Conventional scientific wisdom held that the noble gas elements could not form compounds because their electronic structure was extremely stable. For all except helium, the maximum capacity of the outer electron shell of the noble gas atom is eight electrons. For helium, that limit is just two electrons. These electron arrangements are especially stable, leaving the noble gases without a tendency to gain or loose electrons. This led chemists to think of them as totally unreactive.

A few chemists questioned the absolute inertness of the noble gases. Among those scientists were Walter Kossel in 1916 and Nobel-prize winning chemist Linus Pauling in 1933. They predicted that highly reactive atoms such as fluorine might form compounds with xenon, the heaviest of the noble elements and whose electrons, they observed, were not as tightly bound as those of the lighter gases.