Atomic / phase data
Reference values are evaluated.
FCC solid
Stable low-pressure solid is FCC.
KrF2 chemistry
Krypton difluoride is experimentally established.
Metrology history
86Kr metre-definition history is documented.
Geography
Atmospheric occurrence is global/conceptual rather than pinned.
The lens describes evidence status, not confidence theatre. “Unknown” is kept unknown, and teaching schematics are not presented as direct measurements.
Krypton (Kr)
Krypton is element 36, a rare atmospheric noble gas with a closed 4p shell. It is colorless as an ordinary gas, produces distinctive emission when excited, forms rare fluorine compounds, and once helped define the metre through ⁸⁶Kr spectroscopy.
Krypton atomic number, mass, electron configuration and key properties
Krypton: quick answers
How many protons, neutrons and electrons does krypton have?
Krypton’s atomic number is 36, so every krypton atom has 36 protons, and a neutral atom also has 36 electrons. Its most common natural isotope, krypton-84, has 48 neutrons (other isotopes have different neutron counts).
What is the symbol for krypton?
The chemical symbol for krypton is Kr.
Is krypton a solid, liquid or gas at room temperature?
Krypton is a gas at room temperature (about 25 °C).
What family (group) is krypton in?
Krypton is a noble gas, in group 18, period 4 of the periodic table.
How many valence electrons does krypton have?
Krypton has 8 valence electrons, the electrons in its outer shell, which matches its position in group 18.
What is the electron configuration of krypton?
The ground-state electron configuration of krypton is [Ar] 3d¹⁰ 4s² 4p⁶.
From atomic number to chemistry
Read these as a chain of causes, not as isolated facts. Each step links to the concept hub if you want the underlying idea explained.
36 protons define krypton.
The ground-state configuration provides the starting point for its chemistry.
Periodic position organizes recurring chemistry and trends.
The teaching nucleus is one isotope, not the relative atomic mass.
Phase boundaries are condition-dependent and evidence-labelled.
Krypton in its period and family
Krypton is the Period 4 noble gas, between bromine and rubidium and below argon. Greater polarizability than lighter noble gases makes limited chemistry possible.
Krypton Visual Lab
Inspect the closed 4p shell, compare colorless gas with excited emission and KrF₂ chemistry, freeze an FCC solid, and follow krypton from trace air separation to lighting, lasers and metrology history.
Every mark points to one exact feature
The numbered markers explain the same information system used throughout Element Lookup. Unknown or predicted fields remain visibly labelled rather than being replaced with guesses.
Krypton in one minute
Atomic number 36 means 36 protons.
Neutral krypton has a closed [Ar]3d¹⁰4s²4p⁶ configuration.
Krypton is only about one part per million of the atmosphere.
Krypton can form compounds such as KrF₂ under suitable conditions.
From 1960 to 1983, a spectral line of ⁸⁶Kr was used in the definition of the metre.
Shell rings organize electron counts. They are not electron trajectories or orbital shapes.
2 · 8 · 18 · 8 electrons
Atomic 4p clouds visualize occupancy. The glow in a discharge is an excited-state spectrum, and KrF₂ bonding is a molecular electronic-structure problem rather than a colored orbital picture.
Solid krypton adopts a stable FCC rare-gas structure under ordinary low-pressure conditions. The viewer is a teaching cell; metastable structures under special growth conditions are outside this basic model.. The viewer is evidence-aware: measured structures are identified as such; unknown bulk structures stay unknown.
Teaching visualization; not a literal finite sample or thermal trajectory.What this model does—and does not—show
Atomic 4p clouds visualize occupancy. The glow in a discharge is an excited-state spectrum, and KrF₂ bonding is a molecular electronic-structure problem rather than a colored orbital picture.
Where do I meet krypton?
Clickable learning cards connect the element to materials, environment, technology, biology or research - depending on what the evidence actually supports.
Lighting
Krypton is used in selected high-performance lamps and flash lamps.
Colorless noble gas → excited spectrum → KrF₂ chemistry
Krypton is mostly inert, but both spectroscopy and rare compound chemistry reveal more than the “noble gases never react” shortcut.
Closed-shell noble gas
Neutral krypton has a filled 4p6 outer shell.
Argon, krypton and xenon
Compare nearby elements to see which patterns repeat and which properties remain element-specific.
| Outer shell | 3p⁶ |
|---|---|
| Chemistry | very limited |
| Outer shell | 4p⁶ |
|---|---|
| Compound | KrF₂ known |
| Outer shell | 5p⁶ |
|---|---|
| Chemistry | many compounds |
Krypton properties: atomic, physical, thermal and chemical
Categories follow the science of this element rather than a fixed decorative template. Each row carries condition/provenance context and an evidence label; unknown values stay unknown.
