Technetium (Tc)

Technetium was the first element made rather than found, produced in 1937 by bombarding molybdenum with deuterons in Berkeley's cyclotron and named from the Greek for artificial. Every isotope is radioactive and the longest-lived lasts only about 4.2 million years, so any technetium present when the Earth formed decayed away long ago — yet its spectral lines appear clearly in certain red giant stars, which is direct evidence that those stars are manufacturing heavy elements right now. Technetium-99m, with a convenient six-hour half-life and a clean gamma emission, is the most-used medical radioisotope in the world.

Properties

Atomic number

43

Symbol

Tc

Mass number of most stable isotope

[97]

Category

Transition metal

Group

7

Period

5

Block

d-block

Electron configuration

[Kr] 5s² 4d⁵

Electrons per shell

2, 8, 18, 13, 2

Melting point

2,430 K — 2156.8 °C — 3914.3 °F

Boiling point

4,538 K — 4264.9 °C — 7708.7 °F

Density

11 g/cm³

Electronegativity

1.9 (Pauling)

Oxidation states

+7, +6, +4

Discovered

1937 by Carlo Perrier and Emilio Segrè

Electron configuration

Full

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d⁵

Noble gas shorthand

[Kr] 5s² 4d⁵

Shells

K: 2 · L: 8 · M: 18 · N: 13 · O: 2

What it is used for

• Technetium-99m in around 30 million diagnostic scans a year — bone, heart, thyroid
• A remarkably effective corrosion inhibitor for steel in closed systems
• Calibration standards for beta-emission counting

Hazards

• Every isotope is radioactive; technetium-99 is a long-lived beta emitter

No stable isotope exists. The mass given is the mass number of technetium-97, the longest-lived at about 4.21 million years; technetium-98 is nearly as long-lived and some tables quote [98] instead. Trace amounts do occur naturally in uranium ore as a spontaneous fission product, at roughly one part in 10¹².

Neighbours in the table

Group 7

Elements in the same group share their outer electron count, which is why they behave similarly in reactions. Technetium sits in group 7 with manganese, rhenium, bohrium.