Atomic number 43

Technetium

Tc
+ phase
− phase

Shells Orbitals 4d 5s

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43 electrons in 5 shells: 2, 8, 18, 13, 2.

Shells are a teaching model: an electron does not travel on a ring at a fixed distance.

Category: Transition metal
Period: 5
Group: 7
Block: d
Atomic mass: 96.90636 Da (longest-lived isotope)
Electron configuration: [Kr] 4d⁵ 5s²
Phase at 25 °C: solid
Melting point: 2157 °C
Boiling point: 4265 °C
Density: 11 g/cm³
Electronegativity (Pauling): 1.9
Discovered: 1937, Carlo Perrier and Emilio Segrè

Neighbours in the table

Mo Ru

Element 43 was predicted from the periodic table before anyone held a sample, Los Alamos records. A claim in 1925 announced the element under the name masurium, a report later found to be erroneous, according to Los Alamos.

In 1937 Carlo Perrier and Emilio Segrè, working in Italy, isolated it from molybdenum bombarded with deuterons, the nuclei of heavy hydrogen, Jefferson Lab records. Los Alamos adds that a molybdenum sample from E. Lawrence, struck in the Berkeley cyclotron, also held it. Technetium was the first element produced artificially, according to Los Alamos, and its name comes from technetos, Greek for artificial.

Every one of technetium’s isotopes is radioactive, and below atomic number 83 only promethium shares that trait, according to Los Alamos. PubChem gives the mass of its longest-lived isotope, 96.906 Da, which is the mass of technetium-97. That isotope decays by electron capture, its nucleus taking in one of the atom’s own electrons. Its half-life, the time in which half of a sample decays, is 4.21 million years in the IAEA’s evaluation.

Technetium-98, which Jefferson Lab calls the most stable isotope, lasts 4.2 million years. It becomes ruthenium-98 by beta decay, in which a neutron in the nucleus turns into a proton and an electron is thrown out.

Where it is found

In Jefferson Lab’s account, technetium has never turned up naturally anywhere on Earth. Technetium-99, though, was found in pitchblende, a uranium-rich ore from Africa, by B. T. Kenna and P. K. Kuroda in 1962, Los Alamos records. The traces were extremely minute and had formed by spontaneous fission of uranium-238, the splitting of its nuclei without outside help. Very small natural amounts occur in the crust, according to EPA, though most technetium is made by people.

Far beyond Earth, its spectral lines, the pattern of wavelengths its atoms absorb or give out, appear in S-, M- and N-type stars. Its presence in stellar matter is prompting new theories of how stars build heavy elements, according to Los Alamos.

On Earth the working supply comes from reactors. Technetium-99 forms when uranium nuclei split in reactor fuel, so large quantities have built up, and today’s stock runs to kilograms, according to Los Alamos. It is also a component of nuclear waste, EPA notes. Air, seawater, soils, plants and animals all carry very low concentrations, and brown algae and some sea animals concentrate it in their bodies.

Why it matters

Most human contact with technetium comes from the deliberate use of technetium-99m in nuclear medicine, EPA says. The m stands for meta state, Los Alamos explains: an excited nucleus that, in Haz-Map’s summary, sheds its extra energy as a gamma ray by isomeric transition. Beta-minus decay accounts for a further 0.0037 per cent, and the half-life is 6.0066 hours, in the Atomic Mass Data Center’s data; Los Alamos gives 6.01 hours.

Three things suit it to medical tests, in Los Alamos’s account: that short half-life, the energy of its gamma ray and technetium’s ability to bond to many biologically active molecules.

Kidney, liver, bone and heart imaging all use it, according to IUPAC’s isotope notes in PubChem’s record. A variety of tumours absorb technetium-99m radiopharmaceuticals, drugs carrying a radioactive label, and single-photon emission computed tomography (SPECT) then images them. In heart imaging the isotope can replace thallium, whose medical demand keeps falling because alternatives such as technetium-99m perform better and are easier to obtain, the US Geological Survey reports.

The isotope comes from the decay of molybdenum-99, in Haz-Map’s summary, and that molybdenum-99 forms when molybdenum-98 captures a neutron, according to Jefferson Lab. Beyond medicine, a little technetium slows the corrosion of steel, though its radioactivity confines that use to closed systems. Technetium-95m serves in tracer work, Los Alamos notes.

Properties

Properties of technetium Standard atomic weights from IUPAC/CIAAW (abridged, 2024); other values from PubChem's periodic table, kelvin converted to °C.
Property	Value	Unit	Source
Atomic number	43
Atomic mass	96.90636 Da	Da	PubChem, longest-lived isotope
Melting point	2157 °C	°C	Los Alamos: 2157 °C
Boiling point	4265 °C	°C	Los Alamos: 4265 °C
Density	11 g/cm³	g/cm³
Electronegativity (Pauling)	1.9
Electron configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d⁵
Phase at 25 °C	solid

This element has no standard atomic weight; the atomic mass shown is that of its longest-lived isotope, as PubChem gives it.

Safety

Every isotope of technetium is radioactive, and the hazard it poses is ionising radiation. In Haz-Map’s radionuclide summary, technetium-99m is the most important radionuclide, with the total body as its critical organ and a low internal-toxicity rating. Technetium-99 can pose a health risk once inside the body, where it gathers in the gut and the thyroid, according to EPA, though the body keeps excreting it. The full reference sheet is PubChem’s Laboratory Chemical Safety Summary for technetium.

Questions

Does technetium have a stable isotope?

No. Every technetium isotope is radioactive. The Atomic Mass Data Center's table in PubChem lists nuclides from technetium-83 to technetium-122. Three are long-lived: technetium-97 (4.21 million years in IAEA's evaluation), technetium-98 (4.2 million years) and technetium-99 (about 211,000 years). PubChem gives the mass of its longest-lived isotope, 96.906 Da, that of technetium-97.

What are the oxidation states of technetium?

Its common oxidation states are +7, +5 and +4 according to Los Alamos, and +7, +6 and +4 according to Jefferson Lab. In Chem1's account, d electrons let transition metals show several valences, and technetium's configuration is [Kr] 4d⁵ 5s². Under oxidising conditions, technetium(VII) exists as the pertechnetate ion, TcO₄⁻, and its chemistry resembles that of rhenium, Los Alamos says.

What does technetium metal look like?

Technetium is a silvery-grey metal that tarnishes slowly in moist air, according to Los Alamos, and it melts at 2157 °C. Concentrated sulfuric acid, nitric acid and aqua regia all dissolve it, yet hydrochloric acid of any strength does not dissolve it. Cooled to about −262 °C or lower, the metal becomes an excellent superconductor, carrying electric current with no resistance, Los Alamos adds.

How long does technetium-99 last?

Technetium-99 has a half-life of 211,100 years in the IAEA's evaluation, 2.1 × 10⁵ years according to Los Alamos and 210,000 years in EPA's figure. It decays wholly by beta-minus emission, the release of an electron from the nucleus, in IAEA's data. That long half-life keeps it in the environment for an extended period, EPA notes. Technetium-99m, by contrast, lasts about six hours and leaves the body quickly.