What Is Krypton?

Krypton is a chemical element with the symbol Kr and atomic number 36, classified as a noble gas in Group 18 of the periodic table. It is a colorless, odorless gas present only in trace amounts in Earth's atmosphere, named from the Greek word "kryptos," meaning "hidden," directly reflecting how difficult it was to detect and isolate compared to more abundant atmospheric gases.

Despite its name's reference to popular culture (Superman's fictional home planet Krypton was almost certainly inspired by the real element's exotic-sounding name), krypton itself has several genuine, practical scientific and industrial applications, particularly in specialized lighting and, historically, in defining international standards of measurement.

Krypton's electron configuration of [Ar] 3d¹⁰ 4s² 4p⁶ gives it a complete, fully satisfied outer shell, the defining trait of noble gases, leaving it with minimal natural tendency to participate in chemical bonding under normal conditions.

Physical & Chemical Properties

Krypton has an atomic mass of 83.798 u and a gas density of 0.003425 g/cm³, notably denser than air despite remaining a relatively light gas in absolute terms. It has a melting point of -157.4°C and a boiling point of -153.2°C.

As a noble gas, krypton is chemically inert under normal conditions, forming essentially no stable compounds in ordinary chemistry, though under extreme laboratory conditions a small number of unstable krypton compounds have been synthesized, similar to research done with its larger relative xenon. Krypton produces a characteristic, distinctively colored glow when electrically excited, a property exploited in specialized lighting and certain laser applications, including some used in particular ophthalmologic medical procedures.

Electron Configuration Explained

Krypton's electron configuration is [Ar] 3d¹⁰ 4s² 4p⁶, meaning it has a complete argon-based core plus a fully filled 3d subshell and a completely satisfied set of 4s and 4p electrons.

This complete outer shell configuration is the standard noble gas pattern, providing krypton with substantial chemical stability under normal conditions, though somewhat less absolute than in the smaller, lighter noble gases like helium and neon. Krypton's position between argon and xenon in the noble gas group reflects this trend — slightly more reactive than argon, but considerably less prone to compound formation than the larger, more loosely-bound xenon positioned further down the same group.

Like other noble gases, krypton's filled outer shell is frequently used as a convenient shorthand reference point for describing the more complex electron configurations of heavier elements positioned later in the periodic table.

History & Discovery

Krypton was discovered in 1898 by Scottish chemist William Ramsay and English chemist Morris Travers, identified as part of their systematic study of the residue remaining after liquid air was allowed to evaporate — the same productive research period that also yielded the discovery of neon and xenon in rapid succession.

Krypton gained an unusual additional layer of cultural significance decades after its scientific discovery, when comic book creators chose "Krypton" as the name for Superman's fictional home planet, likely drawn to the element's exotic-sounding name even though the fictional planet has no particular scientific connection to the actual chemical element beyond sharing its evocative name.

What Is Krypton Used For?

Krypton's distinctive light-producing properties drive several specialized applications:

  • Fluorescent and specialty lamps: Krypton gas is used in certain energy-efficient fluorescent lighting and other specialized lamp applications, exploiting its characteristic emission properties when electrically excited.
  • Lasers: Krypton is used in certain laser technologies, including some applications in scientific research and specialized medical procedures.
  • Photography flash: Krypton has historically been used in certain high-intensity photographic flash applications.
  • Window insulation: Like argon, krypton gas can be used to fill the space between window panes in certain high-performance, energy-efficient window designs, taking advantage of its low thermal conductivity.
  • Historical length standard: From 1960 to 1983, the international meter was officially defined based on the wavelength of light emitted by krypton-86, before later being redefined using the speed of light.

Common Krypton Compounds

True to its identity as a noble gas, krypton forms essentially no stable compounds under normal conditions. A small number of unstable krypton compounds, particularly krypton difluoride, have been synthesized under extreme laboratory conditions, similar to research conducted with xenon, but these compounds have no practical applications and exist only briefly under tightly controlled experimental circumstances. For all practical purposes, krypton exists in nature and in its various applications exclusively as the free, uncombined element.

Fun Facts About Krypton

  • From 1960 until 1983, the official international definition of the meter was based on the wavelength of light emitted by krypton-86 atoms, before the standard was later redefined using the speed of light for even greater precision.
  • The name "Krypton," chosen for Superman's fictional home planet, almost certainly drew inspiration from the real element's exotic, mysterious-sounding Greek-derived name, though the fictional planet shares no actual scientific connection to the real chemical element.
  • Krypton makes up only a tiny fraction of Earth's atmosphere, roughly one part per million, making it considerably rarer than other atmospheric noble gases like argon.
  • Krypton was discovered as part of the same prolific research effort by William Ramsay and Morris Travers that also identified both neon and xenon within a relatively short span of time.

Frequently Asked Questions

Is krypton related to Superman?
Only in name — Superman's fictional home planet Krypton was almost certainly named after the real chemical element due to its exotic-sounding name, but there's no actual scientific connection between the fictional planet and the real, much more mundane noble gas.

What is krypton's atomic number?
Krypton has atomic number 36, meaning each krypton atom contains 36 protons in its nucleus.

Was the meter once defined using krypton?
Yes, from 1960 to 1983, the international meter was officially defined based on the wavelength of light emitted by krypton-86 atoms, before later being redefined using the speed of light for improved precision.

Is krypton found naturally on Earth?
Yes, krypton exists in trace amounts in Earth's atmosphere, making up roughly one part per million of the air, making it considerably rarer than other noble gases like argon.