Helium | Research & Encyclopedia Articles

Helium

Helium is a noble gas element denoted by the atomic symbol H. It has an atomic number of 2, and the average atomic weight of its isotopes is 4.0026. It is a colorless, odorless gas which is present in all natural gas sources.

In many respects, helium is one of the most unusual elements known to science. Helium is far more abundant throughout the rest of the universe than it is here on earth. In fact, helium was first found to exist on the Sun, for which it was named after the Greek word helios. In 1868, French astronomer Pierre Janssen (1824-1907) went to India to study a total solar eclipse. Although lame from a childhood accident, Janssen traveled the world in pursuit of such astronomical events. During the eclipse, he analyzed the wavelengths, or colors, displayed in the Sun's spectrum of light and found a yellow spectral line that he did not recognize, which could indicate the existence of a new element.

Janssen reported this unusual line to Sir Joseph Lockyer (1836-1920), an English astronomer who had gained a worldwide reputation for analyzing light waves. Lockyer went out on a limb and declared publicly that the yellow line (which Lockyer himself observed a few months later than Janssen) did indeed represent a new element. Most people didn't believe him. The instrument used to analyze light waves, called the spectroscope, had only recently been invented, and the scientific establishment was not ready to recognize an entirely new element on the basis of this technology. But Lockyer and Janssen lived long enough to see helium's existence verified, and today they are credited with its discovery.

Some 25 years later, Sir William Ramsay became interested in a mysterious bubble of gas left over when nitrogen from the air was combined with oxygen. This discrepancy was first noted by Henry Cavendish in the 1780s. This gas, Ramsay deduced, could be responsible for a scientific problem posed by John William Strutt (Lord Rayleigh), who had found that nitrogen extracted from the air was heavier than nitrogen obtained from chemical compounds. The mystery gas turned out to contain not nitrogen, but a family of five new gases. Although the first gas to be identified was argon, Ramsay soon produced the second gas in his laboratory. Spectroscopic analysis of the gas revealed unique spectral lines but, more astonishing to Ramsay, these lines were identical to those observed earlier by Lockyer and Janssen in the spectrum of the Sun. In 1895, Ramsay announced the discovery of helium on Earth, verifying the previous discovery of solar helium.

Several scientists set out to learn as much as possible about this exciting new gas, which appeared to be related to the radioactive decay of uranium. The science of radioactivity had just begun, and little was known about the radioactive decay process or the subatomic structure of atoms and molecules. By 1903, Ramsay and British chemist Frederick Soddy had demonstrated that the breakdown of both uranium and radium would produce helium atoms. A few years later, Australian physicist Ernest Rutherford proved that radiation carrying a positive electric charge (which he named alpha rays) was actually a stream of helium atoms with their negative charge (electrons) stripped off. Eventually, this work led to Rutherford's definition of the atom's fundamental positively charged particle, the proton.

Other physicists soon began attempting to liquefy and solidify helium by cooling it. To study the behavior of gases, scientists must measure their characteristics (such as volume, pressure, and temperature) very accurately, and low temperatures make it possible to obtain this critical information. But helium is unique in that it remains a gas at colder temperatures than any other element, and it is the only substance known that refuses to freeze solid even at absolute zero. The Dutch physicist Heike Kamerlingh Onnes finally succeeded in liquefying helium in 1908, at a temperature only slightly above absolute zero. After Onnes's death in 1926, his assistant Willem Keesom (1876-1956) managed to solidify helium by applying high pressure to the liquid, in addition to super-cold temperature.

This early research has since opened up a whole new field of low-temperature science called cryogenics. Today, helium's special properties make it indispensable as a refrigerant in research on superconductivity and in the development of modern supercomputers, whose switches must be kept very cold. Also, at very low temperatures, a certain form of helium exhibits a phenomenon called superfluidity--it suddenly transforms into a strange liquid, unlike any other, that has no measurable resistance to flow. This means that it can carry heat hundreds of times more effectively than pure copper, which is the best metallic conductor.

On the Sun, helium is created by the fusion of hydrogen atoms, which gives us solar energy. This fusion process, which was first explained by German-American chemist Hans Bethe in the late 1930s, also powers the stars and gives them their light. Scientists estimate that helium accounts for 23 percent of the total mass of the universe. But our atmosphere contains much less helium than could be expected, considering the fact that helium is constantly being produced by uranium and other radioactive substances. Scientists think that most of this helium simply escapes into space because it is so lightweight.

Although helium can be separated from air like other inert gases, the process is relatively expensive, and most commercial supplies of helium are produced from a few natural gas fields in the southwestern United States. Around 1920, Frederick Cottrell (1877-1948) invented a practical technique for separating helium from natural gas, and during World War I, the American astronomer George Hale (1868-1938) was responsible for coordinating the extraction of helium from gas wells. Because of its lightness and nonflammability, helium was needed to inflate military blimps, and it is still used for weather balloons and other high-altitude research.

Although helium's value in high-technology applications will continue to increase, most helium today is consumed in arc welding, where it is used as a gas shield to protect the metal from oxidation. Helium is also used with neon in gas lasers and as a carrier gas in chromatographic analysis of chemicals. Deep-sea divers often breathe it in a mixture with oxygen to avoid getting the "bends," which occur when gas dissolved in the blood forms bubbles as the diver rises to the surface. Helium mitigates this effect because it does not dissolve in the blood as easily as its alternative, nitrogen.