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Krypton at Chemical Elements.com

Basic Information | Atomic Structure | Isotopes | Related Links | Citing This Page

Basic Information

Name: Krypton

Symbol: Kr

Atomic Number: 36

Atomic Mass: 83.8 amu

Melting Point: -157.2 °C (115.950005 K, -250.95999 °F)

Boiling Point: -153.4 °C (119.75001 K, -244.12 °F)

Number of Protons/Electrons: 36

Number of Neutrons: 48

Classification: Noble Gas

Crystal Structure: Cubic

Density @ 293 K: 3.74 g/cm3

Color: colorless gas

Atomic Structure

[Bohr Model of Krypton] 

Number of Energy Levels: 4

    First Energy Level: 2

    Second Energy Level: 8

    Third Energy Level: 18

    Fourth Energy Level: 8


IsotopeHalf Life
Kr-791.45 days
Kr-81210000.0 years
Kr-83m1.86 hours
Kr-8510.73 years
Kr-85m4.48 hours
Kr-871.27 hours
Kr-882.84 hours
Kr-893.15 minutes
Kr-9032.3 seconds


Date of Discovery: 1898

Discoverer: Sir William Ramsay

Name Origin: From the Greek word kryptos (hidden)

Uses: Lighting

Obtained From: production of liquid air

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chemical element
Written By:

  • Gary J. Schrobilgen
See Article History

Alternative Title:

Krypton (Kr), chemical element , rare gas of Group 18 ( noble gases ) of the periodic table , which forms relatively few chemical compounds . About three times heavier than air , krypton is colourless, odourless, tasteless, and monatomic. Although traces are present in meteorites and minerals , krypton is more plentiful in Earth’s atmosphere , which contains 1.14 parts per million by volume of krypton. The element was discovered in 1898 by the British chemists Sir William Ramsay and Morris W. Travers in the residue left after a sample of liquid air had boiled almost entirely away.

Element Properties
atomic number36
atomic weight83.80
melting point−156.6 °C (−249.9 °F)
boiling point−152.3 °C (−242.1 °F)
density (1 atm, 0 °C [32 °F])3.733 g/litre (0.049 ounce/gallon)
oxidation numbers 0, 2
electron config.(Ar)3d104s24p6
Read More on This Topic

Apparatus used in the isolation of argon by English physicist Lord Rayleigh and chemist Sir William Ramsay, 1894Air is contained in a test tube (A) standing over a large quantity of weak alkali (B), and an electric spark is sent across wires (D) insulated by U-shaped glass tubes (C) passing through the liquid and around the mouth of the test tube. The spark oxidizes the nitrogen in the air, and the oxides of nitrogen are then absorbed by the alkali. After oxygen is removed, what remains in the test tube is argon.

noble gas

(Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn), and oganesson (Og). The noble gases are colourless, odourless, tasteless, nonflammable gases. They traditionally have been labeled Group 0 in the periodic table because for decades after their discovery it was believed that

Properties of the element

Because its boiling point (−152.3 °C, or −242.1 °F) is about 30–40 °C (50–70 °F) higher than those of the major constituents of air, krypton is readily separated from liquid air by fractional distillation; it accumulates along with xenon in the least volatile portion. These two gases are further purified by adsorption onto silica gel , redistillation, and passage over hot titanium metal , which removes all impurities except other noble gases.

Krypton is used in certain electric and fluorescent lamps and in a flashlamp employed in high-speed photography . Radioactive krypton-85 is useful for detecting leaks in sealed containers, with the escaping atoms detected by means of their radiation . Krypton is named from the Greek word kryptos, “hidden.”

When a current of electricity is passed through a glass tube containing krypton at low pressure , a bluish white light is emitted. The wavelength of an orange-red component of light emitted by stable krypton-86, because of its extreme sharpness, served from 1960 to 1983 as the international standard for the metre . (One metre equaled 1,650,763.73 times the wavelength of this line.)

Natural krypton is a mixture of six stable isotopes : krypton-84 (57.0 percent), krypton-86 (17.3 percent), krypton-82 (11.6 percent), krypton-83 (11.5 percent), krypton-80 (2.25 percent), and krypton-78 (0.35 percent). Krypton has isotopes of every mass number from 69 through 100; of these isotopes; twenty-five are radioactive and are produced by fission of uranium and by other nuclear reactions . The longest lived of these, krypton-81, has a half-life of 229,000 years. After it has been stored a few days, krypton obtained by nuclear fission contains only one radioactive isotope , krypton-85, which has a half-life of 10.8 years, because all the other radioactive isotopes have half-lives of 3 hours or less.


Krypton is the lightest of the noble gases that form isolable chemical compounds in macroscopic amounts. For many years it was considered to be totally unreactive. In the early 1960s, however, krypton was found to react with the element fluorine when both are combined in an electrical-discharge tube at −183 °C (−297 °F); the compound formed is krypton difluoride, KrF2. Several other methods for the synthesis of KrF2 are now known, including irradiation of krypton and fluorine mixtures with ultraviolet radiation at −196 °C (−321 °F).

