Krypton (Kr) is a colorless, odorless, and chemically inert gas that exists in trace amounts within the Earth’s atmosphere. It is a member of the noble gas family, Group 18 on the periodic table, characterized by its low reactivity with other elements. Though present at only about one part per million by volume in the air, the element holds a significant place in the history of chemistry.
The Search for Missing Noble Gases
The late 19th century saw a significant gap in the organization of the periodic table following the discovery of Argon in 1894. Argon’s lack of chemical reactivity suggested the existence of an entire family of elements that had been missed in previous analyses of atmospheric components. Scientists realized a new, unrepresented group was likely positioned between the highly reactive halogens and the alkali metals.
The search focused on finding other inert gases that were expected to be present in the air, but in much smaller quantities than the major constituents like nitrogen and oxygen. The properties of the known noble gases, Helium and Argon, provided clues for predicting the characteristics of their heavier counterparts. Researchers were motivated by the possibility of finding elements with atomic numbers 10, 36, 54, and 86, which would complete this new vertical group.
The Specific Location and Method of Discovery
The discovery of Krypton occurred in 1898 in the laboratory of Sir William Ramsay, with the assistance of his student, Morris Travers. The experimental work took place in London, England, at University College, where Ramsay held the Chair of Chemistry. Their method involved the technique of liquefying a large volume of atmospheric air and then systematically boiling off its components.
The process relied on fractional distillation, which separates substances based on their different boiling points. Air was first cooled until it turned into a liquid, primarily composed of liquid nitrogen, oxygen, and argon. As the liquid air was allowed to warm, the most volatile components, such as nitrogen and oxygen, boiled away at their respective low temperatures.
This left behind a minuscule, non-volatile residue that was significantly heavier than the bulk of the original sample. This residue contained the trace noble gases concentrated by the removal of the more abundant components. The scientists found that this remaining material yielded a gas heavier than Argon, which they immediately suspected was a new element. Krypton was officially discovered on May 30, 1898.
Naming the Element and Initial Confirmation
Upon isolating the new gas, Ramsay and Travers quickly proceeded to confirm its identity using spectroscopic analysis. When a high-voltage electric current was passed through the sample, the gas emitted a distinct light spectrum. This spectral signature was unique, featuring a series of bright lines that did not match any known element.
Specifically, the gas produced a characteristic set of vibrant green and yellow spectral lines, providing evidence of a new element. Following this confirmation, the element was given the name Krypton, which comes from the Greek word kryptos. This term translates to “the hidden one,” a fitting name considering how successfully the gas had remained concealed within the atmosphere.