What are the oxidation states of krypton?

Krypton has two known oxidation states: 0 (elemental krypton — the most stable and common form) and +2 (found in KrF₂, krypton difluoride). No other oxidation states have been reliably characterized for krypton under normal or laboratory conditions.

Why does krypton have so few oxidation states compared to transition metals?

Krypton is a noble gas with a completely filled valence shell (4s²4p⁶). This stable octet configuration makes electron loss or sharing energetically very unfavorable. The ionization energies of krypton are extremely high, and there are no low-lying empty orbitals available for bonding under ordinary conditions. Only the exceptionally electronegative fluorine atom can force krypton into the +2 state.

What is the oxidation state of krypton in KrF₂?

In KrF₂, fluorine is always -1 (the most electronegative element). With two fluorine atoms the total is -2. The molecule is neutral, so Kr + 2(-1) = 0, giving Kr = +2.

Is KrF₂ stable at room temperature?

No. KrF₂ is thermodynamically unstable and decomposes back to krypton gas and fluorine gas at room temperature. It must be stored at low temperatures and handled with extreme care. Its formation requires UV irradiation or electric discharge of a Kr/F₂ mixture at −196 °C (liquid nitrogen temperature).

Can krypton have a negative oxidation state?

No. Krypton has no known compounds where it carries a negative oxidation state. Negative oxidation states require an element to be more electronegative than its bonding partner, but krypton, as a noble gas, does not form stable bonds with less electronegative elements.

How does krypton compare to xenon in terms of oxidation states?

Xenon (Z=54) is significantly more reactive than krypton and exhibits oxidation states of 0, +2, +4, +6, and +8, with a much wider range of stable compounds (XeF₂, XeF₄, XeO₃, XeO₄, etc.). Krypton, with higher ionization energy relative to its period, is limited to 0 and +2. Argon (Z=18) has no confirmed non-zero oxidation states at all.

Krypton Oxidation States

Name: Krypton Oxidation States
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Author: Nham Vu

Krypton has two known oxidation states: 0 (elemental) and +2 (in KrF₂, krypton difluoride). This reference explains both states, why Kr is nearly inert, and how KrF₂ forms under extreme conditions.

Atomic # 36 Kr Krypton

Atomic Mass

83.798 u

Group

18 (Noble Gas)

Period

Block

p-block

Electronegativity

3.00 (Pauling)

Oxidation States

0, +2

Oxidation States

Krypton has only two known oxidation states. Click a card to see details.

Oxidation State 0 Elemental Krypton

By convention, any element in its pure elemental form carries an oxidation state of 0 — no electron transfer occurs when an atom bonds only to identical atoms. Krypton gas (Kr) is a monoatomic noble gas under standard conditions, so every Kr atom in the atmosphere or in a gas cylinder has oxidation state 0. This is by far the most common and stable state for krypton.

How to Assign This State

Pure elemental substance rule: any form of krypton that contains only Kr atoms (gas, liquid, solid) carries oxidation state 0. No calculation is needed.

Examples

Form	Assignment	Notes
Kr(g)	Elemental gas → Kr = 0	Colorless, odorless noble gas. 1.14 ppm in Earth's atmosphere by volume.
Kr(l)	Elemental liquid → Kr = 0	Liquid krypton below −153.4 °C (bp). Used in research detectors (e.g., dark matter experiments).
Kr(s)	Elemental solid → Kr = 0	Solid krypton below −157.4 °C (mp). Face-centered cubic crystal structure.

Common Uses of Elemental Krypton

High-performance lighting: krypton-filled incandescent and halogen lamps (brighter, longer-lived filaments)
Double-glazed window insulation (Kr gas between panes has lower thermal conductivity than air)
Krypton-86 spectral line was the international definition of the metre from 1960 to 1983
Liquid krypton detectors in particle physics and dark matter search experiments
Excimer lasers (KrF laser, 248 nm) for semiconductor lithography and eye surgery

Oxidation State +2 KrF₂ and related species

The +2 state is the only confirmed non-zero oxidation state of krypton. It occurs exclusively when krypton bonds to fluorine, the most electronegative element on the periodic table. Fluorine is the only atom with sufficient electronegativity (3.98 Pauling) to pull electron density away from a noble gas atom and force it into a positive oxidation state. The sole well-characterized krypton compound is krypton difluoride (KrF₂), first synthesized in 1963.

