36 Kr Krypton 83.798
Noble gas p-block Period 4 Group 18

Krypton

Kr · Element 36 · Noble gases

Named "hidden", used to define the metre, and briefly the fictional weakness of a superhero.

STATE AT 20°C Gas
ATOMIC MASS 83.798 u
ELECTRON CONFIGURATION [Ar] 3d¹⁰ 4s² 4p⁶

Structure

The krypton atom

Not a diagram of dots on rings — a Monte-Carlo sample of the actual probability density |ψ|² for each occupied subshell. Drag to rotate. Blue and violet mark opposite signs of the wavefunction, which is what makes bonding possible.

Orbital cloud

Measured values

Property sheet

Every bar shows where krypton sits among all 118 elements for that property.

Physical

Density 0.004 g/cm³ 7%
Melting point 115.8 K 6%
Boiling point 119.9 K 7%
Specific heat 0.248 J/g·K
Thermal conductivity 0.01 W/m·K 1%

Atomic

Atomic radius 116 pm 12%
Covalent radius 116 pm
Van der Waals radius 202 pm

Electronic

Electronegativity 3 96%
Ionisation energy 1350.8 kJ/mol 96%
Electron affinity 0 kJ/mol 0%

Occurrence

Abundance in crust 0.0001 mg/kg 30%

Identity

SymbolKr
Atomic number36
Atomic mass83.798 u
CategoryNoble gas
Blockp
Crystal structureface-centered cubic
Oxidation states0, +2
Discovered1898
Discovered byRamsay & Travers

Sources: IUPAC 2021 standard atomic weights · CRC Handbook of Chemistry and Physics · NIST. Values marked ~ are predicted rather than measured.

Size, to scale

How big is a krypton atom?

Radius 116 pm — that is 0.116 nm, so about 4310 million of them side by side would span a millimetre.

Thermal range

Solid, liquid, gas — and when

Krypton is liquid over a 4 K window, from 116 K to 120 K.

Where it sits

Position in the table

Krypton sits in period 4, group 18. Everything in group 18 shares the same outer-electron count, which is why they behave so similarly.

OTHER NOBLE GASS

All noble gass

The story

What krypton is, and how we found it

Krypton is the brilliant noble gas that illuminates our world with stunning white light and helped redefine the meter. This colorless, odorless gas might share its name with Superman's home planet, but its real superpower is producing incredibly bright, energy-efficient lighting. Named after the Greek word "kryptos" meaning hidden, krypton lived up to its name by hiding in plain sight in our atmosphere for over a century. Discovered in 1898 by British chemists Sir William Ramsay and Morris Travers at University College London, krypton was found through the painstaking fractional distillation of liquid air. They had already discovered argon and helium, and suspected more noble gases existed. When they found krypton, they were amazed by its brilliant white light when electrified, leading Ramsay to exclaim that it produced "the most beautiful light in the world." What makes krypton absolutely fascinating is its role in precision science. From 1960 to 1983, the meter was officially defined as exactly 1,650,763.73 wavelengths of orange-red light emitted by krypton-86 atoms. This made krypton the foundation of the international measurement system. Even though the meter is now defined by the speed of light, krypton's incredibly pure spectral lines made it perfect for this crucial role. Krypton gas produces stunning lighting effects. When electricity passes through krypton, it emits brilliant white light that's much brighter and whiter than other noble gases. High-end flashlights, airport runway lights, and professional photography equipment use krypton bulbs because they produce light closest to natural sunlight. Here's something mind-blowing: krypton is produced inside nuclear reactors as uranium splits apart. Krypton-85, a radioactive isotope, is used to detect leaks in sealed containers and as a tracer gas. Scientists can even detect secret nuclear weapons tests by measuring krypton-85 in the atmosphere.

The discovery of krypton

The Hidden Gas

William Ramsay and Morris Travers discovered krypton in 1898 through systematic fractional distillation of liquid air. They named it krypton from the Greek "kryptos" meaning hidden, reflecting the difficulty of its isolation and detection.

