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Key People:Lev Davidovich LandauSir William RamsayHeike Kamerlingh OnnesSir Edward FranklandSir Joseph Norguy Lockyer...(Sexactly how more)Related Topics:AirAlpha particleHelium IIHelium-3Helium-4...(Show more)
Helium (He), chemical aspect, inert gas of Group 18 (noble gases) of the routine table. The second lightest element (just hydrogen is lighter), helium is a colourmuch less, odourless, and tasteless gas that becomes liquid at −268.9 °C (−452 °F). The boiling and freezing points of helium are reduced than those of any type of other recognized substance. Helium is the only aspect that cannot be solidified by enough cooling at normal atmospheric pressure; it is important to apply pressure of 25 environments at a temperature of 1 K (−272 °C, or −458 °F) to transform it to its solid develop.
|−268.9 °C (−452 °F)|
Helium was found in the gaseous atmosphere surrounding the Sun by the French astronomer Pierre Janssen, that detected a bright yellow line in the spectrum of the solar chromosphere during an eclipse in 1868; this line was initially assumed to recurrent the element sodium. That same year the English astronomer Joseph Norman Lockyer observed a yellow line in the solar spectrum that did not correspond to the known D1 and D2 lines of sodium, and also so he called it the D3 line. Lockyer concluded that the D3 line was led to by an element in the Sun that was unknown on Earth; he and the chemist Edward Frankland provided the Greek word for sunlight, hēlios, in naming the aspect. The British chemist Sir William Ramsay discovered the visibility of helium on Earth in 1895. Ramsay obtained a sample of the uranium-bearing mineral cleveite, and also, upon investigating the gas developed by heating the sample, he discovered that a distinct bbest yellow line in its spectrum matched that of the D3 line oboffered in the spectrum of the Sun; the new facet of helium was therefore conclusively figured out. In 1903 Ramsay and also Frederick Soddy even more determined that helium is a product of the spontaneous fragmentation of radioactive substances.
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Abundance and also isotopes
Helium constitutes around 23 percent of the mass of the universe and is hence second in abundance to hydrogen in the cosmos. Helium is focused in stars, wright here it is synthesized from hydrogen by nuclear fusion. Although helium occurs in Earth’s atmosphere just to the extent of 1 component in 200,000 (0.0005 percent) and tiny quantities happen in radioenergetic minerals, meteoric iron, and mineral springs, excellent quantities of helium are found as a component (up to 7.6 percent) in herbal gases in the United States (specifically in Texas, New Mexico, Kansas, Oklahoma, Arizona, and also Utah). Smaller offers have been uncovered in Algeria, Australia, Poland, Qatar, and Russia. Ordinary air consists of about 5 components per million of helium, and also Earth’s crust is just around 8 components per billion.
The nucleus of eextremely helium atom has two proloads, however, as is the instance with all aspects, isotopes of helium exist. The known isotopes of helium contain from one to 6 neutrons, so their mass numbers variety from three to eight. Of these 6 isotopes, only those via mass numbers of three (helium-3, or 3He) and four (helium-4, or 4He) are stable; all the others are radioactive, decaying very rapidly into various other substances. The helium that is existing on Earth is not a primordial component yet has been created by radioenergetic decay. Alpha pshort articles, ejected from the nuclei of heavier radioactive substances, are nuclei of the isotope helium-4. Helium does not accumulate in big quantities in the setting because Earth’s gravity is not enough to prevent its steady escape into area. The trace of the isotope helium-3 on Earth is attributable to the negative beta degeneration of the rare hydrogen-3 isotope (tritium). Helium-4 is by much the most plentiful of the steady isotopes: helium-4 atoms outnumber those of helium-3 around 700,000:1 in atmospheric helium and also about 7,000,000:1 in certain helium-bearing minerals.
Helium-4 is distinctive in having 2 liquid develops. The normal liquid form is referred to as helium I and exists at temperatures from its boiling allude of 4.21 K (−268.9 °C) dvery own to about 2.18 K (−271 °C). Below 2.18 K, thermal conductivity of helium-4 becomes even more than 1,000 times better than that of copper. This liquid form is referred to as helium II to distinguish it from normal liquid helium I. Helium II exhibits the building called superfluidity: its viscosity, or resistance to circulation, is so low that it has not been measured. This liquid spreads in a thin film over the surchallenge of any substance it touches, and also this film flows without friction also versus the pressure of gravity. By contrast, the less numerous helium-3 forms 3 distinguishable liquid phases of which two are superfluids. Superfluidity in helium-4 was found by the Russian physicist Pyotr Leonidovich Kapitsa in the mid-1930s, and the very same phenomenon in helium-3 was initially oboffered by Douglas D. Osheroff, David M. Lee, and also Robert C. Richardchild of the USA in 1972.
phase diagram of helium-3
The phase diagram of helium-3 mirrors which says of the isotope are secure.
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A liquid mixture of the two isotopes helium-3 and helium-4 separates at temperatures listed below around 0.8 K (−272.4 °C, or −458.2 °F) into 2 layers. One layer is almost pure helium-3; the other is mainly helium-4 however retains around 6 percent helium-3 also at the lowest temperatures completed. The dissolution of helium-3 in helium-4 is accompanied by a cooling impact that has actually been supplied in the building of cryostats (gadgets for production of exceptionally low temperatures) that deserve to attain—and keep for days—temperatures as low as 0.01 K (−273.14 °C, or −459.65 °F).
Production and uses
Helium gas (98.2 percent pure) is isolated from natural gas by liquefying the various other components at low temperatures and also under high pressures. Adsorption of various other gases on cooled, triggered charcoal yields 99.995 percent pure helium. Some helium is provided from liquefaction of air on a huge scale; the amount of helium obtainable from 1,000 lots (900 metric tons) of air is around 112 cubic feet (3.17 cubic metres), as measured at room temperature and also at normal atmospheric pressure.
Helium is offered as an inert-gas setting for welding steels such as aluminum; in rocket propulsion (to pressurize fuel tanks, especially those for liquid hydrogen, because only helium is still a gas at liquid-hydrogen temperature); in meteorology (as a lifting gas for instrument-transporting balloons); in cryogenics (as a coolant bereason liquid helium is the coldest substance); and also in high-push breapoint operations (mixed through oxygen, as in scuba diving and caiskid work-related, particularly bereason of its low solubility in the bloodstream). Meteorites and also rocks have been analyzed for helium content as a way of dating.
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