Kr 36

Krypton (Kr)

noble-gas

Period: 4 Group: 18 Block: p

Gas

Standard Atomic Weight

Electron configuration

[Ar] 4s² 3d¹⁰ 4p⁶

Melting point

-157.36 °C (115.79 K)

Boiling point

-153.42 °C (119.73 K)

Density

3.733 kg/m³

Oxidation states

0, +1, +2

Electronegativity (Pauling)

Ionization energy (1st)

Discovery year

1898

Atomic radius

N/A

Details

Name origin Greek: kryptos (hidden).

Discovery country Great Britain

Discoverers Sir William Ramsey, M.W. Travers

Krypton is a heavy noble gas in group 18. It is chemically very inert under ordinary conditions, monatomic, colorless, and present in air only as a minor trace constituent. Its closed electron shell makes compound formation difficult, but not impossible under strongly oxidizing or low-temperature laboratory conditions. Technologically, krypton is valued mainly for specialized lighting, gas lasers, insulating gas mixtures, and isotope applications rather than bulk chemical reactivity.

Krypton is a "noble" gas. It is characterized by its brilliant green and orange spectral lines.

The name derives from the Greek kryptos for "concealed" or "hidden". It was discovered in liquefied atmospheric air by the Scottish chemist William Ramsay and the English chemist Morris William Travers in 1898. A wavelength in the atomic spectrum of 86Kr is a fundamental standard of length.

Krypton was discovered on May 30, 1898 by Sir William Ramsay, a Scottish chemist, and Morris M. Travers, an English chemist, while studying liquefied air. Small amounts of liquid krypton remained behind after the more volatile components of liquid air had boiled away. The earth's atmosphere is about 0.0001% krypton.

From the Greek word kryptos, hidden. Discovered in 1898 by Ramsay and Travers in the residue left after liquid air had nearly boiled away. In 1960 it was internationally agreed that the fundamental unit of length, the meter, should be defined in terms of the orange-red spectral line of 86Kr. This replaced the standard meter of Paris, which was defined in terms of a bar made of a platinum-iridium alloy. In October 1983, the meter, which originally was defined as being one ten millionth of a quadrant of the earth's polar circumference, was again redefined by the International Bureau of Weights and Measures as being the length of a path traveled by light in a vacuum during a time interval of 1/299,792,458 of a second.

Read about Krypton on Wikipedia

Images

Properties

Physical

Covalent radius 116 pm

Van der Waals radius 202 pm

Density

Molar volume 0.0322 L/mol

Phase at STP gas

Melting point -157.36 °C

Boiling point -153.42 °C

Thermal conductivity 0.009 W/(m·K)

Specific heat capacity 0.248 J/(g·K)

Molar heat capacity 20.786 J/(mol·K)

Crystal structure fcc

Chemical

Electronegativity (Pauling) 3

Electronegativity (Allen) 2.966

Electron affinity

Ionization energy (1st)

Ionization energy (2nd)

Ionization energy (3rd)

Ionization energy (4th)

Ionization energy (5th)

Oxidation states 0, +1, +2

Valence electrons 8

Electron configuration

Electron configuration (semantic)

Thermodynamic

Triple point (temperature) -157.36 °C

Triple point (pressure) 7.320000e+4 Pa

Critical point (temperature) -63.67 °C

Critical point (pressure) 5.525000e+6 Pa

Heat of fusion 0.01699746 eV

Heat of vaporization 0.09327875 eV

Heat of atomization 0 eV

Nuclear

Stable isotopes 5

Discovery year 1898

Abundance

Abundance (Earth's crust) 1.000e-4 mg/kg

Abundance (ocean)

Reactivity

N/A

Crystal Structure

Lattice constant a 572 pm

Electronic Structure

Electrons per shell 2, 8, 18, 8

Identifiers

CAS number 7439-90-9

Term symbol

InChI InChI=1S/Kr

InChI Key DNNSSWSSYDEUBZ-UHFFFAOYSA-N

Electron Configuration Measured

Ion charge

Protons 36

Electrons 36

Charge Neutral

Configuration Kr: 3d¹⁰ 4s² 4p⁶

[Ar] 3d¹⁰ 4s² 4p⁶

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶

Orbital diagram

↑↓

2/2

↑↓

2/2

↑↓

6/6

↑↓

2/2

↑↓

6/6

↑↓

2/2

↑↓

10/10

↑↓

6/6

Total electrons: 36 Unpaired: 0

Atomic model

Protons 36

Neutrons 48

Electrons 36

Mass number 84

Stability Stable

Isotopes change neutron count, mass, and stability — not the electron configuration of a neutral atom.