How to Assign This State in KrF₂

1F is always −1 (most electronegative element).
2Two F atoms: 2 × (−1) = −2 total.
3Molecule is neutral: Kr + (−2) = 0.
4Kr = +2.

Known +2 Krypton Compound

Formula	Name	Assignment	Notes
KrF₂	Krypton Difluoride	2(−1) + Kr = 0 → Kr = +2	White solid; linear geometry (F−Kr−F). Thermodynamically unstable; decomposes above −10 °C. Strong fluorinating agent.

How KrF₂ Is Made

KrF₂ cannot be synthesized by simply mixing krypton and fluorine gases at room temperature — the reaction is endothermic (ΔHf° ≈ +60 kJ/mol), so energy must be supplied. Synthesis methods include:

UV photolysis of a Kr/F₂ mixture at −196 °C (liquid nitrogen temperature)
Electric discharge through a Kr/F₂ mixture at low temperature
High-energy particle irradiation of Kr/F₂ mixtures

Once formed, KrF₂ decomposes spontaneously above about −10 °C and must be stored cold. It is a powerful fluorinating and oxidizing agent but has very limited practical applications due to its instability.

Other Reported +2 Species

KrF⁺ and Kr₂F₃⁺ (ionic species detected in superacid media; not stable isolable compounds)
HKrF and HKrCl (matrix-isolated at 10 K; decompose instantly above cryogenic temperatures)
KrO (calculated but not yet experimentally confirmed)

Why Does Krypton Have So Few Oxidation States?

Krypton's electron configuration ends in a completely filled 4p subshell (4s²4p⁶). This closed-shell arrangement is exceptionally stable. Three factors make non-zero oxidation states almost impossible for Kr:

High Ionization Energy

Removing an electron from Kr requires 1,350 kJ/mol (1st IE). This is the energy barrier that must be overcome to form a Kr⁺ species or any bond where Kr loses electron density.

No Low-Lying Empty Orbitals

The 4d orbitals of krypton are too high in energy (unlike xenon's 5d) to participate meaningfully in bonding. This limits krypton to the +2 state at most, while xenon can reach +8.

Only F Can Force a Bond

Fluorine's extreme electronegativity (3.98) and small size allow it to polarize electron density from even noble gas atoms. No other element manages this with krypton under accessible conditions.

Noble Gas Comparison: Group 18 Oxidation States

Element	Z	Known Oxidation States	Notes
Helium	2	0 only	No confirmed compounds. Highest ionization energy of all elements.
Neon	10	0 only	No confirmed compounds. No accessible d orbitals.
Argon	18	0 only	ArF and ArH⁺ detected in cryogenic matrix; not stable.
Krypton	36	0, +2	KrF₂ is the sole stable compound. +2 requires extreme synthesis conditions.
Xenon	54	0, +2, +4, +6, +8	Rich chemistry: XeF₂, XeF₄, XeO₃, XeO₄, XeOF₄, etc. Far more accessible than Kr compounds.
Radon	86	0, +2 (inferred)	Radioactivity limits experimental study. RnF₂ inferred by analogy.

Oxidation State Summary

State	Stability	Key Example	Notes
0	Dominant	Kr(g)	Elemental krypton. Assigned by convention; no bonding partner.
+2	Very rare	KrF₂	Requires fluorine and extreme synthesis conditions. Thermally unstable.

Summary

How it works

Review the two known oxidation states (0 and +2) in the state cards.
Click a state card to expand its detail section with description, compound data, and assignment steps.
Read the "Why so few states?" section to understand the role of noble gas electron configuration.
Use the comparison table to see how krypton differs from its neighbors xenon and argon.

Use cases

Students studying noble gas chemistry and exceptions to inertness.
Chemistry teachers preparing lessons on Group 18 oxidation states.
Learners working through redox problems that include KrF₂.
Anyone comparing the reactivity of krypton, xenon, and argon.
Quick reference when assigned an oxidation state problem involving a noble gas.

Frequently Asked Questions

Last updated: 2026-07-23 · Reviewed by Nham Vu