Krypton

Krypton (Kr) is a noble gas with atomic number 36 and an atomic mass of 83.798. Its electron configuration is [Ar] 3d10 4s2 4p6, which gives it 8 valence electrons.

Krypton key data

Symbol	Kr
Atomic number	36
Atomic mass (standard atomic weight)	83.798
Molar mass	83.798 g/mol
Protons	36
Neutrons (most abundant isotope, krypton-84)	48
Electrons (neutral atom)	36
Valence electrons	8
Category	Noble gas
Period	4
Group	18
Block	p-block
Noble gas notation	[Ar] 3d10 4s2 4p6
Full electron configuration	1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6
Electrons per shell	2, 8, 18, 8

Atomic mass: IUPAC CIAAW abridged standard atomic weights, 2024. Most abundant isotope: NIST Atomic Weights and Isotopic Compositions.

Measured properties of krypton

From PubChem, the US National Institutes of Health. Public domain. PubChem’s periodic table gives no value for the rows not shown.

Melting point	115.79 K (−157.36 °C), 96th of 103 by melting point
Boiling point	119.93 K (−153.22 °C), 86th of 93 by boiling point
Density	0.003733 g/cm³, 88th of 96 by density
State at room temperature	Gas
Electronegativity	3 (Pauling), 5th of 95 by electronegativity
Van der Waals radius	202 pm, joint 57th of 99 by atomic radius
First ionisation energy	14 eV (1350 kJ/mol), 6th of 102 by first ionisation energy
Common oxidation states	0
Discovered	1898

Each rank counts down from the highest value, among the elements PubChem’s table gives one for, and links to that property ranked across the whole table. All of them are collected under periodic trends.

Krypton electron configuration

The full electron configuration of krypton is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6. With the noble-gas core collapsed it is [Ar] 3d10 4s2 4p6, and the outermost subshell is 4p6.

Bohr model of krypton (Kr): a nucleus and four shells holding 2, 8, 18 and 8 electrons from the inside out. — Bohr model of krypton (Kr). Image © ScienceQuest, CC BY 4.0: free to reuse with credit to ScienceQuest and a link to this page, as the image licence explains.

Orbital box diagram of krypton (Kr), 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6: one box per orbital, filled by Hund’s rule, showing every orbital drawn holds a pair of electrons. — Orbital diagram of krypton (Kr). Image © ScienceQuest, CC BY 4.0: free to reuse with credit to ScienceQuest and a link to this page, as the image licence explains.

Why group and block follow from this is set out in how the periodic table maps electron configuration, and the electron configuration of every element is listed on one page.

Mass of one krypton atom

A molar mass is grams per mole, so dividing by the Avogadro constant gives the mass of a single atom, or for an element with more than one natural isotope the average mass of its atoms, and the reciprocal gives how many atoms sit in a gram.

Mass of one atom

one atom = 83.798 / (6.02214076 × 10²³)
= 1.3915 × 10⁻²² g

Atoms in one gram

atoms per gram = 6.02214076 × 10²³ / 83.798
= 7.1865 × 10²¹ atoms

Krypton on the periodic table

Krypton is in period 4, group 18, in the p-block.

The other elements of group 18 are helium, neon, argon, xenon, radon and oganesson.