Schematic atomic model, not to scale.

Atomic Fingerprint

Emission / Absorption Spectrum

Emission Visible: 380–750 nm

Isotope Distribution

Mass number	Atomic mass (u)	Natural abundance	Half-life
80 Stable	79.91637808 ± 0.00000075	2.2860%	Stable
82 Stable	81.91348273 ± 0.00000094	11.5930%	Stable
83 Stable	82.91412716 ± 0.00000032	11.5000%	Stable
84 Stable	83.9114977282 ± 0.0000000044	56.9870%	Stable
86 Stable	85.9106106269 ± 0.0000000041	17.2790%	Stable

Measured

Phase / State

Gas 25 °C (298.15 K)

Reason: 178.4 °C above boiling point (-153.42 °C)

Melting point -157.36 °C

Boiling point -153.42 °C

Above boiling by 178.4 °C

0 K Current temperature: 25 °C 6000 K

Phase timeline

Schematic, not to scale

Solid

Liquid

Gas

Melting

Boiling

25°C

Solid

Liquid

Gas

Current

Phase transition points

Melting point Literature

-157.36 °C

Boiling point Literature

-153.42 °C

Current phase Calculated
Gas

Transition energies

Heat of fusion Literature

0.01699746 eV

Energy required to melt 1 mol at melting point

Heat of vaporization Literature

0.09327875 eV

Energy required to vaporize 1 mol at boiling point

Density

Reference density Literature

3.733 kg/m³

At standard conditions

Current density Estimated

3.425163 kg/m³

Estimated via ideal gas law at current T

Advanced

Triple point Literature

-157.36 °C

Critical point Literature

-63.67 °C

Atomic Spectra

Showing 10 of 36 Atomic Spectra. Sorted by ion charge (ascending).

Lines Holdings ?

Ion	Charge	Total lines	Transition probabilities	Level designations
Kr I	0	862	184	862
Kr II	+1	1178	20	1178
Kr III	+2	877	0	877
Kr IV	+3	485	0	485
Kr V	+4	174	0	174
Kr VI	+5	142	0	142
Kr VII	+6	73	0	73
Kr VIII	+7	177	0	177
Kr IX	+8	125	0	125
Kr X	+9	46	0	46

NIST Lines Holdings →

Levels Holdings ?

Ion	Charge	Levels
Kr I	0	528
Kr II	+1	163
Kr III	+2	123
Kr IV	+3	79
Kr V	+4	43
Kr VI	+5	45
Kr VII	+6	28
Kr VIII	+7	110
Kr IX	+8	58
Kr X	+9	36

NIST Levels Holdings →

36 Kr 83.798

Krypton — Atomic Orbital Visualizer

[Ar]4s23d104p6

Energy levels 2 8 18 8

Oxidation states 0, +1, +2

HOMO 4p n=4 · l=1 · m=-1

Krypton — Atomic Orbital Visualizer Preview

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36 Kr 83.798

Krypton — Crystal Structure Visualizer

Face-Centered Cubic · Pearson cF4

Experimental

Pearson cF4

Coord. № 12

Packing 74.000%

No crystal structure at standard conditions — gas at 298 K, 1 atm

Solid phase structure at 293 K

Krypton — Crystal Structure Visualizer Preview

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Compounds

83.800 u

80.917 u

84.913 u

83.911 u

85.911 u

79.916 u

78.920 u

88.918 u

86.913 u

87.914 u

77.920 u

81.913 u

76.925 u

75.926 u

82.914 u

Isotopes (5)

Naturally occurring krypton contains six stable isotopes. Seventeen other unstable isotopes are recognized. The spectral lines of krypton are easily produced and some are very sharp. While krypton is generally thought of as a rare gas that normally does not combine with other elements to form compounds, it now appears that the existence of some krypton compounds can exist. Krypton difluoride has been prepared in gram quantities and can be made by several methods. A higher fluoride of krypton and a salt of an oxyacid of krypton also have been reported. Molecule-ions of ArKr+ and KrH+ have been identified and investigated, and evidence is provided for the formation of KrXe or KrXe+.

