Technetium

Technetium (symbol Tc, atomic number 43) is the lightest element that has no stable isotopes—all of its forms are radioactive. Along with promethium, it is one of only two radioactive elements that have stable neighbors on both sides in the periodic table. While technetium is primarily produced artificially, trace amounts do occur naturally: it appears as a spontaneous fission product in uranium and thorium ores (thorium ore being the most common natural source) and can also result from neutron capture in molybdenum ores. This silvery gray, crystalline transition metal sits in group 7 of the periodic table, between manganese and rhenium, and its chemical behavior falls between those two elements. The most abundant naturally occurring isotope is 99Tc, but it exists only in minuscule traces. Many of technetium’s properties were anticipated by Dmitri Mendeleev before its actual discovery. Noticing a gap in his periodic table, Mendeleev predicted the missing element and gave it the provisional name ekamanganese (Em). In 1937, technetium became the first element to be produced predominantly by artificial means, which inspired its name—from the Greek *technetos*, meaning “artificial,” plus the suffix *-ium*. A short-lived gamma-ray–emitting nuclear isomer, technetium-99m, is widely used in nuclear medicine for diagnostic tests, including bone cancer detection. The ground state of technetium-99 serves as a source of beta particles without gamma rays. Commercially, long-lived technetium isotopes are byproducts of uranium-235 fission in nuclear reactors and are extracted from spent fuel rods. Although the longest-lived technetium isotope has a half-life of only 4.21 million years, its detection in red giants in 1952 provided key evidence that stars can produce heavier elements. Between the 1860s and 1871, early versions of the periodic table created by Dmitri Mendeleev included a gap between molybdenum (element 42) and ruthenium (element 44). In 1871, Mendeleev predicted that this missing element would sit directly below manganese and share similar chemical properties. He gave it the provisional name eka-manganese—*eka* being the Sanskrit word for “one”—because it was one place down from the known element manganese.