Helium, << HEE lee uhm, >> is a lightweight gas and chemical element. Hydrogen is the only element that weighs less than helium. Helium is called an inert gas or noble gas. These terms are used because helium does not combine with other elements.
Helium makes up only a small fraction of Earth’s matter. But it is one of the most common elements in the universe. The sun and other stars are made mostly of helium and hydrogen. The energy of these stars is produced when hydrogen atoms fuse (join together) to form helium atoms. This process is also what gives the hydrogen bomb its energy (see Nuclear weapon).
On Earth, helium occurs in natural gas deposits and in the atmosphere. The atmosphere contains about 5 parts of helium per million parts of air. Because helium is so light, it constantly escapes from the atmosphere and drifts into space. But the lost helium is replaced by radioactive minerals that shoot out alpha particles (helium nuclei). Each alpha particle captures two electrons to form a complete helium atom.
In 1868, the astronomers Pierre J. Janssen of France and Sir Joseph Lockyer of England discovered helium in the sun while studying the sun with an instrument known as a spectroscope. Lockyer and Sir Edward Frankland, an English chemist, suggested the name helium. The name comes from the Greek word helios, which means sun.
In 1895, helium was first found on Earth. The Scottish chemist Sir William Ramsay and the Swedish chemists Nils Langlet and Per Theodor Cleve discovered it in the mineral clevite.
Uses.
About 700 million cubic feet (20 million cubic meters) of helium are used in the United States yearly. Federal agencies use about three-fourths of this amount and private industries use the rest.
The government’s chief use of helium is in maintaining the proper pressures in rockets. Pressure must be maintained in rocket fuel tanks during flight, or the thin walls of the large tanks might collapse as the fuel drains from them. Helium also produces the pressure that forces fuel into rocket pumping systems.
The largest industrial use of helium is in helium arc welding, sometimes called heliarc welding. The inert helium keeps oxygen in the air from reaching the metal. If oxygen reaches the metal, it may cause the metal either to burn or to corrode. Helium is used to prevent chemicals from reacting with other elements during storage, handling, and transportation.
Helium is also used to fill scientific balloons. The balloons rise to high altitudes, because helium is lighter than air. In air, helium has 92 percent of the lifting ability of hydrogen. It is safer than hydrogen because it will not burn, as hydrogen will.
Persons with asthma or other breathing difficulties must sometimes inhale a mixture of helium and oxygen. The mixture enters the lungs more easily than air because the helium atoms are lighter than the nitrogen molecules of the air. Divers sometimes breathe a mixture of helium and oxygen to avoid a painful illness called nitrogen narcosis. Nitrogen narcosis usually occurs at depths below 100 feet (30 meters). The pressure of the water on divers’ bodies forces bubbles of nitrogen gas from the air into their blood when they breathe. The blood carries the nitrogen to the brain. This illness causes the divers to lose the ability to think clearly, and they may do dangerous things or pass out.
Production.
Most of the world’s helium comes from five natural-gas fields in the United States: (1) the Cliffside field in the Texas Panhandle, (2) the Greenwood field in Kansas and Colorado, (3) the Hugoton field in Kansas, Oklahoma, and Texas, (4) the Keyes field in Oklahoma, and (5) the Panhandle field in Texas. These fields contain an estimated 180 billion cubic feet (5 billion cubic meters) of helium. Helium plants in the United States produce about 2 billion cubic feet (57 million cubic meters) of helium each year.
Natural gas from some wells contains up to 8 percent helium. Helium is purified by cooling the natural gas until all gases except helium, argon, hydrogen, and nitrogen change to liquid. Hydrogen is then burned out of the remaining mixture, and argon is absorbed by charcoal at low temperatures. Nitrogen often remains in helium as an impurity. Helium that is 99.995 percent pure is called grade A helium. Crude helium contains about half helium and half nitrogen.
Properties.
Helium is a colorless, odorless, and tasteless gas. Its chemical symbol is He. Its atomic number (number of protons in its nucleus) is 2. Its relative atomic mass is 4.002602. An element’s relative atomic mass equals its mass (amount of matter) divided by 1/12 of the mass of carbon 12, the most abundant form of carbon. Helium’s density is 0.1664 milligram per cubic centimeter at 20 °C. It changes to liquid when it is cooled to –268.9 °C, about 4 °C above absolute zero. Because helium can be cooled to such a low temperature without freezing, it is used as a liquid refrigerant in low temperature devices and in cryogenics research (see Cryogenics). In addition, helium is the only chemical element that cannot be changed to a solid by cooling alone under ordinary pressures. It must be cooled and compressed. Helium freezes solid at –272.2 °C under a pressure of 26 times atmospheric pressure. For information on the position of helium on the periodic table, see the article Periodic table.
Liquid helium is one of the strangest of all liquids. Unlike most liquids, it conducts heat extremely well, it flows toward relatively warm places, and it expands instead of contracting when it cools. Liquid helium forms a film over everything it touches. This film can act as a siphon, carrying helium over the side of a container to a lower level.
See also Airship; Balloon; Element, Chemical (Periodic table); Ramsay, Sir William; Superfluid.
