Technetium << tehk NEE shee uhm >> was the first artificially created chemical element. The Italian physicists Carlo Perrier and Emilio Segrè first isolated it in 1937. The element appears as a silvery metal or gray powder. Its chemical symbol is Tc. Its atomic number (number of protons in its nucleus) is 43. Technetium resists oxidation but can be oxidized by nitric or sulfuric acid.
Technetium has many different isotopes. Isotopes are forms of an element with the same number of protons but different numbers of neutrons. The most stable isotope of technetium has an atomic mass number (total number of protons and neutrons) of 98. Technetium 98 has a half-life of 4.2 million years—that is, due to radioactive decay, only half the atoms in a sample of technetium 98 would still be atoms of that isotope after 4.2 million years. Physicians sometimes inject patients with an isotope called technetium 99m to produce images of body tissues. That isotope has a half-life of around 6 hours, so it does not remain in the body for long after medical tests.
Perrier and Segrè obtained the first technetium from a sample of molybdenum that had been bombarded with deuterons (particles consisting of one proton and one neutron). The scientists proved that the bombardment resulted in the addition of a proton to the nucleus of the molybdenum atom, forming technetium. They thought the new element, which they called masurium, would be easy to find in nature. However, they discovered that natural processes produce only tiny amounts of the element. The name was then changed to technetium, which comes from the Greek word for artificial. Technetium has been obtained in large quantities as a by-product of atomic fission (the splitting of atoms) to produce energy in nuclear power plants. However, the supply for use in medical imaging is now reduced as older nuclear plants that produced technetium 99m are shut down.
Technetium melts at 2172 °C and boils at 4877 °C. It has a density of 11.5 grams per cubic centimeter at 25 °C. Chemists classify technetium as a transition metal. For information on the position of technetium on the periodic table, see the article Periodic table.
