helium
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What is helium?
Helium (He) is a chemical element that is an inert, odorless, colorless, and tasteless gas. It belongs to the noble gases in Group 18 of the periodic table and is the second lightest element. Helium remains a liquid until cooled to −268.9 °C (−452 °F), a lower boiling and freezing point than any other known substance. It can only be solidified by applying 25 atmospheres of pressure at 1 K (−272 °C, or −458 °F).
Helium is isolated from natural gas, yielding a gas that is 98.2 percent pure. To get 99.995 percent pure helium, other gases must undergo adsorption on cooled, activated charcoal. It can also be sourced in small amounts from air liquefaction.
Helium's stable isotopes are helium-3 ((^3)He) and helium-4 ((^4)He). Superfluidity occurs in both isotopes, but at different temperatures.
Helium is used for:
* Welding metals like aluminum.
* Rocket propulsion.
* Meteorology.
* Cryogenics.
* High-pressure breathing operations.2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
Where is helium found in nature?
Helium, the second most abundant element in the universe, is primarily concentrated in stars, where it is created through nuclear fusion of hydrogen. On Earth, helium is scarce in the atmosphere (0.0005 percent) and is found in small amounts in radioactive minerals, meteoric iron, and mineral springs.
However, significant quantities of helium (up to 7.6 percent) are found in natural gas in the United States, especially in Texas, New Mexico, Kansas, Oklahoma, Arizona, and Utah. Smaller reserves have been located in Algeria, Australia, Poland, Qatar, and Russia. Helium on Earth is generated by radioactive decay. Alpha particles, which are nuclei of helium-4, are emitted from the nuclei of heavier radioactive substances.
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What are some common uses of helium?
Helium is a versatile element with several common applications:
- Lifting gas Because it is nonflammable, helium is a safer alternative to hydrogen in balloons and airships.
- Welding Helium provides an inert atmosphere for welding metals like aluminum, preventing unwanted reactions with oxygen, nitrogen, or carbon dioxide.
- Cryogenics As the coldest substance in liquid form, helium is used as a coolant in cryogenics. It is essential in the study of superconductivity, as it cools materials to the required low temperatures.
- Leak detection Helium is used in mass spectrometers to detect leaks in vacuum systems.
- High-pressure breathing Mixed with oxygen, helium is used in scuba diving and caisson work because of its low solubility in the bloodstream, which prevents bubbles upon decompression.
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Why does helium make balloons float?
Helium makes balloons float because it is lighter than air. According to Archimedes’ principle, an object rises if its weight is less than the fluid it displaces. Because helium is the second lightest element, a balloon filled with helium weighs less than the air it displaces, resulting in a net upward force, or buoyancy.
Helium is a colorless, odorless, and tasteless gas that becomes liquid at -268.9 °C (-452 °F). It is used in meteorology as a lifting gas for instrument-carrying balloons.
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How is helium made or collected for industrial use?
Helium is extracted from natural gas by cooling other gases at high pressure until they liquefy, leaving helium in its gaseous state. This results in 98.2% pure helium. To achieve 99.995% purity, the gas undergoes adsorption using cooled, activated charcoal.
While some helium can be sourced from air liquefaction, the yield is relatively low, at approximately 112 cubic feet per 1,000 tons of air.
Industrially, helium serves as an inert atmosphere for welding metals like aluminum and as a coolant in cryogenics. It is also used to pressurize fuel tanks in rocket propulsion and as a lifting gas for meteorological balloons.
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What makes helium different from most other gases on the periodic table?
Helium, a noble gas, stands out from other gases due to its extreme inertness and unique physical properties. Its reluctance to react makes it useful for creating unreactive environments in welding and refining metals.
Helium has the lowest boiling and freezing points of any element; it can't be solidified at normal atmospheric pressure without applying external pressure. It has two stable isotopes, helium-3 and helium-4, which display superfluidity at very low temperatures, a property where it flows without resistance. Helium-4 is unique for having two liquid forms, one of which has high thermal conductivity. Due to its low solubility in fluids, helium is mixed with oxygen for deep-sea divers, preventing nitrogen bubbles in the blood upon decompression.
