Technetium is a transition element in Group 7 of the periodic table. It has an atomic number of 43, an atomic mass of 97.9072, and a chemical symbol of Tc.

Properties

All isotopes of technetium are radioactive, with the most stable being technetium-98, whose half life is about 4.2 x 10⁶ years. The element is a silver-gray metal with a melting point of 4,000°F (2,200°C) and a density of 11.5 grams per cubic centimeter. The chemical properties are generally not of as much interest to scientists as are its radioactivity, although it is known that its properties are similar to those of manganese and rhenium, in the same group of the periodic table.

Occurrence and Extraction

Some scientists believe that minute amounts of technetium may be present in the Earth's crust, in conjunction with other radioactive materials, such as uranium and radium. However, it has never been found on the Earth, although it has been discovered in certain young stars. The element can be made artificially in particle accelerators.

Discovery and Naming

By the 1920s, scientists were relatively certain that an element with atomic number 43 must exist. But no element with that number had as yet been found to fill the designated location in the periodic table. Finally, in 1937, the element was found by Italian physicist Emilio Segrè (1905-89) and his colleague Carlo Perrier in a sample of molybdenum that had been bombarded with deuterons in a cyclotron at the University of California at Berkeley. Segrè and Perrier suggested the name technetium for the new element after the Greek word technetos, meaning "artificial."

Uses

Technetium is used in very limited amounts to make an alloy known as technetium-steel, which is very resistant to corrosion. Its applications are very limited, however, because of the radioactivity it contains. One isotope of technetium is of special value in medical diagnosis, technetium-99m. This isotope decays with a half life of about six hours, an ideal half life for a diagnostic radioisotope. The half life is ideal because it lasts long enough to produce the radiation needed to diagnose the condition of an organ, but it is short enough to present no serious long-term threat to the body.