A Broken Rule: Chemical Reactions of the Noble Gases

Home , Chemically inert, Helium, Hexafluoride, Krypton, Krypton difluoride, Neil Bartlett (chemist)

A Broken Rule: Chemical Reactions of the Noble Gases Discovery of “Inert” Gases Noble Gases React they are kept away from water or The noble gas elements (helium, The belief that noble gases were other compounds with which they neon, argon, krypton, xenon, and inert was shattered in 1962 when react. However, other noble gas com- radon) were identified in the eigh- the first compound containing a pounds that were discovered during teenth and nineteenth centuries. noble gas element was prepared by the 1960s are not stable. Xenon tri- However, the ability of noble gases to Neil Bartlett, then a professor at the oxide, which forms when xenon combine with other elements was dis- University of British Columbia. He tetrafluoride reacts with water, is covered less than 50 years ago when was studying the chemical reaction highly unstable and explosive. the first noble gas compounds were between molecular oxygen (O2) and Chemists are still actively studying produced. These discoveries illustrate platinum hexafluoride (PtF6), which the reactivity of the noble gases. that chemistry is a constantly chang- is an extremely strong oxidant. (An Recently, an argon compound was ing science. oxidant is a compound that has the identified at very low temperatures. The noble gases were long known ability to take electrons away from However, there are still no known as inert gases because of their partic- other compounds.) Realizing that stable compounds of helium or neon. ularly stable and unreactive struc- xenon and oxygen gas have similar Today the noble gas elements have tures. The first clues to their existence abilities for giving up electrons (ion- many important applications, such as actually arose from their lack of reac- ization potentials), Bartlett hoped neon lights and gas lasers. In con- tivity. English scientist Henry that PtF6 might also react with trast, the noble gas compounds have Cavendish identified a small compo- xenon. He placed colorless xenon yet to be developed to solve any spe- nent of air that did not undergo cer- gas in one tube that was separated cific technological problems. However, tain chemical reactions common for by a seal from a second tube con- the fluorine atoms in xenon hexafluo- the elements thought to be present taining the red PtF6.When the seal ride and similar compounds will bond in air (oxygen, nitrogen, and hydro- was broken, the gases mixed, and a to organic molecules, which may be gen). However, the unreacted portion yellow solid formed. This solid was useful for drug preparation. was not identified as a new element xenon hexafluoroplatinate, the first until more than a century later when noble gas compound! Questions Lord Rayleigh and Sir William Ramsay 1. Because radon is a noble gas, it Noble Gas Compounds repeated Cavendish’s experiment is considered chemically inert. Bartlett’s amazing discovery that the using new analysis techniques. However, this element is often in “inert” gases were not completely Because of the noble gases’ history the news. Why is radon a safety inert caused great excitement. In less of inactivity, most chemists prior to the concern? than two years, other researchers 1960s believed that these gases were discovered that other noble gas 2. Given that XeF reacts with water not capable of forming compounds. 4 compounds, such as xenon tetrafluo- to form explosive XeO ,chemists This belief continues to influence our 3 ride (XeF ) and krypton difluoride would not handle it near water. understanding of chemistry. The reac- 4 (KrF ), could be prepared by reacting However, why would you still not tivity of atoms is still partly attributed 2 xenon or krypton with fluorine gas. want to work with it on the lab to the stability an atom has when the The simple compounds made of bench, even if there was appar- outer electron shell is completely xenon and fluorine are stable solids ently no water around? filled, as it is in the noble gases. at normal temperatures, as long as