Krypton (from Ancient Greek: κρυπτός, translit. kryptos "the hidden one") is a chemical element with symbol Kr and atomic number 36. It is a member of group 18 (noble gases) elements. A colorless, odorless, tasteless noble gas, krypton occurs in trace amounts in the atmosphere and is often used with other rare gases in fluorescent lamps. With rare exceptions, krypton is chemically inert.

Krypton, like the other noble gases, is used in lighting and photography. Krypton light has many spectral lines, and krypton plasma is useful in bright, high-powered gas lasers (krypton ion and excimer lasers), each of which resonates and amplifies a single spectral line. Krypton fluoride also makes a useful laser medium. From 1960 to 1983, the official length of a meter was defined by the 605 nm wavelength of the orange spectral line of krypton-86, because of the high power and relative ease of operation of krypton discharge tubes.

Krypton,  36Kr
Krypton discharge tube
A krypton-filled discharge tube glowing white
Pronunciation/ˈkrɪptɒn/ (KRIP-ton)
Appearancecolorless gas, exhibiting a whitish glow in an electric field
Standard atomic weight Ar, std(Kr)83.798(2)[1]
Krypton in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson


Atomic number (Z)36
Groupgroup 18 (noble gases)
Periodperiod 4
Element category  noble gas
Electron configuration[Ar] 3d10 4s2 4p6
Electrons per shell
2, 8, 18, 8
Physical properties
Phase at STPgas
Melting point115.78 K ​(−157.37 °C, ​−251.27 °F)
Boiling point119.93 K ​(−153.415 °C, ​−244.147 °F)
Density (at STP)3.749 g/L
when liquid (at b.p.)2.413 g/cm3[2]
Triple point115.775 K, ​73.53 kPa[3][4]
Critical point209.48 K, 5.525 MPa[4]
Heat of fusion1.64 kJ/mol
Heat of vaporization9.08 kJ/mol
Molar heat capacity20.95[5] J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 59 65 74 84 99 120
Atomic properties
Oxidation states0, +1, +2 (rarely more than 0; oxide is unknown)
ElectronegativityPauling scale: 3.00
Ionization energies
  • 1st: 1350.8 kJ/mol
  • 2nd: 2350.4 kJ/mol
  • 3rd: 3565 kJ/mol
Covalent radius116±4 pm
Van der Waals radius202 pm
Color lines in a spectral range
Spectral lines of krypton
Other properties
Natural occurrenceprimordial
Crystal structureface-centered cubic (fcc)
Face-centered cubic crystal structure for krypton
Speed of sound(gas, 23 °C) 220 m·s−1
(liquid) 1120 m/s
Thermal conductivity9.43×10−3  W/(m·K)
Magnetic orderingdiamagnetic[6]
Magnetic susceptibility−28.8·10−6 cm3/mol (298 K)[7]
CAS Number7439-90-9
Discovery and first isolationWilliam Ramsay and Morris Travers (1898)
Main isotopes of krypton
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
78Kr 0.36% 9.2×1021 y[8] εε 78Se
79Kr syn 35 h ε 79Br
β+ 79Br
80Kr 2.29% stable
81Kr trace 2.3×105 y ε 81Br
82Kr 11.59% stable
83Kr 11.50% stable
84Kr 56.99% stable
85Kr syn 11 y β 85Rb
86Kr 17.28% stable


William Ramsay working
Sir William Ramsay, the discoverer of krypton

Krypton was discovered in Britain in 1898 by Sir William Ramsay, a Scottish chemist, and Morris Travers, an English chemist, in residue left from evaporating nearly all components of liquid air. Neon was discovered by a similar procedure by the same workers just a few weeks later.[9] William Ramsay was awarded the 1904 Nobel Prize in Chemistry for discovery of a series of noble gases, including krypton.

In 1960, the International Conference on Weights and Measures defined the meter as 1,650,763.73 wavelengths of light emitted by the krypton-86 isotope.[10][11] This agreement replaced the 1889 international prototype meter located in Paris, which was a metal bar made of a platinum-iridium alloy (one of a series of standard meter bars, originally constructed to be one ten-millionth of a quadrant of the Earth's polar circumference). This also obsoleted the 1927 definition of the ångström based on the red cadmium spectral line,[12] replacing it with 1 Å = 10−10 m. The krypton-86 definition lasted until the October 1983 conference, which redefined the meter as the distance that light travels in vacuum during 1/299,792,458 s.[13][14][15]


Krypton is characterized by several sharp emission lines (spectral signatures) the strongest being green and yellow.[16] Krypton is one of the products of uranium fission.[17] Solid krypton is white and has a face-centered cubic crystal structure, which is a common property of all noble gases (except helium, which has a hexagonal close-packed crystal structure).


