Superfluidity in helium-4 was discovered by the Russian physicist Pyotr Leonidovich Kapitsa in the mid-1930s, and the same phenomenon in helium-3 was first observed by Douglas D. This liquid spreads in a thin film over the surface of any substance it touches, and this film flows without friction even against the force of gravity.īy contrast, the less plentiful helium-3 forms three distinguishable liquid phases of which two are superfluids. Helium II exhibits the property called superfluidity: its viscosity, or resistance to flow, is so low that it has not been measured. This liquid form is called helium II to distinguish it from normal liquid helium I. The normal liquid form is called helium I and exists at temperatures from Helium I's boiling point of 4.21 K (−268.9 ☌) down to about 2.18 K (−271 ☌).īelow 2.18 K, thermal conductivity of helium-4 becomes more than 1,000 times greater than that of copper. Helium-4 is unique in having two liquid forms. Helium was detected in the sun by its spectral lines many years before it was found on Earth.Ī colourless, odourless gas that is totally unreactive.īelow Helium's boiling point of 4.22 K (−268.93 ☌ −452.07 ☏) and above the lambda point of 2.1768 K (−270.9732 ☌ −455.7518 ☏), the isotope helium-4 exists in a normal colorless liquid state, called helium I. Helium gets Helium's name from ‘helios’, the Greek word for the sun. However, some studies suggest that helium produced deep in the earth by radioactive decay can collect in natural gas reserves in larger than expected quantities, in some cases, having been released by volcanic activity. Helium's supply is thought to be rapidly diminishing. Terrestrial helium is a non-renewable resource because once released into the atmosphere, Helium promptly escapes into space. This radiogenic helium is trapped with natural gas in concentrations as great as 7% by volume, from which Helium is extracted commercially by a low-temperature separation process called fractional distillation. Most terrestrial helium present today is created by the natural radioactive decay of heavy radioactive elements (thorium and uranium, although there are other examples), as the alpha particles emitted by such decays consist of helium-4 nuclei. On Earth, Helium is relatively rare-5.2 ppm by volume in the atmosphere. In 1903, large reserves of helium were found in natural gas fields in parts of the United States, by far the largest supplier of the gas today. The formal discovery of the element was made in 1895 by chemists Sir William Ramsay, Per Teodor Cleve, and Nils Abraham Langlet, who found helium emanating from the uranium ore, cleveite, which is now not regarded as a separate mineral species, but as a variety of uraninite. Lockyer was the first to propose that the line was due to a new element, which he named. Janssen recorded the helium spectral line during the solar eclipse of 1868, while Lockyer observed Helium from Britain. Janssen is often jointly credited with detecting the element, along with Norman Lockyer. Pogson, and Lieutenant John Herschel, and was subsequently confirmed by French astronomer Jules Janssen. Helium was first detected as an unknown, yellow spectral line signature in sunlight during a solar eclipse in 1868 by Georges Rayet, Captain C. Large amounts of new helium are created by nuclear fusion of hydrogen in stars. Most helium in the universe is helium-4, the vast majority of which was formed during the Big Bang. This helium-4 binding energy also accounts for why Helium is a product of both nuclear fusion and radioactive decay. Helium's abundance is similar to this in both the Sun and in Jupiter, due to the very high nuclear binding energy (per nucleon) of helium-4, with respect to the next three elements after helium. Helium is present at about 24% of the total elemental mass, which is more than 12 times the mass of all the heavier elements combined. Helium is the second lightest and second most abundant element in the observable universe (hydrogen is the lightest and most abundant). Helium's boiling and melting point are the lowest among all the elements. Helium is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. Helium (from Greek: ἥλιος, romanized: helios, lit. 'sun') is a chemical element with the symbol He and atomic number 2.
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