INORGANIC CHEMISTRY A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z                    HOME ABOUT CATEGORIES SITE MAP COPYRIGHT ADVERTISE CONTACT entire Web this site helium (He) A colorless, odorless, inert gaseous element which is the second most abundant element in the universe after hydrogen. It is named after the Greek word for the Sun, helios, because it was discovered, by virtue of its spectral lines, in the Sun. Jules Janssen obtained the first evidence of helium during the solar eclipse of 1868 when he detected a new line in the solar spectrum. J. Norman Lockyer and Edward Frankland suggested the name helium for the new element. In 1895 William Ramsay discovered helium in the uranium mineral cleveite; it was independently discovered in cleveite by the Swedish chemists Cleve and Langlet at about the same time. In 1907, Ernest Rutherford and Thomas Royds demonstrated that alpha particles are helium nuclei. An ordinary helium atom consists of a nucleus of two protons and two neutrons surrounded by two electrons. Seven isotopes of helium are known. Liquid helium (He-4) exists in two forms: He-4I and He-4II, with a sharp transition point at 2.174K. He-4I (above this temperature) is a normal liquid, but He-4II (below it) is unlike any other known substance. Most of the helium in the universe was produced immediately after the Big Bang, although an additional contribution has come from hydrogen burning inside main sequence stars. It occurs commonly in stars and in the atmospheres of gas giants. See also elements, cosmic abundance. The helium content of Earth's atmosphere is about 1 part in 200,000. atomic number 2 relative atomic mass 4.0026 electron configuration 1s2 atomic radius 128 pm density 0.176 g/dm3 melting point -269.7 °C (-453.5 °F) boiling point -268.9 °C (-452.0 °F) Sources and uses of helium Helium is extracted from natural gas, all of which contains at least trace quantities of helium. Helium is used to inflate and provide lift for balloons, as an inert component of various artificial atmospheres (such as those used by divers), in gaseous laser media, as an inert gas shield for arc welding, as a protective gas in growing silicon and germanium crystals and producing titanium and zirconium, and as a superfluid in the form of helium II. Related category    • INORGANIC CHEMISTRY Source: Los Alamos National Laboratory Also on this site: Encyclopedia of Alternative Energy & Sustainable Living Encyclopedia of History Transport Concepts & Designs (partner site) BACK TO TOP