Naturally occurring krypton in Earth's atmosphere is composed of five stable isotopes, plus one isotope (78Kr) with such a long half-life (9.2×1021 years) that it can be considered stable. (This isotope has the second-longest known half-life among all isotopes for which decay has been observed; it undergoes double electron capture to 78Se).[8][18] In addition, about thirty unstable isotopes and isomers are known.[19] Traces of 81Kr, a cosmogenic nuclide produced by the cosmic ray irradiation of 80Kr, also occur in nature: this isotope is radioactive with a half-life of 230,000 years. Krypton is highly volatile and does not stay in solution in near-surface water, but 81Kr has been used for dating old (50,000–800,000 years) groundwater.[20]

85Kr is an inert radioactive noble gas with a half-life of 10.76 years. It is produced by the fission of uranium and plutonium, such as in nuclear bomb testing and nuclear reactors. 85Kr is released during the reprocessing of fuel rods from nuclear reactors. Concentrations at the North Pole are 30% higher than at the South Pole due to convective mixing.[21]


Krypton hydride crystal
Kr(H2)4 and H2 solids formed in a diamond anvil cell.[22]
Krypton hydride structure
Structure of Kr(H2)4. Krypton octahedra (green) are surrounded by randomly oriented hydrogen molecules.[22]

Like the other noble gases, krypton is highly chemically unreactive. The rather restricted chemistry of krypton in its only known nonzero oxidation state of +2 parallels that of the neighboring element bromine in the +1 oxidation state; due to the scandide contraction it is difficult to oxidize the 4p elements to their group oxidation states. Before the 1960s, no noble gas compounds had been synthesized.[23]

However, following the first successful synthesis of xenon compounds in 1962, synthesis of krypton difluoride (KrF
) was reported in 1963. In the same year, KrF
was reported by Grosse, et al.,[24] but was subsequently shown to be a mistaken identification.[25] Under extreme conditions, krypton reacts with fluorine to form KrF2 according to the following equation:

Kr + F2 → KrF2

Compounds with krypton bonded to atoms other than fluorine have also been discovered. There are also unverified reports of a barium salt of a krypton oxoacid.[26] ArKr+ and KrH+ polyatomic ions have been investigated and there is evidence for KrXe or KrXe+.[27]

The reaction of KrF
with B(OTeF
produces an unstable compound, Kr(OTeF
, that contains a krypton-oxygen bond. A krypton-nitrogen bond is found in the cation [HC≡N–Kr–F]+
, produced by the reaction of KrF
with [HC≡NH]+
] below −50 °C.[28][29] HKrCN and HKrC≡CH (krypton hydride-cyanide and hydrokryptoacetylene) were reported to be stable up to 40 K.[23]

Krypton hydride (Kr(H2)4) crystals can be grown at pressures above 5 GPa. They have a face-centered cubic structure where krypton octahedra are surrounded by randomly oriented hydrogen molecules.[22]

Natural occurrence

Earth has retained all of the noble gases that were present at its formation except helium. Krypton's concentration in the atmosphere is about 1 ppm. It can be extracted from liquid air by fractional distillation.[30] The amount of krypton in space is uncertain, because measurement is derived from meteoric activity and solar winds. The first measurements suggest an abundance of krypton in space.[31]


Krypton gas discharge tube

Krypton's multiple emission lines make ionized krypton gas discharges appear whitish, which in turn makes krypton-based bulbs useful in photography as a brilliant white light source. Krypton is used in some photographic flashes for high speed photography. Krypton gas is also combined with other gases to make luminous signs that glow with a bright greenish-yellow light.[32]

Krypton is mixed with argon in energy efficient fluorescent lamps, reducing the power consumption, but also reducing the light output and raising the cost.[33] Krypton costs about 100 times as much as argon. Krypton (along with xenon) is also used to fill incandescent lamps to reduce filament evaporation and allow higher operating temperatures.[34] A brighter light results with more blue color than conventional incandescent lamps.