Mass number	Atomic mass (u)	Natural abundance	Half-life	Decay mode
80 Stable	79.91637808 ± 0.00000075	2.2860% ± 0.0100%	Stable	stable
82 Stable	81.91348273 ± 0.00000094	11.5930% ± 0.0310%	Stable	stable
83 Stable	82.91412716 ± 0.00000032	11.5000% ± 0.0190%	Stable	stable
84 Stable	83.9114977282 ± 0.0000000044	56.9870% ± 0.0150%	Stable	stable
86 Stable	85.9106106269 ± 0.0000000041	17.2790% ± 0.0410%	Stable	stable

80 Stable

Atomic mass (u) 79.91637808 ± 0.00000075

Natural abundance 2.2860% ± 0.0100%

Half-life Stable

Decay mode

stable

82 Stable

Atomic mass (u) 81.91348273 ± 0.00000094

Natural abundance 11.5930% ± 0.0310%

Half-life Stable

Decay mode

stable

83 Stable

Atomic mass (u) 82.91412716 ± 0.00000032

Natural abundance 11.5000% ± 0.0190%

Half-life Stable

Decay mode

stable

84 Stable

Atomic mass (u) 83.9114977282 ± 0.0000000044

Natural abundance 56.9870% ± 0.0150%

Half-life Stable

Decay mode

stable

86 Stable

Atomic mass (u) 85.9106106269 ± 0.0000000041

Natural abundance 17.2790% ± 0.0410%

Half-life Stable

Decay mode

stable

Spectral Lines

Wavelength (nm)	Intensity	Ion stage	Type	Transition	Accuracy	Source
384.09 nm	N/A	ID 649	emission	3s2.3p2 3P → 3s2.3p2 3P	Measured	NIST
392.9 nm	N/A	Kr VIII	emission	3d10.8f 2F* → 3d10.9g 2G	Measured	NIST
392.9 nm	N/A	Kr VIII	emission	3d10.8f 2F* → 3d10.9g 2G	Measured	NIST
392.9 nm	N/A	Kr VIII	emission	3d10.8f 2F* → 3d10.9g 2G	Measured	NIST
429.9 nm	N/A	Kr VIII	emission	3d10.8g 2G → 3d10.9h 2H*	Measured	NIST
429.9 nm	N/A	Kr VIII	emission	3d10.8g 2G → 3d10.9h 2H*	Measured	NIST
430 nm	N/A	Kr VIII	emission	3d10.8g 2G → 3d10.9h 2H*	Measured	NIST
433.2 nm	N/A	Kr VIII	emission	3d10.8h 2H* → 3d10.9i 2I	Measured	NIST
433.2 nm	N/A	Kr VIII	emission	3d10.8h 2H* → 3d10.9i 2I	Measured	NIST
433.2 nm	N/A	Kr VIII	emission	3d10.8h 2H* → 3d10.9i 2I	Measured	NIST
433.77 nm	N/A	Kr VIII	emission	3d10.8i 2I → 3d10.9k 2K*	Measured	NIST
433.77 nm	N/A	Kr VIII	emission	3d10.8i 2I → 3d10.9k 2K*	Measured	NIST
433.77 nm	N/A	Kr VIII	emission	3d10.8i 2I → 3d10.9k 2K*	Measured	NIST
433.81 nm	N/A	Kr VIII	emission	3d10.8k 2K* → 3d10.9l 2L	Measured	NIST
433.81 nm	N/A	Kr VIII	emission	3d10.8k 2K* → 3d10.9l 2L	Measured	NIST
433.81 nm	N/A	Kr VIII	emission	3d10.8k 2K* → 3d10.9l 2L	Measured	NIST
464 nm	N/A	ID 672	emission	1s.5s 3S → 1s.5p 3P*	Measured	NIST
466.79 nm	N/A	Kr VIII	emission	3d10.10m 2M* → 3d10.12n 2N	Measured	NIST
466.79 nm	N/A	Kr VIII	emission	3d10.10m 2M* → 3d10.12n 2N	Measured	NIST
466.79 nm	N/A	Kr VIII	emission	3d10.10m 2M* → 3d10.12n 2N	Measured	NIST
510 nm	N/A	ID 672	emission	1s.4p 3P* → 1s.4d 3D	Measured	NIST
563 nm	N/A	Kr VIII	emission	3d10.8p 2P* → 3d10.8d 2D	Measured	NIST
565.6 nm	N/A	Kr VIII	emission	3d10.8d 2D → 3d10.9p 2P*	Measured	NIST
568.6 nm	N/A	Kr VIII	emission	3d10.8d 2D → 3d10.8f 2F*	Measured	NIST
572.7 nm	N/A	Kr VIII	emission	3d10.8d 2D → 3d10.8f 2F*	Measured	NIST
576.1 nm	N/A	Kr VIII	emission	3d10.8d 2D → 3d10.9p 2P*	Measured	NIST
578.5 nm	N/A	Kr VIII	emission	3d10.7f 2F* → 3d10.8d 2D	Measured	NIST
580.7 nm	N/A	Kr VIII	emission	3d10.8p 2P* → 3d10.8d 2D	Measured	NIST
583.2 nm	N/A	Kr VIII	emission	3d10.7f 2F* → 3d10.8d 2D	Measured	NIST
584.9 nm	N/A	Kr VIII	emission	3d10.8p 2P* → 3d10.8d 2D	Measured	NIST
605.6 nm	N/A	Kr VIII	emission	3d10.9k 2K* → 3d10.10l 2L	Measured	NIST
605.6 nm	N/A	Kr VIII	emission	3d10.9k 2K* → 3d10.10l 2L	Measured	NIST
605.6 nm	N/A	Kr VIII	emission	3d10.9k 2K* → 3d10.10l 2L	Measured	NIST
606.6 nm	N/A	Kr VIII	emission	3d10.9l 2L → 3d10.10m 2M*	Measured	NIST
606.6 nm	N/A	Kr VIII	emission	3d10.9l 2L → 3d10.10m 2M*	Measured	NIST
606.6 nm	N/A	Kr VIII	emission	3d10.9l 2L → 3d10.10m 2M*	Measured	NIST
637 nm	N/A	ID 647	emission	3p6.3d 2D → 3p6.3d 2D	Measured	NIST
719.57 nm	N/A	ID 674	emission	2p 2P* → 2s 2S	Measured	NIST

