262 | The History and Use of Our Earth’s Chemical Elements
262 | The History and Use of Our Earth’s Chemical Elements
ORIGINOFNAME: FromtheGreekwordhelios,meaningthe“sun.”Throughtheprocess ofspectrometry,itwasdiscoveredonthesunbeforeitwasfoundonEarthin1868. ISOTOPES:Thereareeightisotopesofhelium.Twoofthesearestable.TheyareHe-3, whichmakesupjust0.000137%ofnaturalheliumfoundonEarth,andHe-4,which accountsfor99.999863%ofthenaturalabundanceofheliumonEarth.Anotheriso- tope,He-5,isanextremelyrareradioisotopethatdecaysbyemittingbetaparticlesto formlithium-6andlithium-8.
ELECTRONCONFIGURATION EnergyLevels/Shells/Electrons Orbitals/Electrons
1-K=2
s2
Properties Helium is a colorless, odorless, and tasteless inert gas that is noncombustible and is the least
soluble of any gas in water and alcohol. As a gas, it diffuses well in solids. Helium’s freezing point is –272.2°C, and its boiling point is –268.93°C. Both temperatures are near absolute zero (–273.13°C, or –459.4°F), where all molecular and thermal motion ceases. Liquid helium has the lowest temperature of any known substance. Helium’s density is 0.0001785g/cm 3 .
Helium is the only element that cannot be converted into a solid by lowering the tem- perature. At normal pressure it remains a liquid at near absolute zero, but if the pressure is increased, it then turns into a solid.
Characteristics When a second proton and two neutrons are added to a hydrogen nucleus, a helium atom
can form after it collects two electrons. Helium is the most inert of all the noble group 18 gases. It is so inactive that it does not even combine with itself. As a gas, helium remains as
a single atom. The nuclei of helium are called alpha particles, each of which has a charge of +2 and an atomic mass of 4. No stable compound of helium has ever been found. However, it is possible for an atom of hydrogen to combine with helium (and other light noble elements) under special conditions to form HeH + , an unstable ion.
Helium is not plentiful on Earth and is only the sixth most abundant gas in the atmo- sphere. It does not accumulate in the atmosphere because it is lighter than air. Some amount of helium continually escapes into space from the outer atmosphere of the Earth.
Liquid helium exhibits some unusual characteristics when supercooled. First, it is the only element that will not turn into a solid by just using pressure. Heat must be removed as the pressure is increased, but helium will freeze at –272.2°C, which is the lowest temperature sci- entists have ever achieved. Second, it is an excellent conductor of heat. As a supercold liquid, it will move toward heat—even flow up the sides and over the top of a container.
263 AbundanceandSource
Guide to the Elements |
Helium is the 73rd most abundant element on Earth, but it is the second most abundant element in the universe, after hydrogen. Together, helium and hydrogen make up 99.9% of all the elements in the universe, but helium makes up only a small trace of the elements on Earth.
Most likely, helium was the first element to be formed after hydrogen during the Big Bang formation of the universe. The theory is that hydrogen atoms combined under great heat and pressure to form helium atoms. The Earth’s current helium originally came from the natural decay of radioactive elements deep in the Earth. Much of it seeps up to the surface and escapes into the atmosphere, or it mixes with natural gas deposits deep in the Earth. Like hydrogen, it is a very light gas that escapes through cracks in the Earth’s crust and sooner or later escapes from Earth’s gravity into the atmosphere.
Helium can be obtained from the atmosphere by lowering the temperature of air until it liquefies. All the other gases in air will turn to a liquid except helium, because it has the low- est boiling point. Since helium, at this stage of cooling, will be the only vapor left, it can be removed as a pure gas. It is commercially more profitable to produce helium by separating it from a mix of natural underground gases, where its concentration is greater that in the atmo- sphere. Raw natural gas is a mixture of methane, nitrogen, and helium, with traces of other gases. The nitrogen and helium are separated from the methane, which is used as a fuel. This separation is accomplished by fractional distillation wherein the temperature is reduced and the gases are liquefied. As the temperature is reduced, methane is liquefied first, then nitro- gen, leaving helium to be collected and sold commercially. Helium is produced in Oklahoma, Kansas, New Mexico, Arizona, and Canada by liquefying natural gas and “boiling off” the other gases. Helium is then purified to 99.995%. Amarillo, Texas, is one of the major centers for the production of helium in the United States. Over three billion cubic feet of helium is produced in the United States, where there is a military-reserve “storage” supply in natural caverns of over 32 billion cubic feet of helium. Most of the world’s supply of helium comes from the United States.
History Two astronomers identified helium independently as a part of the sun’s atmosphere before
it was found on Earth. Using a prism, Pierre-Jules-César Janssen (1824–1907) of France observed a yellow line in the sun’s spectrum during a total solar eclipse in India in 1868. (Spectral emission lines refer to the wavelengths of light given off by each element when it is heated to a high temperature. Each element gives off a unique colored line that can be used to identify individual elements—somewhat like fingerprints.) At about the same time, an English astronomer Sir Norman Joseph Lockyer (1836–1920) realized that the wavelength of 587.49 nanometers was not related to any known element at that time. He identified this as a new element on the sun and named it helium.
It was not until 1895 that Scottish chemist Sir William Ramsay (1852–1916) first found helium on Earth when he experimented with uranium and subsequently collected the gases that were produced when he treated his samples with acid. He sent the gases to Sir William Crookes (1832–1919), who identified one gas as helium. Two Swedish chemists, Per Theodor Cleve