Krypton's white discharge is often used to good effect in colored gas discharge tubes, which are simply painted or stained to create the desired color (for example, "neon" type multi-colored advertising signs are often entirely krypton-based). Krypton produces much higher light power than neon in the red spectral line region, and for this reason, red lasers for high-power laser light-shows are often krypton lasers with mirrors that select the red spectral line for laser amplification and emission, rather than the more familiar helium-neon variety, which could not achieve the same multi-watt outputs.[35]

The krypton fluoride laser is important in nuclear fusion energy research in confinement experiments. The laser has high beam uniformity, short wavelength, and the spot size can be varied to track an imploding pellet.[36]

In experimental particle physics, liquid krypton is used to construct quasi-homogeneous electromagnetic calorimeters. A notable example is the calorimeter of the NA48 experiment at CERN containing about 27 tonnes of liquid krypton. This usage is rare, since liquid argon is less expensive. The advantage of krypton is a smaller Molière radius of 4.7 cm, which provides excellent spatial resolution with little overlapping. The other parameters relevant for calorimetry are: radiation length of X0=4.7 cm, and density of 2.4 g/cm3.

The sealed spark gap assemblies in ignition exciters in some older jet engines contain a small amount of krypton-85 to produce consistent ionization levels and uniform operation.

Krypton-83 has application in magnetic resonance imaging (MRI) for imaging airways. In particular, it enables the radiologist to distinguish between hydrophobic and hydrophilic surfaces containing an airway.[37]

Although xenon has potential for use in computed tomography (CT) to assess regional ventilation, its anesthetic properties limit its fraction in the breathing gas to 35%. A breathing mixture of 30% xenon and 30% krypton is comparable in effectiveness for CT to a 40% xenon fraction, while avoiding the unwanted effects of a high partial pressure of xenon gas.[38]

The metastable isotope krypton-81m is used in nuclear medicine for lung ventilation/perfusion scans, where it is inhaled and imaged with a gamma camera.[39]

Krypton-85 in the atmosphere has been used to detect clandestine nuclear fuel reprocessing facilities in North Korea[40] and Pakistan.[41] Those facilities were detected in the early 2000s and were believed to be producing weapons-grade plutonium.

Krypton is used occasionally as an insulating gas between window panes.[42]


Krypton is considered to be a non-toxic asphyxiant.[43] Krypton has a narcotic potency seven times greater than air, and breathing an atmosphere of 50% krypton and 50% natural air (as might happen in the locality of a leak) causes narcosis in humans similar to breathing air at four times atmospheric pressure. This is comparable to scuba diving at a depth of 30 m (100 ft) (see nitrogen narcosis) and could affect anyone breathing it. At the same time, that mixture would contain only 10% oxygen (rather than the normal 20%) and hypoxia would be a greater concern.


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Further reading

External links

Argo City

Argo City is a fictional extraterrestrial city appearing in American comic books published by DC Comics. Located on the planet Krypton, it is the birthplace of Supergirl. Argo City first appeared in Action Comics #252 (May 1959).

BlackBerry Motion

The BlackBerry Motion is an Android smartphone manufactured by TCL Corporation under the brand name of BlackBerry Mobile. It was launched on 9 October 2017 in Dubai at the Gitex Technology Week, and first went on sale in the United Arab Emirates and Saudi Arabia on 22 October 2017.

Eradicator (comics)

The Eradicator is the given name of four different fictional comic book characters, appearing in books published by DC Comics. The first iteration was an antihero character appearing in the Flash series of comics. The second was a superhero (and sometimes supervillain) having a recurring role in Superman stories, and the remaining two first appeared in 2013 and 2017, respectively.

The Flash Eradicator was created by Carmine Infantino and Cary Bates and first appeared in The Flash #314. The first Superman character was created by writer Roger Stern and artist Curt Swan, and first appeared in Action Comics Annual #2 (1989).

H'El on Earth

"H'El on Earth" is a Superman crossover story arc published by DC Comics. Written primarily by Scott Lobdell, it details the appearance of H'El, a mysterious Kryptonian.

Ion laser

An ion laser is a gas laser that uses an ionized gas as its lasing medium.

Like other gas lasers, ion lasers feature a sealed cavity containing the laser medium and mirrors forming a Fabry–Pérot resonator. Unlike helium–neon lasers, the energy level transitions that contribute to laser action come from ions. Because of the large amount of energy required to excite the ionic transitions used in ion lasers, the required current is much greater, and as a result all but the smallest ion lasers are water-cooled. A small air-cooled ion laser might produce, for example, 130 milliwatts of output light with a tube current of about 10 amperes and a voltage of 105 volts. Since one ampere times one volt is one watt, this is an electrical power input of about one kilowatt. Subtracting the (desirable) light output of 130 mW from power input, this leaves the large amount of waste heat of nearly one kW. This has to be dissipated by the cooling system. In other words, the power efficiency is very low.