Extended Properties

Covalent Radii (Extended)

Covalent radius (Pyykkö)

Covalent radius (Pyykkö, double)

Covalent radius (Pyykkö, triple)

Van der Waals Radii

Bondi

Alvarez

UFF

MM3

Atomic & Metallic Radii

Atomic radius (Rahm)

Numbering Scales

Mendeleev

Pettifor

Glawe

Electronegativity Scales

Ghosh

Gunnarsson–Lundqvist

Robles–Bartolotti

Polarizability & Dispersion

Dipole polarizability

Dipole polarizability (unc.)

C₆

C₆ (Gould–Bučko)

Chemical Affinity

Proton affinity

Gas basicity

Noble Gas Properties

Density (25 °C) 3.427 g/L

Reactions

HALOGENS

KrF2

Phase Transitions & Allotropes

Melting point	115.78 K
Boiling point	119.73 K
Critical point (temperature)	209.48 K
Critical point (pressure)	5.53 MPa
Triple point (temperature)	115.77 K
Triple point (pressure)	73.53 kPa

Oxidation State Categories

+1 extended

+2 main

Advanced Reference Data

Screening Constants (8)

n	Orbital	σ
1	s	0.7684
2	p	3.953
2	s	9.602
3	d	15.3741
3	p	15.5658
3	s	14.9673
4	p	26.2308
4	s	24.6844

Isotope Decay Modes (55)

Isotope	Mode	Intensity
67	2p	37%
67	B+	—
68	B+	—
68	B+p	90%
68	p	—
69	B+	100%
69	B+p	94%
70	B+	100%
70	B+p	1.3%
71	B+	100%

X‑ray Scattering Factors (509)

Energy (eV)	f₁	f₂
10	—	0
10.1617	—	0
10.3261	—	0
10.4931	—	0
10.6628	—	0
10.8353	—	0
11.0106	—	0
11.1886	—	0
11.3696	—	0
11.5535	—	0

Additional Data

Estimated Crustal Abundance

The estimated element abundance in the earth's crust.

