Deuterium is a non-radioactive isotope of hydrogen characterized by an extra proton. It is an odorless, flammable gas that exists in a diatomic state. The properties of deuterium and deuterium oxide are different from those of ordinary hydrogen and water. For example, the melting points of H2 and D2 are, respectively, -434.6 °F (- 259.2° C) and -425.9 °F (-254.4° C). The boiling points of H2O and D2O are, respectively, 212° F (100.0° C) and 214.52° F (101.4 ° C).
The discovery of isotopes by Frederick Soddy in 1913 spurred a special interest in the simplest chemical element, hydrogen. Isotopes of most elements differ from each other by only a few percent in their atomic weight, but an isotope of hydrogen would differ by at least 100% from ordinary hydrogen-1. The lightest possible isotope would consist of a proton and a neutron, for a mass of 2, compared to ordinary hydrogen, with only a single proton and a mass of 1. Scientists were eager to see how such a large mass difference might affect the properties of the heavier hydrogen and to begin using the isotope in research once it was found.
The discovery of the heavier isotope of hydrogen was made in 1931 by Harold Urey at Columbia University. Urey reasoned that if "heavy hydrogen" did exist, it would evaporate from the liquid state more slowly than would normal hydrogen. This difference should make it possible, he thought, to separate the heavier and lighter isotopes from each other.
To test this hypothesis, Urey allowed four liters of liquid hydrogen to evaporate very slowly until only a single milliliter of the liquid remained. Then he examined the spectral pattern produced by this sample of hydrogen. He found the presence of some very faint lines that are not present in the spectrum of ordinary hydrogen.
Urey concluded from this observation that the final milliliter of liquid hydrogen was richer in heavy hydrogen--which he named deuterium--than is ordinary hydrogen. For this discovery, Urey was awarded the Nobel Prize in chemistry in 1934. Shortly thereafter, American chemist Gilbert N. Lewis prepared the first sample of water that contained all deuterium atoms combined with oxygen. This "heavy water" is also known as deuterium oxide and has the chemical formula, D2 O.
Deuterium has many important applications. Its nucleus, called a deuteron, is widely used in particle accelerator research. With a mass twice that of a proton, it is often able to penetrate a target nucleus more effectively than can other nuclear "bullets."
The isotope is also used in research. Its unusually large mass makes it an ideal tracer in biological studies. Deuterium is also an important component of nuclear fusion ("thermonuclear" or "hydrogen") bombs. At temperatures above 20 million degrees Celsius, deuterium fuses with another isotope of hydrogen, tritium (hydrogen-3) to form helium, with the release of very large amounts of energy.
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