Noble Gases, or Inert Gases, a group of six chemical elements all of which are highly resistant to chemical action; that is, chemically inert. (In chemistry, the terms noble and inert are synonymous.) These elements are (in order of increasing atomic weight) helium, neon, argon, krypton, xenon, and radon. All six are gases at normal temperatures and pressures. They all occur naturally in the earth's atmosphere, and helium is also found in natural-gas wells.

Discovery of the Noble Gases

In 1775 the English scientist Henry Cavendish analyzed a sample of air. He found that after all the substances then known to be in air were accounted for, a tiny part of the original sample remained. This discovery went unexplained until 1894, when Lord Rayleigh and Sir William Ramsay discovered that a hitherto unknown element, argon, constitutes most of the remainder. By 1901 the five other noble gases had been isolated and identified by Ramsey and other scientists.

At the time of their discovery, all of the noble gases were believed to be extremely rare, and therefore they were often referred to as rare gases. This term is still used occasionally, even though argon constitutes almost 1 per cent of the earth's atmosphere and helium occurs in concentrations of 2 per cent or more in many natural-gas wells.

Noble-Gas Compounds

The noble gases, all of which have their outermost electron shells filled, constitute a separate group in the Periodic Table of the elements. Because of their inertness, the noble gases form no chemical compounds in nature. In 1962 Neil Bartlett, a British chemist, formed the first noble-gas compound in experiments conducted at the University of British Columbia. The compound was xenon hexafluoroplatinate, an orange-yellow solid composed of xenon, fluorine, and platinum. Other xenon compounds, and compounds containing krypton and radon, were subsequently formed.