Rare Gases

Helium was the first of the rare gases to be discovered. In fact, its discovery is unique among the elements since it is the only element to be first identified in another part of the solar system before being discovered on Earth. In 1868 Pierre Janssen (1824-1907), a French astronomer, was observing a total solar eclipse from India. Janssen used an instrument called a spectroscope to analyze the sunlight. The spectroscope broke the sunlight into lines which were characteristic of the elements emitting the light. He saw a previously unobserved line in the solar spectrum which indicated the presence of a new element that Janssen named helium after the Greek word helios, meaning sun. A quarter of a century later, William Ramsay (1852-1916) studied gases emitted from radioactive uranium ores. With help from two British experts on spectroscopy, William Crooks (1832-1919) and Norman Lockyer (1836-1920), the presence of helium in earth-bound minerals was confirmed. Shortly thereafter, helium was also detected as a minor component in the earth's atmosphere.

The discovery of the remaining rare gases is credited to two men, Ramsay and Lord Rayleigh (1842-1919). Beginning in 1893, Rayleigh observed discrepancies in the density of nitrogen obtained from different sources. Nitrogen obtained from the air (after removal of oxygen, carbon dioxide, and water vapor) always had a slightly higher density than when prepared from a chemical reaction (such as heating certain nitrogen-containing compounds). Ramsay eventually concluded that the nitrogen obtained from chemical reactions was pure, but nitrogen extracted from the air contained small amounts of an unknown gas which accounted for the density discrepancy. Eventually it was realized that there were several new gases in the air. The method used to isolate these new gaseous elements involved liquefying air (by subjecting it to high pressure and low temperature) and allowing the various gases to boil off at different temperatures. The names given to the new elements were derived from Greek words that reflected the difficultly in isolating them: Ne, neos (new); Ar, argos (inactive); Kr, kryptos (hidden); Xe, xenon (stranger). Radon, which is radioactive, was first detected as a gas released from radium, and subsequently identified in air. Ramsay and Rayleigh received Nobel Prizes in 1904 for their scientific contributions in discovering and characterizing the rare gases.