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helium (He), chemical element, inert gas of Group 18 (noble gases) of the periodic table. The second lightest element (only hydrogen is lighter), helium is a colorless, odorless, and tasteless gas that becomes liquid at −268.9 °C (−452 °F). The boiling and freezing points of helium are lower than those of any other known substance. Helium is the only element that cannot be solidified by sufficient cooling at normal atmospheric pressure; it is necessary to apply pressure of 25 atmospheres at a temperature of 1 K (−272 °C, or −458 °F) to convert it to its solid form.
| atomic number | 2 |
|---|---|
| atomic weight | 4.002602 |
| melting point | none |
| boiling point | −268.9 °C (−452 °F) |
| density (1 atm, 0 °C) | 0.1785 gram/liter |
| oxidation state | 0 |
| electron configuration | 1s2 |
History
Helium was discovered in the gaseous atmosphere surrounding the Sun by the French astronomer Pierre Janssen, who detected a bright yellow line in the spectrum of the solar chromosphere during an eclipse in 1868; this line was initially assumed to represent 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 so he named it the D3 line. Lockyer concluded that the D3 line was caused by an element in the Sun that was unknown on Earth; he and the chemist Edward Frankland used the Greek word for sun, hēlios, in naming the element. The British chemist Sir William Ramsay discovered the existence of helium on Earth in 1895. Ramsay obtained a sample of the uranium-bearing mineral cleveite, and, upon investigating the gas produced by heating the sample, he found that a unique bright yellow line in its spectrum matched that of the D3 line observed in the spectrum of the Sun; the new element of helium was thus conclusively identified. In 1903 Ramsay and Frederick Soddy further determined that helium is a product of the spontaneous disintegration of radioactive substances.
Abundance and isotopes
Helium constitutes about 23 percent of the mass of the universe and is thus second in abundance to hydrogen in the cosmos. Helium is concentrated in stars, where it is synthesized from hydrogen by nuclear fusion. Although helium occurs in Earth’s atmosphere only to the extent of 1 part in 200,000 (0.0005 percent) and small amounts occur in radioactive minerals, meteoric iron, and mineral springs, great volumes of helium are found as a component (up to 7.6 percent) in natural gases in the United States (especially in Texas, New Mexico, Kansas, Oklahoma, Arizona, and Utah). Smaller supplies have been discovered in Algeria, Australia, Poland, Qatar, and Russia. Ordinary air contains about 5 parts per million of helium, and Earth’s crust is only about 8 parts per billion.
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The nucleus of every helium atom contains two protons, but, as is the case with all elements, isotopes of helium exist. The known isotopes of helium contain from one to six neutrons, so their mass numbers range from three to eight. Of these six isotopes, only those with 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 other substances. The helium that is present on Earth is not a primordial component but has been generated by radioactive decay. Alpha particles, ejected from the nuclei of heavier radioactive substances, are nuclei of the isotope helium-4. Helium does not accumulate in large quantities in the atmosphere because Earth’s gravity is not sufficient to prevent its gradual escape into space. The trace of the isotope helium-3 on Earth is attributable to the negative beta decay of the rare hydrogen-3 isotope (tritium). Helium-4 is by far the most plentiful of the stable isotopes: helium-4 atoms outnumber those of helium-3 about 700,000:1 in atmospheric helium and about 7,000,000:1 in certain helium-bearing minerals.
Properties
Helium-4 is unique in having two liquid forms. The normal liquid form is called helium I and exists at temperatures from its boiling point of 4.21 K (−268.9 °C) down to about 2.18 K (−271 °C). Below 2.18 K, thermal conductivity of helium-4 becomes more than 1,000 times greater than that of copper. This liquid form is called helium II to distinguish it from normal liquid helium I. Helium II exhibits the property called superfluidity: its viscosity, or resistance to flow, is so low that it has not been measured. 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. By contrast, the less plentiful helium-3 forms three distinguishable liquid phases of which two are superfluids. 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. Osheroff, David M. Lee, and Robert C. Richardson of the United States in 1972.
A liquid mixture of the two isotopes helium-3 and helium-4 separates at temperatures below about 0.8 K (−272.4 °C, or −458.2 °F) into two layers. One layer is practically pure helium-3; the other is mostly helium-4 but retains about 6 percent helium-3 even at the lowest temperatures achieved. The dissolution of helium-3 in helium-4 is accompanied by a cooling effect that has been used in the construction of cryostats (devices for production of very low temperatures) that can attain—and maintain 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 other components at low temperatures and under high pressures. Adsorption of other gases on cooled, activated charcoal yields 99.995 percent pure helium. Some helium is supplied from liquefaction of air on a large scale; the amount of helium obtainable from 1,000 tons (900 metric tons) of air is about 112 cubic feet (3.17 cubic meters), as measured at room temperature and at normal atmospheric pressure.
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Helium is used as an inert-gas atmosphere for welding metals 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-carrying balloons); in cryogenics (as a coolant because liquid helium is the coldest substance); and in high-pressure breathing operations (mixed with oxygen, as in scuba diving and caisson work, especially because of its low solubility in the bloodstream). Meteorites and rocks have been analyzed for helium content as a means of dating.