Isotopes of krypton

There are 33 known isotopes of krypton (36Kr) with atomic mass numbers from 69 through 101. Naturally occurring krypton is made of five stable isotopes and one (78Kr) which is slightly radioactive with an extremely long half-life, plus traces of radioisotopes that are produced by cosmic rays in the atmosphere.


Jor-El, originally known as Jor-L, is a fictional character appearing in comic books published by DC Comics. Created by writer Jerry Siegel and artist Joe Shuster, Jor-El first appeared in a newspaper comic strip in 1939 with Superman.

A Kryptonian, Jor-El is Superman's biological father, the husband of Lara, and a leading scientist on the planet Krypton before its destruction. He foresaw the planet's fate but was unable to convince his colleagues in time to save the inhabitants. Jor-El was able to save his infant son Kal-El (Superman) by sending him in a homemade spaceship towards Earth just moments before Krypton exploded. After constructing his Fortress of Solitude, Superman honored his biological parents with a statue of Jor-El and Lara holding up a globe of Krypton.

Kandor (comics)

Kandor () is a fictional city appearing in American comic books published by DC Comics.

Kandor is the former capital city of the planet Krypton and is best known for being miniaturized and then stolen by the supervillain Brainiac. Upon its recovery by Superman, it has been kept and monitored in the Fortress of Solitude.

Krypton (TV series)

Krypton is an American television series developed by David S. Goyer for Syfy. The series takes place on the eponymous fictional planet, approximately 200 years before the birth of Kal-El / Superman and eventual destruction of the planet, focusing on his grandfather, Seg-El (Cameron Cuffe). Krypton premiered on March 21, 2018. Its first season consists of ten episodes. In May 2018, Syfy renewed Krypton for a second season, which is expected to premiere in 2019.

Krypton (comics)

Krypton is a fictional planet appearing in American comic books published by DC Comics. The planet is the native world of Superman and is named after the element krypton. The planet was created by Jerry Siegel and Joe Shuster, and was first referred to in Action Comics #1 (June 1938). The planet made its first full appearance in Superman #1 (summer 1939).

Krypton is also the native world of Supergirl, Krypto the Superdog, and Power Girl (in her case, an alternate-universe version designated "Krypton-Two"). It has been consistently described as having been destroyed shortly after Superman's flight from the planet, although the exact details of its destruction vary by time period and writers. Kryptonians were the dominant species on Krypton.

Krypton difluoride

Krypton difluoride, KrF2 is a chemical compound of krypton and fluorine. It was the first compound of krypton discovered. It is a volatile, colourless solid. The structure of the KrF2 molecule is linear, with Kr−F distances of 188.9 pm. It reacts with strong Lewis acids to form salts of the KrF+ and Kr2F+3 cations.The atomization energy of KrF2 (KrF2(g) → Kr(g) + 2F(g)) is 21.9 kcal/mol, giving an average Kr–F bond energy of only 11 kcal/mol, the weakest of any isolable fluoride. In comparison, difluorine is held together by a bond of 36 kcal/mol. Consequently, KrF2 is a good source of the extremely reactive and oxidizing atomic fluorine. It is thermally unstable, with a decomposition rate of 10% per hour at room temperature. Krypton difluoride is endothermic, with a heat of formation of 14.4 ± 0.8 kcal/mol measured at 93 °C.


Kryptonians are a fictional extraterrestrial race of humanoids within the DC Comics universe that originated on the planet Krypton. The term originated from the stories of DC Comics superhero, Superman. The stories also use "Kryptonian" as an adjective to refer to anything created by or associated with the planet itself or the cultures that existed on it.

Members of the dominant species of the planet Krypton are indistinguishable from humans in terms of their appearance; their physiology and genetics; however, they are vastly different. In some continuities Kryptonians are difficult to clone because their DNA is so complex that human science is not advanced enough to decipher it. The cellular structure of Kryptonians allows for solar energy to be absorbed at extremely high levels. On the planet Krypton, whose parent star has often been depicted as an ancient red supergiant with a relatively low energy output, their natural abilities were the same as humans. When exposed to a young yellow star like Earth's Sun, which is much smaller than their own sun and with a vastly higher energy output, their bodies are able to absorb and process so much energy that it eventually manifests as vast superhuman powers (such as superhuman strength, superhuman speed, invulnerability, flight, x-ray vision, heat vision and superhuman senses).

