For many years, chemists and other scientists thought that the inert or noble gases — helium, neon, argon, krypton, xenon, and radon — could not form chemical compounds and a valence of zero. In recounting how scientists did indeed create chemical compounds with the noble gases, Isaac Asimov, a chemist himself, wrote:
“The discovery of the noble-gas compounds came as a shock to some chemists and as a healthy object lesson to all. The universe is a very complicated place and there is very little of it we have penetrated. Even those portions of the universe with which we feel well acquainted can still hold surprises.”
Isaac Asimov, The Noble Gases, New York: Basic Books, 1966, p. 157.