Krypton (Kr) is a chemical element (atomic number 36) found in trace amounts in the Earth’s atmosphere. At standard temperature and pressure, krypton exists as a colorless, odorless, and tasteless gas. The terms malleable, ductile, and brittle are engineering descriptors that apply exclusively to solid materials with a well-defined crystalline structure. Since krypton is a gas, these properties do not describe its behavior under normal conditions.
Why Malleability and Brittleness Do Not Apply
Krypton is a member of Group 18 (noble gases), which dictates its chemical and physical nature. Noble gas atoms possess a full outer valence electron shell, giving them extreme stability and a lack of chemical reactivity under ordinary conditions. This complete shell means krypton exists as a monatomic gas, where individual atoms are not chemically bonded.
Malleable and ductile describe a material’s ability to undergo plastic deformation without fracturing. Malleability is the capacity to be hammered into thin sheets, while ductility is the ability to be drawn into a wire. These characteristics are hallmarks of metals, which feature delocalized electrons that allow atoms to slide past one another without breaking metallic bonds.
Brittleness, conversely, describes a material that fractures with little or no plastic deformation when subjected to stress. This property is common in materials with strong, rigid, localized bonds, such as ceramics or certain types of solids that shatter easily. Since krypton’s atoms are not held together by metallic, ionic, or strong covalent bonds, the concepts of being permanently shaped or shattering under force do not apply. Krypton’s atoms are entirely free-moving, meaning the gas simply expands to fill any container and cannot be deformed or fractured.
The Actual Physical Properties of Krypton
The measurable physical properties of krypton relate to its phase changes from gas to liquid and then to solid. Krypton remains a gas until cooled to extremely low temperatures, reflecting the weak forces holding its atoms together. It has a boiling point of approximately -153.4°C and a melting point of about -157.4°C.
When krypton is cooled below its melting point, it transitions into a solid state. This white, crystalline substance forms a face-centered cubic structure, which is typical for solidified noble gases. The forces that hold this solid structure together are weak intermolecular forces known as London dispersion forces, which are the only attractive forces between the non-polar krypton atoms.
Because the bonding is based on these weak, temporary forces, solid krypton is categorized as a molecular solid. If this cryogenic solid were to be subjected to mechanical stress, the weak bonds would break immediately, causing the material to shatter. Therefore, while krypton is a gas at its natural state, its extremely cold solid form would be highly brittle and certainly not malleable or ductile.
Practical Applications of Krypton
Despite its rarity, krypton’s unique properties make it valuable for several high-performance industrial applications. The gas is commonly used as a filler in certain types of lighting, such as high-speed photography flash lamps and specialized halogen lamps. Krypton allows for higher operating temperatures and pressures, leading to brighter, more energy-efficient bulbs than those filled with argon, and helps reduce filament evaporation.
Krypton is also employed in the manufacturing of energy-efficient, multi-paned windows. Because krypton is significantly denser than air, sealing it between the glass panes provides superior thermal and sound insulation, which is particularly useful in extreme climates.
Furthermore, the element is a component in specific types of lasers, such as the krypton fluoride (KrF) excimer laser, which is used in semiconductor production and nuclear fusion research. Krypton has also played a historical role in metrology; from 1960 to 1983, the official definition of the meter was based on the specific wavelength of the orange-red spectral line emitted by a krypton-86 isotope lamp.