Krypton (Kr)

Krypton is a noble gas with atomic number 36, in period 4 and group 18 of the periodic table. Its atomic mass is 83.798 u and its electron configuration is [Ar] 3d¹⁰ 4s² 4p⁶. Gas at 25 °C.

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Key facts

Atomic number	36
Atomic mass	83.798 u
Category	Noble Gas
Period	4
Group	18
Block	p
Electron configuration	[Ar] 3d¹⁰ 4s² 4p⁶
Electrons per shell	2, 8, 18, 8
Electronegativity (Pauling)	3
Oxidation states	+2common in bold
State at 25 °C	Gas
Melting point	115.79 K−157.36 °C
Boiling point	119.93 K−153.22 °C
Density	3.75 g/L

Atomic properties

First ionization energy	14 eV
Electron affinity	0 kJ/mol
Atomic radius	88 pm
Covalent radius	116 pm
Van der Waals radius	202 pm
Common ions	---
Protons, neutrons, electrons	36, 48, 36

Physical and thermal properties

Molar volume	27.99 cm³/mol
Heat of fusion	1.64 kJ/mol
Heat of vaporization	9.02 kJ/mol
Specific heat	248.05 J/(kg·K)
Thermal conductivity	0.00943 W/(m·K)
Thermal expansion	---
Mohs hardness	---
Young’s modulus	---
Crystal structure	Face-centered cubic
Magnetic type	Diamagnetic

Identification and history

CAS number	7439-90-9
Latin name	Krypton
Discovered by	W. Ramsay & M. Travers · 1898
Named by	---

Natural isotopes

Isotope	Mass (u)	Abundance
⁷⁸Kr	77.920366	0.355 %
⁸⁰Kr	79.916378	2.286 %
⁸²Kr	81.913481	11.593 %
⁸³Kr	82.914127	11.5 %
⁸⁴Kr	83.911498	56.987 %
⁸⁶Kr	85.910611	17.279 %

Data checked against PubChem (NIH), IUPAC, the NIST Atomic Spectra Database and the IAEA (NUBASE and AME), the same data you see in the app.

A dash (---) means there is no reliable published measurement. The app never makes one up.

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