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Key People:Lev Davidovich LandauSir wilhelm RamsayHeike Kamerlingh OnnesSir Edward FranklandSir Joseph Norman Lockyer...(Show more)Related Topics:AirAlpha particleHelium IIHelium-3Helium-4...(Show more)

Helium (He), chemistry element, inert gas of group 18 (noble gases) that the periodic table. The second lightest aspect (only hydrogen is lighter), helium is a colourless, odourless, and tasteless gas the becomes fluid at −268.9 °C (−452 °F). The boiling and also freezing point out of helium are lower than those of any kind of other known substance. Helium is the only facet that can not be coagulation by enough cooling at common atmospheric pressure; the is vital to apply pressure the 25 settings at a temperature that 1 K (−272 °C, or −458 °F) to transform it to its solid form.

Element Propertiesatomic numberatomic weightmelting pointboiling pointdensity (1 atm, 0 °C)oxidation stateelectron configuration
−268.9 °C (−452 °F)
0.1785 gram/litre


Helium was uncovered in the gaseous atmosphere surrounding the sunlight by the French astronomer Pierre Janssen, that detected a glowing yellow line in the spectrum that the solar chromosphere throughout an eclipse in 1868; this heat was originally assumed to stand for the aspect sodium. That very same year the English astronomer Joseph Norman Lockyer it was observed a yellow line in the solar spectrum that did no correspond to the known D1 and D2 currently of sodium, and so he named it the D3 line. Lockyer concluded the the D3 line was resulted in by an element in the sunlight that was unknown top top Earth; he and also the chemist Edward Frankland provided the Greek word for sun, hēlios, in naming the element. The brothers chemist teacher William Ramsay uncovered the presence of helium on planet in 1895. Ramsay obtained a sample that the uranium-bearing mineral cleveite, and, upon investigating the gas produced by heating the sample, he found that a distinct bright yellow line in its spectrum matched the of the D3 heat observed in the spectrum of the Sun; the new element the helium was hence conclusively identified. In 1903 Ramsay and Frederick Soddy further determined that helium is a product of the spontaneous disintegration of radiation substances.


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Abundance and isotopes

Helium constitutes about 23 percent the the mass of the universe and also is thus 2nd in abundance come hydrogen in the cosmos. Helium is focused in stars, where it is synthesized native hydrogen by atom fusion. Back helium wake up in Earth’s atmosphere only come the degree of 1 part in 200,000 (0.0005 percent) and small amounts occur in radioactive minerals, meteoric iron, and mineral springs, great volumes that helium are uncovered as a ingredient (up to 7.6 percent) in herbal gases in the United states (especially in Texas, new Mexico, Kansas, Oklahoma, Arizona, and Utah). Smaller supplies have actually been discovered in Algeria, Australia, Poland, Qatar, and Russia. Plain air contains around 5 parts per million that helium, and Earth’s tardy is only about 8 parts per billion.

The nucleus of every helium atom contains two protons, but, as is the situation with all elements, isotopes of helium exist. The well-known isotopes the helium contain native one to 6 neutrons, so their mass numbers variety from three to eight. The these 6 isotopes, only those v mass numbers of three (helium-3, or 3He) and also four (helium-4, or 4He) are stable; every the others room radioactive, decaying really rapidly right into other substances. The helium the is existing on earth is not a primordial component yet has been generated by radiation decay. Alpha particles, ejected indigenous the nuclei of heavier radioactive substances, are nuclei that the isotope helium-4. Helium does not accumulate in huge quantities in the atmosphere due to the fact that Earth’s heaviness is not enough to prevent its steady escape into space. The map of the isotope helium-3 on earth is attributable come the negative beta degeneration of the rarely hydrogen-3 isotope (tritium). Helium-4 is by much the many plentiful that the stable isotopes: helium-4 atom outnumber those that helium-3 around 700,000:1 in atmospheric helium and about 7,000,000:1 in specific helium-bearing minerals.


Helium-4 is distinctive in having two fluid forms. The common liquid form is dubbed helium I and also exists at temperature from that is boiling point of 4.21 K (−268.9 °C) down to around 2.18 K (−271 °C). Below 2.18 K, thermal conductivity the helium-4 becomes more than 1,000 times greater than that of copper. This liquid type is dubbed helium II to distinguish it from normal liquid helium I. Helium II exhibits the property dubbed superfluidity: that viscosity, or resistance come flow, is for this reason low the it has actually not to be measured. This liquid spreads in a thin film end the surface of any substance that touches, and also this film flows there is no friction even against the pressure of gravity. By contrast, the less plentiful helium-3 creates three distinguishable fluid phases of i m sorry two room superfluids. Superfluidity in helium-4 was uncovered by the Russian physicist Pyotr Leonidovich Kapitsa in the mid-1930s, and the exact same phenomenon in helium-3 was very first observed by Douglas D. Osheroff, David M. Lee, and Robert C. Richardson that the United states in 1972.


phase chart of helium-3
The step diagram of helium-3 shows which states of the isotope are stable.
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A fluid mixture that the two isotopes helium-3 and helium-4 off at temperatures below about 0.8 K (−272.4 °C, or −458.2 °F) into two layers. One class is virtually pure helium-3; the various other is greatly helium-4 yet retains around 6 percent helium-3 also at the shortest temperatures achieved. The dissolution of helium-3 in helium-4 is accompanied by a cooling effect that has been provided in the building of cryostats (devices for production of really low temperatures) that deserve to attain—and preserve for days—temperatures together low together 0.01 K (−273.14 °C, or −459.65 °F).

Production and uses

Helium gas (98.2 percent pure) is secluded from organic gas through liquefying the other materials at low temperatures and under high pressures. Adsorption of various other gases on cooled, triggered charcoal returns 99.995 percent pure helium. Some helium is gave from liquefaction of wait on a big scale; the quantity of helium obtainable native 1,000 tons (900 metric tons) of waiting is around 112 cubic feet (3.17 cubic metres), as measured at room temperature and also at common atmospheric pressure.

Helium is provided as one inert-gas environment for welding metals such as aluminum; in rocket propulsion (to pressurize fuel tanks, specifically those for liquid hydrogen, because only helium is still a gas at liquid-hydrogen temperature); in meteorology (as a lifting gas because that instrument-carrying balloons); in cryogenics (as a coolant because liquid helium is the coldest substance); and also in high-pressure breathing operations (mixed with oxygen, as in scuba diving and also caisson work, especially due to the fact that of its low solubility in the bloodstream). Meteorites and rocks have been analyzed for helium content as a way of dating.

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