Technetium
Atomic Data
| Atomic Number | 43 |
| Symbol | Tc |
| Atomic Weight | 97 u |
| Density (STP) | 11.5 g/cm³ |
| Melting Point | 2156.85 °C (2430 K) |
| Boiling Point | 4264.85 °C (4538 K) |
| Electronegativity | 1.9 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d5 5s2 |
| Oxidation States | +4, +7 |
| Phase at STP | Solid |
| Category | Transition Metal |
| Period / Group | 5 / 7 |
| CAS Number | 7440-26-8 |
Electron Configuration
[Kr] 4d5 5s2
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 6 | 18 |
| M | 3 | 3d | 10 | 28 |
| N | 4 | 4s | 2 | 30 |
| N | 4 | 4p | 6 | 36 |
| N | 4 | 4d | 5 | 41 |
| O | 5 | 5s | 2 | 43 |
| Total | 43 | 43 | ||
Isotopes of Technetium
Technetium has four naturally occurring stable isotopes. The most abundant is ⁹⁷Tc, comprising None% of all naturally occurring Technetium.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Technetium-97 | ⁹⁷Tc | 43 | 54 | trace | Stable |
| Technetium-98 | ⁹⁸Tc | 43 | 55 | trace | Stable |
| Technetium-99 | ⁹⁹Tc | 43 | 56 | trace | Stable |
| Technetium-99 | ⁹⁹Tc | 43 | 56 | trace | Stable |
Abundance & Occurrence
Technetium is present in Earth's crust at approximately trace amounts by mass and at approximately trace amounts by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Radioactivity: all isotopes: Technetium has no stable isotopes; all are radioactive. Tc-99m (t½ = 6 h, gamma emitter) is the most widely used medical radioisotope: medical staff must follow radiation protection procedures and waste disposal regulations.
- Tc-99: long-lived contamination: Tc-99 (t½ = 211,000 years) is a low-energy beta emitter; it is highly mobile in groundwater and is a long-term environmental concern near nuclear waste repositories.
- Handling and containment: All technetium work must be conducted in radiologically controlled areas with appropriate shielding (beta emitter), contamination monitoring, and trained radiation workers.
- Waste disposal: Technetium radioactive waste must be managed according to national nuclear regulatory authority requirements; Tc-99 contamination is particularly difficult to remediate due to its solubility and long half-life.
Technetium in the Real World
Real-World Uses
- Nuclear medicine (SPECT imaging): Technetium-99m (t½ = 6 h) is the most widely used radioisotope in diagnostic nuclear medicine; it is attached to a range of targeting molecules to image bone, heart, kidneys, lungs, and thyroid in single-photon emission CT scans performed on tens of millions of patients annually.
- Corrosion inhibitor research: Pertechnetate ion (TcO₄−) is an effective anodic inhibitor for mild steel in aerated solutions; research interest exists, though the radioactivity of all technetium isotopes limits practical application to closed experimental systems.
- Scientific reference standards: Tc-99 beta sources are used as calibration standards in liquid scintillation counters and as test samples in nuclear fuel cycle and environmental monitoring laboratories studying long-term behaviour of radioactive waste.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
Has technetium ever been used for anything?
Technetium's main use is in nuclear medicine. Technetium-99m (an isomeric state of Tc-99) is the most widely used medical radioisotope in the world, employed in about 30 million diagnostic procedures per year. It is used to image bone, heart, liver, lungs, kidneys, and lymph nodes, because its 6-hour half-life is long enough to complete imaging but short enough to minimise patient radiation dose.
Why is technetium radioactive?
All isotopes of technetium are radioactive because its atomic number (43) sits at a position in the periodic table where no combination of protons and neutrons produces a stable nucleus. This is related to the odd number of protons (43), which makes technetium particularly susceptible to nuclear instability. The most stable isotope, Tc-98, has a half-life of 4.2 million years, so any technetium that existed when Earth formed has long since decayed.
How was technetium discovered?
Technetium was the first element to be produced artificially. It was synthesised in 1937 by Italian physicists Carlo Perrier and Emilio Segrè by bombarding a sample of molybdenum (which had been used as a target in the Berkeley cyclotron) with deuterons. They named it technetium from the Greek 'technetos', meaning artificial. Its discovery filled the gap at atomic number 43 that Mendeleev had predicted.
What is technetium-99m and why is it so useful?
Technetium-99m is a metastable nuclear isomer of technetium-99 that decays by emitting a 140 keV gamma ray with a half-life of about 6 hours. This energy is ideal for detection by gamma cameras. It is produced in hospital radiopharmacies from molybdenum-99 generator systems, decaying from Mo-99 (half-life 66 hours). The 6-hour half-life means imaging must be performed quickly but radiation exposure is limited: making it a practical clinical tool.