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| Atomic number | 36 | Source-reviewed; see Sources below | Evaluated |
| Relative atomic mass | 83.798 | Source-reviewed; see Sources below | Evaluated |
| Ground-state electron configuration | [Ar] 3d¹⁰ 4s² 4p⁶ | Source-reviewed; see Sources below | Evaluated |
| Group / period / block | Group 18 · Period 4 · p-block | Periodic-table placement | Evaluated |
| Electronegativity | Unknown | Source-reviewed; see Sources below | Unknown |
| Reference isotope | ⁸⁴Kr | Source-reviewed; see Sources below | Evaluated |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| State context | Colorless monatomic gas at 20 °C | Source-reviewed; see Sources below | Evaluated |
| Density | 0.003425 g/cm³ | Source-reviewed; see Sources below | Evaluated |
| Material / molecular structure | Solid krypton · face-centred cubic | Solid krypton adopts a stable FCC rare-gas structure under ordinary low-pressure conditions. The viewer is a teaching cell; metastable structures under special growth conditions are outside this basic model. | Measured |
| Classification | Noble gas | Periodic-table / chemistry classification | Evaluated |
| Structure-model scope | Solid krypton adopts a stable FCC rare-gas structure under ordinary low-pressure conditions. The viewer is a teaching cell; metastable structures under special growth conditions are outside this basic model. | Teaching visualization; exact crystallographic coordinates are not implied unless stated. | Reviewed |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| Melting / transition reference | 115.78 K | Source-reviewed; see Sources below | Evaluated |
| Boiling / gas reference | 119.735 K | Source-reviewed; see Sources below | Evaluated |
| Phase-path context | At approximately standard pressure, krypton is solid below about 115.78 K, liquid to about 119.735 K, and gaseous above. Its normal liquid interval is narrow. | Shared phase registry drives the slider, regions and markers. | Evaluated |
| Condition warning | Temperature and pressure define phase behavior; purity/allotropy may matter. | Teaching condition statement | Reviewed |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| Common oxidation states | +2 in rare compounds; 0 as elemental gas | Source-reviewed; see Sources below | Evaluated |
| Ion / common ion context | No common stable monatomic ion in ordinary chemistry | Source-reviewed; see Sources below | Evaluated |
| Periodic chemistry context | Krypton is the Period 4 noble gas, between bromine and rubidium and below argon. Greater polarizability than lighter noble gases makes limited chemistry possible. | Element-specific interpretation | Reviewed |
| Chemistry caution | Elemental form, ions and compounds are distinct chemical objects. | Interpretive teaching rule | Reviewed |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| ⁸⁴Kr | Stable · most abundant natural isotope | Reference teaching nucleus: 36 protons and 48 neutrons. | Evaluated |
| ⁸⁶Kr | Stable natural isotope | Historically central to the 1960-1983 metre definition. | Evaluated |
| ⁸²Kr and ⁸³Kr | Stable natural isotopes | Important parts of the natural mixture used in spectroscopy and analytical work. | Evaluated |
| ⁸⁵Kr | Radioactive trace isotope | A fission-product noble gas used in atmospheric/nuclear monitoring contexts. | Evaluated |
| Teaching nucleus | ⁸⁴Kr · 36 protons + 48 neutrons | Reference isotope used in the nucleus model | Reviewed |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| Page evidence note | Atomic, phase, atmospheric and isotope values are evaluated/measured. KrF₂ is experimentally established chemistry. Atmospheric occurrence is conceptual; country pins would falsely imply deposits. | Evidence summary for this guide | Reviewed |
| Structure evidence | Solid krypton adopts a stable FCC rare-gas structure under ordinary low-pressure conditions. The viewer is a teaching cell; metastable structures under special growth conditions are outside this basic model. | Measured structure, labelled schematic, prediction or explicit unknown as applicable. | Reviewed |
| Map evidence rule | Real pins are reviewed examples; conceptual layers are used when pins would mislead. | Geography Explorer 2.0 | Reviewed |
| Source set | 3 primary/reference links listed below | Open the Sources section for the actual references. | Reviewed |
Is Krypton a solid, liquid or gas? State at temperature
At approximately standard pressure, krypton is solid below about 115.78 K, liquid to about 119.735 K, and gaseous above. Its normal liquid interval is narrow.
Where on Earth is Krypton found or produced?
Who discovered Krypton, and when?
William Ramsay and Morris Travers discovered krypton in the residue left after evaporating liquid air in London.
Spectroscopy and isotope research established krypton’s noble-gas identity and isotopic mixture.
The metre was defined using a precise wavelength of radiation from krypton-86.
Krypton is used in specialty lighting, lasers, glazing and scientific instrumentation.