Applications

What krypton is used for

Krypton: The Lighting Specialist

Krypton's unique spectral properties create brilliant white light for photography, automotive, and architectural applications, while its chemical inertness enables specialized scientific and industrial uses requiring ultra-pure environments.

High-Performance Lighting

Krypton arc lamps produce intense, color-balanced white light essential for professional photography, film production, and scientific applications. Automotive headlights use krypton fill gas to increase bulb efficiency and extend service life compared to standard halogen systems.

Window Insulation

Krypton-filled windows provide superior thermal insulation due to krypton's low thermal conductivity, enabling ultra-high-performance glazing systems for energy-efficient buildings and specialized applications requiring minimal heat transfer.

Laser Technology

Krypton fluoride (KrF) excimer lasers operating at 248 nm wavelength enable semiconductor photolithography for advanced microprocessor manufacturing, creating circuit features smaller than 100 nanometers essential for modern electronics.

Krypton: Specialized Excellence

  • Professional Lighting
    • Photography and film studio lighting
    • Automotive high-performance headlights
    • Airport runway and navigation lighting
    • Architectural and display lighting
  • Energy Efficiency
    • High-performance window insulation
    • Energy-efficient building glazing
    • Specialized thermal barrier applications
    • Cryogenic insulation systems
  • Scientific Applications
    • Semiconductor manufacturing lasers
    • Research laser systems
    • Gas chromatography carrier gas
    • Particle detector fill gas

Where it comes from

Natural occurrence

0.0001 mg/kg of Earth's crust · more abundant than 30% of elements

Krypton: Atmospheric Rarity

Krypton exists primarily in Earth's atmosphere at 1.14 parts per million, formed through radioactive decay of primordial isotopes and cosmic ray interactions. Commercial krypton extraction requires processing millions of cubic meters of air through cryogenic distillation.

Handling

Safety

Krypton Safety: Inert but Asphyxiant

Krypton presents minimal chemical hazards due to its noble gas properties but can cause asphyxiation in confined spaces by displacing oxygen. Proper ventilation and oxygen monitoring prevent asphyxiation risks.

Safety Measures

Oxygen monitoring and adequate ventilation prevent asphyxiation hazards when using krypton in enclosed spaces. Standard inert gas handling procedures apply for storage and transportation.

Quick answers

Krypton: common questions

What is Krypton?

Krypton (symbol Kr) is element 36 on the periodic table, a noble gas in period 4, group 18. Named "hidden", used to define the metre, and briefly the fictional weakness of a superhero. At room temperature it is a gas.

What is the electron configuration of Krypton?

Krypton's ground-state electron configuration is [Ar] 3d¹⁰ 4s² 4p⁶, giving 4 occupied shells holding 2, 8, 18, 8 electrons respectively. Its outer shell holds 8 electrons, which is what sets its bonding behaviour.

What are the melting and boiling points of Krypton?

Krypton melts at 115.8 K (-157.4 °C) and boils at 119.9 K (-153.2 °C).

What is the atomic mass of Krypton?

The standard atomic weight of Krypton is 83.798 u. That is a weighted average across its naturally occurring isotopes, which is why it is rarely a whole number.

How dense is Krypton?

Krypton is a gas at room temperature; its density is about 3.733 g/L at 0 °C and 1 atm — roughly heavier than air.

What is the electronegativity of Krypton?

Krypton has a Pauling electronegativity of 3. The scale runs from 0.70 (francium, the least greedy for electrons) to 3.98 (fluorine, the most). A value this high means it tends to pull electrons away from almost anything it bonds with.

Who discovered Krypton, and when?

Krypton was discovered in 1898 by Ramsay & Travers. It is named after greek kryptos, "hidden".

How common is Krypton on Earth?

Krypton makes up about 1.00e-4 mg/kg of the Earth's crust — genuinely rare, which is why it is expensive.