Krypton is a scarce atmospheric gas used in lamps and specialized lasers. Although it belongs to the noble-gas group, it can form compounds with fluorine. Light from krypton-86 once defined the meter, linking atomic spectra to the practical problem of making reproducible measurements.
FROM ELEMENT TO APPLICATION
AN ELEMENT IN CONTEXT
Why did the krypton meter specify an isotope?
The isotope krypton-86
FOLLOW THIS RELATIONSHIP
Select a reproducible atomic signal
The historical definition selected radiation from a particular transition in krypton-86, tying the reference to a specified isotope rather than a mixed sample.
Explore the model (optional)
KrFORM → INTERACTION → CONSEQUENCE
Follow the explanation in either direction. These are authored steps, not a physical clock.
Optional: check your understanding
USE THE EXPLANATION
What does krypton-86 specify?
Atomic identity, reference properties and structure models
INTERACTIVE 3D36 visible sites
An electron censusDrag to rotate · scroll or pinch to zoom
[Ar] 3d10 4s2 4p6. Grouping electrons by principal shell connects the neutral-atom configuration to periodic-table patterns.
What this representation means
A three-dimensional counting diagram. Dots are count markers, not measured electron positions; spherical placement and spacing are arbitrary. There are no electron trajectories here. Orbitals describe quantum states.
Ramsay and Travers searched for additional gases after argon's discovery suggested a new periodic family. In 1898 they obtained krypton while separating atmospheric material and recognized its distinct . That optical signature later supported precision measurement: a transition in krypton-86 became the basis of the meter in 1960. The journey connected separating a trace gas with replacing a physical length standard by an atomic reference.
1898
Krypton isolated
Ramsay and Travers identified a new gas through its characteristic spectrum.
1960
Meter definition adopted
An optical transition in krypton-86 supplied the reference for a new definition of length.
Krypton is a minor constituent of Earth's atmosphere and has also been detected in the Martian atmosphere. On Earth it can be separated during the processing of liquefied air. Its small atmospheric proportion makes separation important, even though the starting resource is ordinary air rather than an unusual deposit.
Krypton is a noble gas with low ordinary chemical reactivity and characteristic spectral lines when excited. Low reactivity is not absolute inability to form compounds: krypton difluoride has been prepared. The contrast shows why periodic families describe useful trends while still allowing element-specific exceptions and specialized chemical behavior.
Each section links its supporting references. Descriptions and diagrams were authored for this atlas. Source checks completed. Source checks dated 2026-09-06.
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Family labels and the group-3 layout are teaching conventions. A table position does not establish an unknown bulk property. Electronic configurations refer to neutral atoms; ions and material environments require their own account.
Read each reference property together with its units, conditions and the reference information below.
Not yet recorded: electron affinity, second ionization energy, ground-state term symbol, van der waals radius, thermal conductivity, specific heat capacity, electrical resistivity, crystal structure, lattice parameter a, space group, abundance in seawater, abundance in the universe, annual production, supply-risk listing, hazard classification, biological role, cas registry number, pubchem cid, wikidata item. These families are declared and awaiting an ingestion run against the source each names; they are listed here rather than shown as empty rows.
Physical
Intended reference: CRC Handbook of Chemistry and Physics · CRC Press
Phase at 20 °C
gas
293.15 K, 101.325 kPa
Melting point in K
115.79 K
at standard pressure unless noted
Boiling point in K
119.93 K
101.325 kPa
Density in g/cm³
0.00373 g/cm³
solids and liquids at 293 K; gases at 273 K and 101.325 kPa
Atomic and electronic
Intended reference: Pauling electronegativity scale · Widely tabulated; original in The Nature of the Chemical Bond
Electronegativity in Pauling
3 Pauling
Pauling scale
First ionization energy in kJ/mol
1351 kJ/mol
gas-phase neutral atom, ground state
Covalent radius in pm
116 pm
single-bond covalent radius
Common oxidation states
0, +2
states met in ordinary compounds; not exhaustive
Occurrence and identity
Intended reference: CRC Handbook of Chemistry and Physics · CRC Press
Abundance in the crust in mg/kg
0.0001 mg/kg
upper continental crust, mass fraction
Has stable isotopes
Yesderived
Discovery year in CE
1898 CEderived
WHERE IT SITS AMONG ITS NEIGHBORS
Electronegativity across period 4
Kr 3 Pauling · Krypton
Electronegativity across period 4. Exact values.
K
0.82
Ca
1
Sc
1.36
Ti
1.54
V
1.63
Cr
1.66
Mn
1.55
Fe
1.83
Co
1.88
Ni
1.91
Cu
1.9
Zn
1.65
Ga
1.81
Ge
2.01
As
2.18
Se
2.55
Br
2.96
Kr
3
Electronegativity down group 18
Kr 3 Pauling · Krypton
Electronegativity down group 18. Exact values.
Kr
3
Xe
2.6
The trend uses the same reference-property values as the periodic table. Elements with no recorded value are left out of the line rather than drawn at zero.