1×10-4 milligrams per kilogram

References (1)

[5] Krypton https://education.jlab.org/itselemental/ele036.html

Estimated Oceanic Abundance

The estimated element abundance in the earth's oceans.

2.1×10-4 milligrams per liter

References (1)

[5] Krypton https://education.jlab.org/itselemental/ele036.html

Sources

Sources of this element.

Krypton is present in the air to the extent of about 1 ppm. The atmosphere of Mars has been found to contain 0.3 ppm of krypton. Solid krypton is a white crystalline substance with a face-centered cubic structure which is common to all the "rare gases."

References (1)

[6] Krypton https://periodic.lanl.gov/36.shtml

Isotopes in Forensic Science and Anthropology

Information on the use of this element's isotopes in forensic science and anthropology.

85Kr (with a half-life of 10.7 years) has been used in atmospheric monitoring programs to track the effect of atomic facilities on the surrounding environment. 85Kr is co-generated with plutonium in the fuel elements of nuclear fission reactors and can be monitored at short distances (i.e. 1 to 5 km) from an area of clandestine plutonium separation from spent fuel from the nuclear reactor. The differences in 85Kr levels in the atmosphere have been used to estimate the amount of plutonium separated at weekly intervals. The production of plutonium for nuclear weapons and the output from commercial reprocessing plants have released large amounts of 85Kr into the atmosphere [283] [283] M. B. Kalinowski, H. Sartorius, S. Uhl, W. Weiss. J. Environ. Radioact.73, 203 (2004).[283] M. B. Kalinowski, H. Sartorius, S. Uhl, W. Weiss. J. Environ. Radioact.73, 203 (2004)..

References (2)

[283] M. B. Kalinowski, H. Sartorius, S. Uhl, W. Weiss. J. Environ. Radioact.73, 203 (2004).
[4] IUPAC Periodic Table of the Elements and Isotopes (IPTEI) https://doi.org/10.1515/pac-2015-0703

References

(9)

1 PubChem

Data deposited in or computed by PubChem

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2 Atomic Mass Data Center (AMDC), International Atomic Energy Agency (IAEA)

The half-life and atomic mass data was provided by the Atomic Mass Data Center at the International Atomic Energy Agency.

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3 IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW)

Krypton

Element data are cited from the Atomic weights of the elements (an IUPAC Technical Report). The IUPAC periodic table of elements can be found at https://iupac.org/what-we-do/periodic-table-of-elements/. Additional information can be found within IUPAC publication doi:10.1515/pac-2015-0703 Copyright © 2020 International Union of Pure and Applied Chemistry.

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4 IUPAC Periodic Table of the Elements and Isotopes (IPTEI)

The information are cited from Pure Appl. Chem. 2018; 90(12): 1833-2092, https://doi.org/10.1515/pac-2015-0703.

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License note: Copyright (c) 2020 International Union of Pure and Applied Chemistry. The International Union of Pure and Applied Chemistry (IUPAC) contribution within Pubchem is provided under a CC-BY-NC-ND 4.0 license, unless otherwise stated.

5 Jefferson Lab, U.S. Department of Energy

Krypton

Thomas Jefferson National Accelerator Facility (Jefferson Lab) is one of 17 national laboratories funded by the U.S. Department of Energy. The lab's primary mission is to conduct basic research of the atom's nucleus using the lab's unique particle accelerator, known as the Continuous Electron Beam Accelerator Facility (CEBAF). For more information visit https://www.jlab.org/

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License note: Please see citation and linking information: https://education.jlab.org/faq/index.html

6 Los Alamos National Laboratory, U.S. Department of Energy

Krypton

The periodic table at the LANL (Los Alamos National Laboratory) contains basic element information together with the history, source, properties, use, handling and more. The provenance data may be found from the link under the source name.

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7 NIST Physical Measurement Laboratory

Krypton

The periodic table contains NIST's critically-evaluated data on atomic properties of the elements. The provenance data that include data for atomic spectroscopy, X-ray and gamma ray, radiation dosimetry, nuclear physics, and condensed matter physics may be found from the link under the source name. Ref: https://www.nist.gov/pml/atomic-spectra-database

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8 PubChem Elements

Krypton

This section provides all form of data related to element Krypton.

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9 PubChem Elements

Krypton

The element property data was retrieved from publications.

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Last updated: May 1, 2026

Data verified: May 12, 2026

Content is reviewed against latest scientific data.