Technetium · element 43
The first element made by humans, missing from Earth's rocks yet used in millions of medical scans every year
Key facts
For decades the periodic table had a hole beneath manganese. Mendeleev predicted the missing element, but every claim to have found it in minerals fell apart, for a simple and strange reason: element 43 has no stable form. Any that existed when the Earth formed decayed away long ago.
It was finally identified in 1937 in a scrap of molybdenum bombarded inside a particle accelerator, the first element produced artificially, and named from the Greek technetos, artificial. Today technetium-99m is the most widely used radioactive tracer in medicine, injected into tens of millions of patients a year.
Where it is found
Technetium is effectively absent from the Earth's crust. Its longest-lived isotopes have half-lives of a few million years, far too short to survive the 4.5 billion years since the planet formed. Minute traces do form when uranium-238 atoms in ore split spontaneously, as confirmed in 1962 in African pitchblende.
In 1952 the astronomer Paul Merrill found technetium lines in the spectra of certain red giant stars. Since it cannot have lasted since those stars were born, they must be making it now, the first direct proof that heavy elements are forged inside stars. On Earth the real source is nuclear reactors: technetium-99 is a common fission product, and the world's spent fuel holds many tonnes of it.
How it was discovered
Several false discoveries of element 43 were announced under names such as masurium, but none stood up. The genuine discovery came in 1937 at the University of Palermo. Emilio Segrè had visited Ernest Lawrence's laboratory at Berkeley and been given a discarded strip of molybdenum foil from the cyclotron, bombarded with deuterons for months.
Segrè and the mineralogist Carlo Perrier dissolved the foil and separated a radioactive fraction whose chemistry matched no known element but fitted perfectly beneath manganese. They proposed the name technetium in 1947. Segrè later shared a Nobel Prize for discovering the antiproton.
What we use it for
One isotope dominates. Technetium-99m has a half-life of six hours and emits a gamma ray of just the right energy for hospital cameras while delivering a low dose. Attached to different carrier molecules, it lights up bones to find fractures and tumours, maps blood flow through heart muscle, checks kidneys and locates lymph nodes into which a cancer might spread. It accounts for the large majority of diagnostic nuclear medicine worldwide.
Hospitals obtain it from generators nicknamed molybdenum cows: molybdenum-99, made in a few research reactors, decays into technetium-99m, which is washed out each morning with salt water. Beyond medicine, uses are limited by radioactivity. Pertechnetate ions protect steel from corrosion remarkably well but only in sealed systems, and technetium metal superconducts below about 8 kelvin, though it is far too scarce to exploit.
Reading the numbers
Technetium melts at about 2157 °C and boils at 4265 °C, placing it firmly among the refractory metals between molybdenum and ruthenium. Its density of about 11 grams per cubic centimetre is close to that of lead, so a coin-sized piece would feel very heavy. The atomic mass is listed as 98 in brackets rather than as a precise decimal, because with no stable isotope there is no natural mixture to average.
The configuration [Kr] 4d5 5s2 gives seven electrons outside the krypton core, the same count as manganese above it, so technetium forms the +7 pertechnetate ion just as manganese forms permanganate, and a +4 oxide. Only three ionisation energies, 702, 1470 and 2850 kJ/mol, have been measured, a reflection of how little material chemists have had to work with. Its electronegativity of 1.9 fits smoothly between molybdenum and ruthenium. Its instability lies in the nucleus, not the electrons: with an odd 43 protons, every possible neutron count leaves a nucleus that can lower its energy by decaying into more tightly bound molybdenum or ruthenium.
Safety and the environment
All technetium is radioactive. Technetium-99 emits weak beta particles and has a half-life of 211,000 years, so it is a hazard mainly if inhaled or swallowed, and a long-term concern in nuclear waste. Technetium-99m gives a medical dose comparable to a CT scan and has in effect disappeared from the body within a few days, which is why it is regarded as safe for routine diagnosis, including in children.
Pertechnetate dissolves readily and moves through soil, making technetium-99 a troublesome component of reprocessing waste. Discharges from Sellafield into the Irish Sea in the 1990s were detectable in lobsters and seaweed until treatment was improved. The fragile supply of molybdenum-99 from a handful of ageing reactors has caused shortages of medical technetium more than once.
Did you know?
- Technetium was the first element produced artificially, identified in 1937 in a discarded piece of cyclotron equipment posted from California to Sicily.
- In 1952 technetium was detected in the light of red giant stars, proving that stars are still manufacturing heavy elements today.
- Technetium-99m is used in most diagnostic nuclear medicine scans worldwide, amounting to tens of millions of procedures a year.
- The atomic mass of technetium is written as 98 in brackets because it has no stable isotope and therefore no natural average.
- Minute amounts of technetium do occur in uranium ore, created by the spontaneous splitting of uranium atoms.
- Lobsters caught near the Sellafield nuclear plant in the 1990s contained measurable technetium-99 from discharges into the Irish Sea.
More in the transition metals
Column-mates come first, since elements in one column have outer electrons arranged in a similar way and tend to behave alike; the rest are the nearest neighbours in the family.
See all 38 transition metals on one page, or browse all 118 elements.
Frequently asked questions
Why does technetium have no stable isotopes?
Stability depends on how tightly the nucleus is bound. Technetium has an odd number of protons, 43, and for every neutron count it might have, the neighbouring molybdenum or ruthenium nucleus with the same total mass is more tightly bound. A technetium nucleus can therefore always lose energy by decaying into one of them, so none of its isotopes lasts forever.
Is technetium dangerous in medical scans?
The dose from a technetium-99m scan is small, broadly similar to a CT scan, and the isotope's six-hour half-life means the radioactivity is almost entirely gone within a couple of days. The benefit of an accurate diagnosis normally far outweighs the tiny added risk. Patients are sometimes advised to limit close contact with young children for a day or so as a precaution.
Where does technetium come from?
Almost all technetium is made in nuclear reactors. Hospitals get technetium-99m from generators loaded with molybdenum-99, itself produced by irradiating uranium or molybdenum targets in a small number of research reactors. Larger amounts of long-lived technetium-99 accumulate in spent nuclear fuel.
Is technetium found in nature?
Only in traces. Tiny amounts form in uranium ores when uranium atoms split spontaneously, and technetium has been detected in the atmospheres of some red giant stars. There is no mineable source anywhere on Earth, which is why the element remained undiscovered until it was made artificially in 1937.
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Written by Anthony. Updated September 2026. Numerical data from Periodic-Table-JSON (CC BY-SA), cross-checked against the Technetium reference article. Spotted an error? Tell us.