Nepedia
Back to Discover
Advanced Reader
⚛️

Krypton

physical science Maturity 11-13 Next article →

Krypton is a chemical element with the symbol Kr and the atomic number 36. It belongs to a group of elements known as the noble gases.

KrTube
KrTube

These gases are characterized by being colorless and odorless. Krypton is also chemically inert, which means it is highly unreactive with other substances. It exists in our atmosphere in trace amounts, roughly 1 part per million. Because it is so stable, it is used in many specialized technological applications. It can act as a light source, a laser medium, or even a propellant in space.

One fascinating way krypton works is through the creation of an exciplex laser.

In a krypton fluoride laser, the krypton gas absorbs energy from a specific source. This energy causes the krypton to react with fluorine gas. This reaction produces an exciplex, which is a temporary complex in an excited energy state. This complex then undergoes spontaneous or stimulated emission. This process reduces its energy state to a metastable ground state. The complex quickly dissociates into unbound atoms. This release of energy radiates at 248 nm, which is near the ultraviolet portion of the spectrum.

Krypton exists in several different forms, known as isotopes. Naturally occurring krypton in Earth's atmosphere is composed of five stable isotopes. There is also an isotope called 78Kr, which has an incredibly long half-life of 9.2×10^21 years. Because this decay takes so long, it is considered stable. Scientists also study unstable isotopes like 85Kr, which is produced by the fission of uranium and plutonium. This isotope has a half-life of 10.76 years. Another isotope, 81Kr, is produced by cosmic ray irradiation. It has a half-life of 230,000 years and helps scientists date groundwater that is between 50,000 and 800,000 years old.

The history of krypton is tied to the discovery of the noble gases.

William Ramsay working
William Ramsay working

In 1898, two chemists in Britain discovered the element. These were William Ramsay, a Scottish chemist, and Morris Travers, an English chemist. They found krypton by examining the residue left after evaporating nearly all the components of liquid air. Just a few weeks later, these same workers discovered neon using a similar method. For his work in discovering this series of noble gases, William Ramsay was awarded the 1904 Nobel Prize in Chemistry.

Krypton has played a vital role in how humans define measurements. From 1960 to 1983, the official definition of the meter was based on krypton-86.

KrTube
KrTube

Specifically, the meter was defined as 1,650,763.73 wavelengths of light emitted in a vacuum. This light corresponds to a specific transition between the 2p10 and 5d5 energy levels. This definition replaced the 1889 international prototype meter, which was a physical metal bar located in Sèvres. The use of krypton-86 was preferred because of its high power and the ease of operating krypton discharge tubes. This standard was eventually replaced in 1983 by a definition based on the speed of light.

There are many surprising ways krypton is used in modern science and industry.

In particle physics, liquid krypton is used to build electromagnetic calorimeters. For example, the NA48 experiment at CERN uses about 27 tonnes of liquid krypton. It is chosen because it has a small Molière radius of 4.7 cm, which allows for excellent spatial resolution. In the field of space exploration, SpaceX Starlink uses krypton as a propellant for its electric propulsion systems. Even in medicine, the isotope krypton-81m is inhaled by patients to perform lung ventilation and perfusion scans using a gamma camera.

Krypton also has unique physical and chemical properties that scientists study under extreme conditions. When solid, krypton has a face-centered cubic crystal structure.

Scientists have even grown krypton hydride crystals, known as Kr(H2)4, at pressures above 5 GPa. These crystals feature krypton octahedra surrounded by hydrogen molecules. While krypton is mostly unreactive, it can form compounds with fluorine under extreme conditions. It can also form polyatomic ions like the kryptonium ion, KrH+. These specialized chemical behaviors help researchers understand the fundamental rules of how atoms interact.

681 words

Where will your curiosity go next?

Keep exploring at your chosen reading level.

🖼️ Images & Media (5)
File:William Ramsay working.jpg
William Ramsay working.jpg
File:Krypton hydride crystal.jpg
Krypton hydride crystal.jpg
File:Krypton hydride structure.png
Krypton hydride structure.png
File:KrTube.jpg
KrTube.jpg
File:The Meyer-Overton correlation.png
The Meyer-Overton correlation.png
More to explore

✨ What else?

Related topics you might enjoy

🔬 Go deeper

More advanced topics to explore

🪜 Step back

Simpler topics to build understanding

What is Nepedia?

A free, ad-free encyclopedia for children. Every article is written at five reading levels, so the same page works for a five-year-old and a fifteen-year-old — use the level switcher above to see this one change. No account needed to read.