KrF2 is a colourless crystalline solid that is highly volatile and slowly decomposes at room temperature. No other molecular fluoride of krypton has been isolated, so all krypton compounds are derived from KrF2, where Kr is in the +2 oxidation state . Krypton difluoride is a powerful oxidative fluorinating agent. (Its oxidizing power means that it extracts electrons from other substances and confers on them a positive charge. Its fluorinating ability means that it transfers an F ion to other substances. Hence, in a formal sense, oxidative fluorination is the net result of extraction of two electrons and addition of F; this can be considered to be equivalent to the transfer of F+.) KrF2 is, for example, capable of oxidizing and fluorinating xenon to XeF6 and gold to AuF5.

The cationic species KrF+ and Kr2F3+ are formed in reactions of KrF2 with strong fluoride-ion acceptors such as the pentafluorides of Group 15, in which the fluoride ion F is transferred to the pentafluoride to give complex salts that are analogous to those of XeF2; here no oxidation is involved. Among these complex salts are [KrF+][SbF6] and [Kr2F3+][AsF6]. The Kr2F3+ cation is V-shaped with a fluorine atom bonded to each of two krypton atoms and both krypton atoms bonded to a common fluorine in the middle, i.e., F(KrF)2+.

The KrF+ cation ranks among the most powerful chemical oxidizers presently known and is capable of oxidative fluorination of gaseous xenon to XeF5+ and chlorine , bromine , and iodine pentafluorides to the ClF6+, BrF6+, and IF6+ cations, respectively. The KrF+ cation behaves as only an oxidizing agent in converting gaseous oxygen to O2+.

The KrF+ cation has been shown to behave as a Lewis acid ( electron -pair acceptor) toward a number of Lewis bases that are resistant to oxidation by the strongly oxidizing KrF+ cation at low temperatures. These Lewis acid-base adducts are exemplified by HCNKrF+ and F3CCNKrF+, which are formed as AsF6 salts. Such cations are the only known examples of krypton bonded to nitrogen . The compound Kr(OTeF5)2 is the only reported example of a compound in which krypton is bonded to oxygen. No compounds in which krypton is bonded to elements other than fluorine, oxygen, and nitrogen have been isolated.

Clathrate “compounds,” in which the element is trapped in cagelike structures of water or other molecules, are known. There is no diatomic molecule of krypton.

Gary J. Schrobilgen

Learn More in these related Britannica articles:

  • Apparatus used in the isolation of argon by English physicist Lord Rayleigh and chemist Sir William Ramsay, 1894Air is contained in a test tube (A) standing over a large quantity of weak alkali (B), and an electric spark is sent across wires (D) insulated by U-shaped glass tubes (C) passing through the liquid and around the mouth of the test tube. The spark oxidizes the nitrogen in the air, and the oxides of nitrogen are then absorbed by the alkali. After oxygen is removed, what remains in the test tube is argon.

    noble gas
    (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn), and oganesson (Og). The noble gases are colourless, odourless, tasteless, nonflammable gases. They traditionally have been labeled Group 0 in the periodic table because for decades after their discovery it was believed that…
  • crystal bonding

    chemical bonding: Potassium through krypton
    …to the next noble gas, krypton. The presence of the 3d orbitals in the scheme of occupation lengthens the fourth row of the periodic table from 8 to 18 members, and the row from potassium to krypton is called the first long period of the periodic table.…
  • The Balmer series of hydrogen as seen by a low-resolution spectrometer.

    spectroscopy: RIS schemes
    For example, the inert element krypton has an ionization potential of 14.0 electron volts and requires a more elaborate RIS scheme of the type shown in Figure 14B. The first step is a resonance transition at the wavelength of 116.5 nanometres, followed by a second resonance step at 558.1 nanometres.…
  • Figure 1: Unit cells for face-centred and body-centred cubic lattices.

    crystal: Structures of metals
    solids neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe). Their melting temperatures at atmospheric pressure are: Ne, 24.6 K; Ar, 83.8 K; Kr, 115.8 K; and Xe, 161.4 K.…
  • The atmospheres of planets in the solar system are composed of various gases, particulates, and liquids. They are also dynamic places that redistribute heat and other forms of energy. On Earth, the atmosphere provides critical ingredients for living things. Here, feathery cirrus clouds drift across deep blue sky over Colorado's San Miguel Mountains.

    …neon (Ne), helium (He), and krypton (Kr) and other constituents such as nitrogen oxides, compounds of sulfur, and compounds of ozone are found in lesser amounts.…


  • First ionization energies of the elements.

More About Krypton

7 references found in Britannica articles

Assorted References

    • major reference
      • In noble gas
    • Earth atmosphere
      • In atmosphere
    • lasers
      • In laser: Types of lasers
    • work of Ramsay
      • In Sir William Ramsay: Discovery of noble gases

    properties and structure

      • Aufbau principle
        • In chemical bonding: Potassium through krypton
      • crystal structure
        • In crystal: Structures of metals
      • resonance ionization
        • In spectroscopy: RIS schemes

      Additional Reading

      External Websites

      • Los Alamos National Laboratory – Krypton
      • WebElements – Krypton
      • Chemicool – Krypton
      • Rader’s Chem4Kids.com – Krypton
      • Royal Society of Chemistry – Krypton
      Britannica Websites
      Articles from Britannica Encyclopedias for elementary and high school students.
      • krypton – Student Encyclopedia (Ages 11 and up)

      Article History

      Article Contributors


      Corrections? Updates? Help us improve this article!
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