Almost all Kryptonians were killed when the planet exploded shortly after the infant Kal-El was sent to Earth. In some continuities, he is the planet's only survivor.


Kryptonopolis is a fictional city in the DC Comics universe. Located on the planet Krypton, it is the birthplace of Superman.

Noble gas

The noble gases (historically also the inert gases; sometimes referred to as aerogens) make up a group of chemical elements with similar properties; under standard conditions, they are all odorless, colorless, monatomic gases with very low chemical reactivity. The six noble gases that occur naturally are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and the radioactive radon (Rn). These elements are all nonmetals. Oganesson (Og) is variously predicted to be a noble gas as well or to break the trend due to relativistic effects; its chemistry has not yet been investigated.

For the first six periods of the periodic table, the noble gases are exactly the members of group 18. Noble gases are typically highly unreactive except when under particular extreme conditions. The inertness of noble gases makes them very suitable in applications where reactions are not wanted. For example, argon is used in incandescent lamps to prevent the hot tungsten filament from oxidizing; also, helium is used in breathing gas by deep-sea divers to prevent oxygen, nitrogen and carbon dioxide (hypercapnia) toxicity.

The properties of the noble gases can be well explained by modern theories of atomic structure: their outer shell of valence electrons is considered to be "full", giving them little tendency to participate in chemical reactions, and it has been possible to prepare only a few hundred noble gas compounds. The melting and boiling points for a given noble gas are close together, differing by less than 10 °C (18 °F); that is, they are liquids over only a small temperature range.

Neon, argon, krypton, and xenon are obtained from air in an air separation unit using the methods of liquefaction of gases and fractional distillation. Helium is sourced from natural gas fields that have high concentrations of helium in the natural gas, using cryogenic gas separation techniques, and radon is usually isolated from the radioactive decay of dissolved radium, thorium, or uranium compounds (since those compounds give off alpha particles). Noble gases have several important applications in industries such as lighting, welding, and space exploration. A helium-oxygen breathing gas is often used by deep-sea divers at depths of seawater over 55 m (180 ft) to keep the diver from experiencing oxygen toxemia, the lethal effect of high-pressure oxygen, nitrogen narcosis, the distracting narcotic effect of the nitrogen in air beyond this partial-pressure threshold, and carbon dioxide poisoning (hypercapnia), the panic-inducing effect of excessive carbon dioxide in the bloodstream. After the risks caused by the flammability of hydrogen became apparent, it was replaced with helium in blimps and balloons.

Origin of Superman

The origin of Superman is the story that relates Superman's arrival on Earth and the beginnings of his career as a superhero. The story has been through many revisions through decades of publication in comic books and radio, television and film adaptations.

The original story was written by Jerry Siegel and illustrated by Joe Shuster, and published as a part of the character's first appearance in Action Comics #1 (June 1938). As more stories were published, more details about the original story were established. These stories explored individual details, such as the planet Krypton, the source of Superman's powers and his relationships with supporting characters. Because continuity was looser during the Golden Age and the Silver Age, many of these stories contradicted each other.

As Superman was adapted into other media, his origin story has been frequently retold. These origin stories adhere to the basic framework created by Siegel and Shuster, with minor variations made to serve the plot or to appeal to contemporary audiences. Some of the details created for these adaptations influenced the origin story in the mainstream comic series.

In more recent years, the origin story has been revamped in the comic books several times. In 1985, DC Comics published Crisis on Infinite Earths, which created the opportunity to definitively revise the history of the DC Universe. Superman's origin was subsequently retold in the 1986 limited series The Man of Steel, written and drawn by John Byrne. The story was later removed from continuity ("retconned") and replaced with the Superman: Birthright limited series in 2003 and 2004, written by Mark Waid and drawn by Leinil Francis Yu, as Superman's official origin. After the Infinite Crisis limited series in 2005 and 2006, Superman's origin was revised yet again, unfolding throughout Superman's regular publications and the Superman: Secret Origin mini-series in 2009 and 2010.


Seyg-El is a fictional character appearing in American comic books published by DC Comics. He is Superman and Supergirl's grandfather and the father of Jor-El and Zor-El. He is the former head of the Kryptonian Council. He appeares in the live action television series Krypton, portrayed by Cameron Cuffe.

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