Helium (He)
Helium (He) is a colorless, odorless gas and the second lightest element on the periodic table, with an atomic number of 2. It is primarily known for its remarkable properties as a cryogenic coolant, which enables cooling to extremely low temperatures, and is used in applications such as superconductivity and high-energy physics. Helium is also utilized as a lifting gas for airships and balloons due to its low density, making it safer than hydrogen, which is flammable.
Most helium on Earth is found in natural gas wells, particularly in regions like Texas, Oklahoma, and Kansas, as well as in some international locations such as Canada and Russia. It is produced through natural processes, including the radioactive decay of elements like uranium and thorium. Helium does not form compounds and escapes into space from the atmosphere, leading to a finite supply. The element was first discovered in 1868 during a solar eclipse, when astronomers identified a unique emission line from the sun.
Currently, helium is produced and purified for various uses, including in the aerospace industry and for deep-sea diving, where it serves as a safer alternative to nitrogen in breathing mixtures. Its unique properties and applications make helium an essential resource in both scientific and practical domains.
Helium (He)
Where Found
Helium is concentrated in some natural gaswells, particularly in Texas, Oklahoma, and Kansas. Helium is also found in the Earth’s atmosphere.
Primary Uses
The most important use of helium is as a cryogenic coolant, since it permits cooling to temperatures lower than any other substance. Helium is also used as a lifting gas for airships, as a replacement for nitrogen in the breathing gas for deep-sea divers, and as an inert atmosphere for welding.
Technical Definition
Helium (abbreviated He), atomic number 2, belongs to the last column of the periodic table of the elements. It has two naturally occurring isotopes and an average molecular weight of 4.003. Helium is a gas, having a density of 0.1637 gram/liter at 25° Celsius and 1 atmosphere of pressure. Helium boils at -268.9° Celsius. It is the most chemically inert element in the periodic table.
Description, Distribution, and Forms
Helium does not form any chemical compounds. It is the lightest of the noble gases, so light that it quickly escapes into space from the Earth’s atmosphere. Thus, much of the helium now found on the Earth was produced by radioactive decay. In excess of 130 million cubic meters of helium is produced annually in the United States. A majority of this helium is used by government agencies, including the Department of Energy and the National Aeronautics and Space Administration (NASA).
Small quantities of helium, pure helium 4, are produced by the radioactive decay of uranium or thorium in the Earth. In locations where uranium or thorium concentrations are high, helium collects in the same cavities as natural gas. The largest concentrations of helium are found in some natural gas wells in New Mexico, Texas, Oklahoma, Utah, and Kansas in the United States; in Saskatchewan and Alberta, Canada; in South Africa; and in Russia.
Helium is also present in the Earth’s atmosphere. Some of this helium was produced by radioactive decay in the Earth and subsequently escaped into the air. However, high-energy cosmic rays hitting the Earth’s atmosphere also produce helium by spallation, a process in which a heavier nucleus breaks into two or more lighter nuclei when it is hit by a high-energy particle. Radioactive decay produces only helium 4, while spallation produces both helium 3 and helium 4. Thus, atmospheric helium has a much higher content of helium 3 than the helium obtained from natural gas wells.
History
Helium was discovered in 1868. A French astronomer, Pierre Janssen, observed the emission spectrum of the Sun’s chromosphere during the August 18 solar eclipse. He saw a yellow-orange emission line that did not correspond to that of any known element. Later that year, both Janssen and an English astronomer, Sir Norman Joseph Lockyer, observed this emission again. Lockyer named this new element helium, for the Sun (helios in Greek).
In 1889, William Hildebrand, an American mineralchemist, extracted a gas from a uranium-bearing mineral, uranite. Sir William Ramsay, an English chemist, performed a similar extraction on cleveite, another uranium-bearing mineral. Ramsey sent the gas to Lockyer, who showed in 1895 that it had the same emission lines he previously observed in the Sun, providing the first identification of helium on Earth.
Obtaining Helium
The U.S. Bureau of Mines, which established three experimental plants to extract helium from the Petrolia natural gas field in clay County, Texas, had produced about 6,000 cubic meters of helium by 1920. Helium-bearing well gas, typically about 80 percent methane, is compressed and then treated to remove carbon dioxide, hydrogen sulfide, and water vapor. The remaining gas is cooled to a temperature of about -150° Celsius, which liquefies almost all the hydrocarbons, leaving nitrogen and helium in the gas phase. This gas is compressed again, then cooled to -196° Celsius, at which point the nitrogen liquefies, leaving almost pure helium in the gas phase.
Uses of Helium
Helium has a much lower density than air; thus a helium-filled balloon will rise. The first practical application of helium was as a lifting gas for lighter-than-air craft. Although hydrogen has an even lower density, making it a more efficient lifting gas than helium, the extreme flammability of hydrogen makes its use dangerous. The U.S. Navy experimented with rigid airships, called dirigibles, during the 1920’s and 1930’s. In the modern era, the Goodyear Aircraft Corporation built a series of nonrigid airships, called blimps, which have been used as platforms for aerial photography. Helium-filled balloons are also used for scientific research in the upper atmosphere.
In 1908, Heike Kamerlingh Onnes, a physicist at the University of Leiden, in Holland, liquefied helium by compressing it to a high pressure, cooling it, then allowing the helium to expand through a small opening. Expansion causes a gas to cool, and some of the helium liquefied.
Since the boiling point of helium under 1 atmosphere of pressure is -268.9° Celsius, material brought into contact with liquid helium cools rapidly. In 1911, Kamerlingh Onnes demonstrated that the electrical resistance of mercury vanishes at liquid helium temperature. He had discovered superconductivity.
Helium is used to dilute oxygen in the breathing gas used by deep-sea divers. Divers must breath an atmosphere at the same pressure as the surrounding water. At ocean depths the pressure is high, and both oxygen and nitrogen dissolve in body fluids. The oxygen is consumed, but the nitrogen remains in the fluids. If divers return suddenly to the surface, they can suffer the “bends,” which results when the nitrogen expands rapidly. The substitution of helium, the least soluble gas known, for nitrogen allows divers to operate at depth and then return to the surface more quickly.
Bibliography
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