What is the atomic number of Krypton?

Krypton has atomic number 36, meaning each neutral Krypton atom contains 36 protons in its nucleus.

What is the electron configuration of Krypton?

The full electron configuration is 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶. In noble-gas shorthand this is written [Ar]3d¹⁰4s²4p⁶. Krypton's outermost shell is completely filled, making it chemically inert.

Is Krypton radioactive?

Naturally occurring Krypton is not significantly radioactive. It has six stable isotopes (⁷⁸Kr through ⁸⁶Kr). The radioisotope ⁸⁵Kr is produced by nuclear fission and has a half-life of about 10.8 years.

What is Krypton used for?

Krypton is used in high-performance lighting (krypton fluoride lasers, energy-saving light bulbs), double-glazed window insulation, and scientific metrology. The krypton-86 spectral line was historically used to define the meter.

Why is Krypton a noble gas?

Krypton belongs to Group 18 (the noble gases) because its outermost electron shell (n=4) is completely filled with 8 electrons (4s²4p⁶). This stable octet makes Krypton extremely unreactive under normal conditions.

What is the standard atomic weight of Krypton?

The standard atomic weight of Krypton is 83.798(2) u (unified atomic mass units), as determined by the International Union of Pure and Applied Chemistry (IUPAC).

Krypton Element Properties

Name: Krypton Element Properties
Availability: InStock
Author: Nham Vu

Full reference card for Krypton (Kr, Z=36): atomic data, physical constants, electron configuration, isotopes, and chemistry facts.

36 Kr 83.798

Krypton

Noble Gas — Group 18, Period 4 — Block p

Colorless, odorless, inert noble gas. Discovered in 1898 by William Ramsay and Morris Travers through fractional distillation of liquid air. The name derives from the Greek kryptos (“hidden”).

Noble Gas Non-metal Diamagnetic Gas at STP

Atomic Properties

Atomic Number (Z)	36
Standard Atomic Weight	83.798(2) u
Atomic Radius (van der Waals)	202 pm
Covalent Radius	116 pm
Electronegativity (Pauling)	3.00
1st Ionization Energy	1350.8 kJ/mol
2nd Ionization Energy	2350.4 kJ/mol
Electron Affinity	< 0 (no stable anion)
Oxidation States	0 (typically); +2 in KrF₂

Physical Properties

Phase at STP	Gas
Density (at 0 °C, 1 atm)	3.749 g/L
Melting Point	−157.37 °C (115.78 K)
Boiling Point	−153.34 °C (119.81 K)
Triple Point	115.775 K, 73.53 kPa
Critical Temperature	209.48 K
Critical Pressure	5.525 MPa
Heat of Fusion	1.64 kJ/mol
Heat of Vaporization	9.08 kJ/mol
Molar Heat Capacity (Cp)	20.95 J/(mol·K)
Thermal Conductivity	9.43 mW/(m·K)
Speed of Sound (gas, 23°C)	220 m/s

Identifiers & Classification

CAS Number

7439-90-9

PubChem CID

5416

InChI

InChI=1S/Kr

RTECS

OC9300000

Electron Configuration

Full Configuration	1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶
Noble Gas Shorthand	[Ar]3d¹⁰4s²4p⁶
Valence Electrons	8 (full octet)
Shells (K L M N)	2, 8, 18, 8
Valence Shell	n = 4
Highest Occupied Orbital	4p⁶
HOMO–LUMO Gap	Very large (chemically inert)
Magnetic Order	Diamagnetic

Electron Shell Diagram

Shells: K(2) — L(8) — M(18) — N(8)

Orbital Breakdown

Subshell	Electrons	Shell (n)	Orbital Type	Cumulative
1s²	2	1	s	2
2s²	2	2	s	4
2p⁶	6	2	p	10
3s²	2	3	s	12
3p⁶	6	3	p	18
3d¹⁰	10	3	d	28
4s²	2	4	s	30
4p⁶	6	4	p	36

Krypton Isotopes

6 stable isotopes (bold)

Nuclide	Mass Number	Atomic Mass (u)	Abundance (%)	Half-life	Decay Mode
⁷⁸Kr	78	77.9204	0.355	Stable	—
⁷⁹Kr	79	78.9201	—	35.04 h	EC, β⁺
⁸⁰Kr	80	79.9164	2.286	Stable	—
⁸¹Kr	81	80.9166	—	229,000 y	EC
⁸²Kr	82	81.9135	11.593	Stable	—
⁸³Kr	83	82.9141	11.500	Stable	—
⁸⁴Kr	84	83.9115	56.987	Stable	—
⁸⁵Kr	85	84.9125	—	10.776 y	β⁻
⁸⁶Kr	86	85.9106	17.279	Stable	—
⁸⁷Kr	87	86.9134	—	76.3 min	β⁻
⁸⁸Kr	88	87.9145	—	2.84 h	β⁻

Abundances are IUPAC 2021 standard values. EC = electron capture. β⁻ = beta-minus decay. β⁺ = beta-plus decay.

Major Emission Lines (visible spectrum)

Wavelength (nm)	Color Region	Relative Intensity
427.40	Violet	300
431.96	Violet	200
436.26	Violet	150
445.39	Blue-Violet	120
450.24	Blue	90
473.90	Blue	200
557.03	Green-Yellow	600
587.09	Yellow	300
760.15	Near-IR	1000
819.00	Near-IR	800

Wavelengths in air at standard conditions. Intensity values are approximate relative values from NIST Atomic Spectra Database. Near-IR lines at 760 nm and 819 nm are the strongest overall Krypton transitions.

Historical Note: The Krypton Meter Standard

From 1960 to 1983, the international meter was defined as exactly 1,650,763.73 wavelengths of the orange-red emission line of ⁸⁶Kr (605.780 nm) in vacuum. This spectroscopic standard replaced the physical platinum-iridium prototype meter bar and was itself replaced in 1983 by the current speed-of-light definition (c = 299,792,458 m/s).

Copied!

Summary

Full reference card for Krypton (Kr, Z=36): atomic data, physical constants, electron configuration, isotopes, and chemistry facts.

How it works

Browse the property cards to find atomic, physical, or electronic data for Krypton.
Use the section tabs to switch between Overview, Electron Configuration, Isotopes, and Spectral Lines.
Click any value to copy it to the clipboard.
Use the isotope table to compare mass number, natural abundance, and half-life.
Toggle the electron shell diagram to visualize how electrons are distributed.

Use cases

Quick reference for chemistry homework or university coursework.
Verifying Krypton data for laboratory or research notes.
Teaching periodic table concepts including noble gases and electron configurations.
Preparing for standardized tests that include periodic table questions.
Comparing Krypton properties with neighboring noble gases (Argon, Xenon).
Looking up spectral emission lines for spectroscopy experiments.

Frequently Asked Questions

Last updated: 2026-06-18 · Reviewed by Nham Vu