Technetium
[Kr] 4d⁵ 5s² · 2 · 8 · 18 · 13 · 2
The first element made artificially by humans, and the lightest with no stable isotope at all. Technetium filled the empty box under manganese that Mendeleev had predicted back in 1871.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 43
- Atomic mass
- 98 а.е.м. ≈
- Electron configuration
- [Kr] 4d⁵ 5s²
- Electrons per shell
- 2 · 8 · 18 · 13 · 2
- Block
- d-block
- Group
- Manganese group
- Period
- 5
- Electronegativity (Pauling)
- 1.9
- Electronegativity (Allen)
- 1.51
- Atomic radius
- 183 pm
- Covalent radius
- 147 pm
- Van der Waals radius
- 209 pm
- Ionisation energy 1
- 702 kJ/mol
- Ionisation energy 2
- 1 470 kJ/mol
- Ionisation energy 3
- 2 850 kJ/mol
- Electron affinity
- 53 kJ/mol
- Common oxidation states
- +4, +7
- Oxidation states
- -3, -1, +1, +2, +3, +4, +5, +6, +7
Physical properties
- State at 25 °C
- solid
- Density
- 11 g/cm³
- Melting point
- 2 430 K · 2 156.9 °C
- Boiling point
- 4 538 K · 4 264.9 °C
- Speed of sound
- no data
Thermal properties
- Heat of fusion
- 33.29 kJ/mol
- Heat of vaporisation
- 585.2 kJ/mol
- Specific heat capacity
- 0.24 J/(g·K)
- Thermal conductivity
- 50.6 W/(m·K)
Mechanical properties
- Young's modulus
- no data
- Shear modulus
- no data
- Bulk modulus
- no data
- Poisson ratio
- no data
- Mohs hardness
- no data
- Brinell hardness
- no data
Electrical and magnetic properties
- Electrical resistivity
- 200 nΩ·m
- Magnetic ordering
- paramagnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- 7.46 K
Crystal structure
- Crystal structure
- hexagonal close-packed (hcp)
- Lattice constants
- a = 273.8 pm · c = 439.3 pm
Abundance
- In the crust
- 0 mg/kg
- In the ocean
- 0 mg/L
- In the universe
- 0 mg/kg
- In the human body
- 0 mg/kg
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 97Tc | — | 4.21 Myr | ЭЗ |
| 98Tc | — | 4.21 Myr | β− |
| 99Tc | — | 211 047 yr | β− |
Technetium-99m is a metastable isomer with a 6-hour half-life; it emits a 140 keV gamma photon perfectly matched to a gamma camera, and no stray beta dose.
Discovery
- Year of discovery
- 1937
- Discovered by
- Carlo Perrier and Emilio Segrè
- Where
- Italy
- Origin of the name
- from Greek technetos (artificial): the first element made by humans
History
Box 43 defeated chemists for decades, with announced discoveries that never held up. In 1937 Perrier and Segrè found the element in a molybdenum strip that had been irradiated with deuterons in Lawrence's cyclotron.
Where it occurs
Essentially absent from Earth; traces form from spontaneous fission of uranium. But technetium lines show up in the spectra of red giants — direct proof of nucleosynthesis happening now.
How it is produced
Recovered from spent nuclear fuel, where technetium-99 is a major fission product. Medical technetium-99m comes from molybdenum-99 generators.
Role in living things
No biological role. The pertechnetate ion behaves like iodide and concentrates in the thyroid, which several diagnostic procedures exploit.
Safety
Technetium-99m emits soft gamma radiation and decays in six hours, which makes it nearly ideal for imaging. Long-lived technetium-99 has to be handled as radioactive waste.
Uses
- Technetium-99m — the most used radiopharmaceutical in the world, about 80 % of all diagnostic isotope studies
- Steel corrosion inhibitors in closed loops (only in shielded systems)
- Reference sources for calibrating radiometric instruments
Curiosities
- The name means artificial — technetium was the first element humans manufactured.
- Finding technetium in stellar spectra proved that heavy elements are being made right now.
- Technetium-99m is used in roughly 30 million medical procedures each year.
- Between stable molybdenum and stable ruthenium, technetium stands as a hole in the table: not one stable isotope.