facts
- Solid krypton is white.
- Although ionized krypton appears white, the element has several emission spectrum lines. The strongest lines are yellow and green.
- Because of its low reactivity, krypton escapes from surface water. It lasts much longer in groundwater, so 81Kr can be used to date ground water that is 50,000 to 800,000 years old.
- Detection of the isotope krypton-85 in the atmosphere led to the discovery of North Korean and Pakistani secret nuclear fuel reprocessing facilities.
- Krypton is one of the products from uranium fission.
- Until 1983, the length of the meter was defined based on the wavelength of the krypton-86 orange-red spectral line. (The meter is now defined based on the speed of light.)
- A krypton-fluorine laser can produce a pulse that is more than 500 times more energetic than all of the power of the U.S. electrical grid. However, the pulse is very, very brief (4 billionths of a second).
- Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, FL: CRC Press. ISBN 1439855110.
- Hwang, Shuen-Chen; Lein, Robert D.; Morgan, Daniel A. (2005). “Noble Gases”. Kirk Othmer Encyclopedia of Chemical Technology. Wiley. pp. 343–383. doi:10.1002/0471238961.0701190508230114.a01
- Prusakov, V. N.; Sokolov, V. B. (1971). “Krypton difluoride”. Soviet Atomic Energy. 31 (3): 990–999. doi:10.1007/BF01375764
- Weast, Robert (1984). CRC Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4.