From trace atmospheric gas to purified krypton: high-level context
Krypton is a trace atmospheric constituent, so the atmosphere is the meaningful global reservoir rather than a mine map.
Large cryogenic air-separation systems concentrate noble-gas fractions during oxygen/nitrogen production.
Further fractional separation and purification isolate krypton for specialty markets.
Finished gas is used in lamps, lasers, glazing and scientific applications; rare krypton chemistry requires specialized laboratory conditions.
What is krypton used for?
Lighting & flash lamps
Krypton is used in selected high-intensity and high-efficiency light sources.
Excimer lasers
KrF excimer lasers are important ultraviolet sources in specialized industrial/scientific systems.
High-performance glazing
Krypton gas can improve thermal performance in narrow insulating-glass cavities.
Scientific instruments
Krypton isotopes and spectra are used in analytical, atmospheric and nuclear-science measurements.
Krypton isotopes and natural abundance
⁸⁴Kr
Stable · most abundant natural isotopeReference teaching nucleus: 36 protons and 48 neutrons.
⁸⁶Kr
Stable natural isotopeHistorically central to the 1960-1983 metre definition.
⁸²Kr and ⁸³Kr
Stable natural isotopesImportant parts of the natural mixture used in spectroscopy and analytical work.
⁸⁵Kr
Radioactive trace isotopeA fission-product noble gas used in atmospheric/nuclear monitoring contexts.
Five-question Krypton check
Atomic number?
Outer shell?
Can krypton form a compound?
Industrial source?
Historical isotope-metrology link?
Krypton questions students commonly ask
Each answer starts with the direct fact, then explains the chemistry, evidence or material context so the result is understandable rather than merely memorized.
What is krypton’s atomic number?
Short answer: 36.
Atomic number is defined by proton count, so 36 protons are what make an atom krypton. A neutral krypton atom also has 36 electrons, while isotopes can have different neutron counts without changing the element.
Key point: Atomic number = proton count.
How many valence electrons does krypton have?
Short answer: Eight in the 4s²4p⁶ outer shell.
The neutral-atom ground-state reference used on this page is [Ar] 3d¹⁰ 4s² 4p⁶. This is an isolated-atom reference: bonding and ion formation can change which outer electrons are present or chemically active. The listed common oxidation-state context is +2 in rare compounds; 0 as elemental gas, which helps connect the atomic configuration to ordinary chemistry without treating electron counting as a single universal rule.
Key point: Electron configuration is a ground-state atomic reference, not a literal picture of every compound.
What is krypton used for?
Short answer: Specialty lighting, flash lamps, excimer lasers, high-performance glazing and scientific measurement.
Lighting & flash lamps: Krypton is used in selected high-intensity and high-efficiency light sources. Excimer lasers: KrF excimer lasers are important ultraviolet sources in specialized industrial/scientific systems. Krypton is chemically quiet, not chemically impossible. KrF₂ is a real compound, while most everyday krypton use still relies on the physical properties of the elemental noble gas.
Key point: Always distinguish the pure element from the compound, alloy, isotope or device material that actually performs the application.
Is krypton a metal?
Short answer: No. It is a noble gas.
This guide classifies Krypton as a noble gas. Its periodic position is Period 4, p-block, Group 18. Krypton is the Period 4 noble gas, between bromine and rubidium and below argon. Greater polarizability than lighter noble gases makes limited chemistry possible.
Key point: Periodic-table classification describes recurring atomic/chemical behavior; it does not make every element in a column physically identical.
Can krypton form compounds?
Short answer: Yes. Krypton difluoride, KrF₂, is a well-established example under suitable conditions.
Krypton is chemically quiet, not chemically impossible. KrF₂ is a real compound, while most everyday krypton use still relies on the physical properties of the elemental noble gas. High-performance glazing Krypton gas can improve thermal performance in narrow insulating-glass cavities.
Key point: The pure element, its ions, compounds and alloys are different materials and should not be treated as interchangeable.
How was krypton connected to the metre?
Short answer: From 1960 to 1983, the metre was defined by a specified number of wavelengths of a krypton-86 spectral line.
From 1960 to 1983, a spectral line of ⁸⁶Kr was used in the definition of the metre. Krypton is element 36, a rare atmospheric noble gas with a closed 4p shell. It is colorless as an ordinary gas, produces distinctive emission when excited, forms rare fluorine compounds, and once helped define the metre through ⁸⁶Kr spectroscopy.
Key point: Use the direct answer together with the material, isotope and evidence context shown elsewhere on the page.
Scientific sources for Krypton
- Royal Society of Chemistry - Krypton
- NIST - Atomic Data for Krypton
- CIAAW - Krypton isotopic/atomic-weight context
Questions to ask next about Krypton
A good element lesson should lead to the next useful question, not end after a list of facts.
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