Technetium is a chemical element with the symbol Tc and atomic number 43. It is the lightest element with no stable isotopes. All its isotopes are radioactive, although some have half-lives long enough to be found in nature. Technetium was discovered in 1937 by Carlo Perrier and Emilio Segrè, and is the only element whose discovery is solely credited to artificial production.

Technetium is a silvery-gray, lustrous metal. It is soft, ductile, and malleable. It is resistant to corrosion and tarnishing. Technetium is a poor conductor of electricity.

Technetium reacts with oxygen to form the oxide TcO2. It reacts with hydrogen to form the hydride TcH2. It reacts with halogens to form the halides TcCl4, TcBr4, and TcI4. It reacts with sulfur to form the sulfide TcS2.

Technetium is used in nuclear medicine as a radioactive tracer. It is also used in the production of gamma rays for industrial and medical purposes.