Technetium (Tc)
“Every atom of it is radioactive and no mine on Earth holds it — yet hospitals inject it into patients millions of times every year.”
How its electrons are arranged
Computed from the aufbau principle, with known real-world exceptions applied automatically.
The notes
Characteristics
- No stable isotope exists — every technetium atom is radioactive; configuration [Kr] 4d⁵ 5s² places it in Period 5, Group 7.
- The medical star Tc-99m has a 6-hour half-life and emits a clean 140 keV gamma ray — long enough to image an organ, short enough to fade quickly.
- Chemically it behaves like a lighter rhenium, sitting between manganese and rhenium in Group 7 with states up to +7 (the pertechnetate ion TcO₄⁻).
- Tc-99 is a major product of uranium fission, so spent nuclear reactor fuel is its only practical “ore”.
A silvery-grey radioactive metal that tarnishes slowly in moist air; samples are normally seen only as sealed hospital capsules or tiny laboratory traces. Uniquely among the lighter elements, no stable form of it exists anywhere in nature.
Where you meet it
✦ Uses
- Tc-99m radiopharmaceuticals for bone scans, heart perfusion tests and organ imaging — the world’s most-used medical radioisotope, with tens of millions of scans each year.
- Trace doses protect steel from rusting in closed water-heating systems, where a few parts per billion do the job.
- A precisely known Tc-99 gamma source for calibrating radiation monitors in hospitals and nuclear labs.
- Research source for studying chemical bonding of radioactive metals, since it is the lightest purely radioactive element.
◍ Everyday examples
- The nuclear medicine department of a large hospital — a bone scan for a hairline fracture or a heart stress test almost certainly involves Tc-99m.
- Spent reactor fuel rods in a nuclear power plant are humanity’s only practical stockpile of technetium.
- Red giant stars show technetium lines in their spectra — the element you “meet” every time you look at certain orange stars in the night sky.
History & name
Mendeleev left a gap for element 43 beneath manganese, and chemists hunted it in vain for decades — a 1925 claim of “masurium” by German researchers could never be verified. The breakthrough came in 1937, when Emilio Segrè and Carlo Perrier in Italy examined a molybdenum foil that Ernest Lawrence’s team had bombarded with deuterons in the Berkeley cyclotron. Its stubborn radioactivity turned out to be a brand-new element: the first ever created by human hands. In 1947 the discoverers named it technetium, from the Greek technetos, “artificial”. Then in 1952 astronomers found its spectral lines in red giant stars — living proof that heavy elements are forged inside stars.