Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Technetium is the lightest chemical element without any stable isotopes. Its atomic number is 43 and it has the symbol Tc. Nearly all of technetium is produced synthetically and only minute amounts are found in nature. Naturally occurring technetium occurs as a spontaneous fission product in uranium ore or by neutron capture in molybdenum ores. The chemical properties of this silvery gray, crystalline transition metal are intermediate between rhenium and manganese.