Chemical element · reference page

43Tc

Technetium

Technetium is element 43 (Tc), located in period 5, group 7 and the d block. At room temperature its reference phase is solid. Its electron configuration is [Kr] 4d5 5s2.

Atomic number43

Standard atomic weightNo standard atomic weight

Group7

Period5

Blockd

Electron configuration[Kr] 4d5 5s2

Electronic structure

What controls its chemistry

The d subshell participates in the chemistry of technetium. Transition metals can use electrons of similar energies in bonding, which is why variable oxidation states, coordination compounds and catalytic behaviour are common across the d block.

Its electron configuration, [Kr] 4d5 5s2, should be read together with the oxidation state of the compound: removing electrons changes which d orbitals are occupied and can alter colour, magnetism, bonding and reactivity.

Chemical forms

Compounds, ions and materials

For technetium, important chemical forms include metals and alloys, oxides, halides and coordination compounds. Variable oxidation states are common because s and d electrons have similar energies, and ligands around the metal ion can strongly alter colour, magnetism and reactivity.

Physical behaviour

State and phase changes

The reference phase at room temperature is solid. The listed density is 11 g/cm³. The melting point is 2 429 K (2 156 °C). The boiling point is 4 538 K (4 265 °C). Pressure, purity and crystal structure can shift measured physical properties.

Occurrence and applications

Where technetium is found and used

In practice, technetium is encountered in medical imaging equipment, scientific research and nuclear medicine.

In practice

Examples of real uses

Medical imaging equipment

Technetium is used in imaging agents, detector materials or the high-field magnets and specialised components of imaging systems.

Scientific research

Technetium is produced, isolated or measured mainly to test atomic, nuclear and periodic trends rather than for bulk commercial use.

Nuclear medicine

A suitable technetium radioisotope can be used for imaging or treatment when its radiation type and half-life match the medical task.

Periodic position

What its neighbours tell us

Technetium is in period 5 and group 7. In the neighbourhood shown here, it lies between molybdenum and ruthenium in the same period; manganese is above it and rhenium below it in the same group. These positions make it possible to compare atomic size, ionisation energy and bonding behaviour with nearby elements.

Reference data

Physical and atomic properties

Classificationtransition metal

Phase at room temperatureSolid

Electron shells2 · 8 · 18 · 13 · 2

Density11 g/cm³

Melting point2 429 K (2 156 °C)

Boiling point4 538 K (4 265 °C)

Pauling electronegativity1.9

First ionisation energy687kJ/mol

Electron affinity53 kJ/mol

Values describe the element or neutral atom where applicable. Physical data can depend on allotrope, pressure and measurement conditions.

History

Discovery and identification

The discovery of technetium is associated with Emilio Segrè. Recognition of the element, isolation of a pure sample and assignment of its modern atomic number did not necessarily occur at the same time.

Isotopes and atomic weight

How isotope composition changes the numbers

Technetium has no standard atomic weight. There is no characteristic terrestrial isotopic mixture from which a stable abundance-weighted average can be assigned.

Technetium has no stable isotope. Its isotopes are radioactive, and their half-lives and decay modes become important whenever the element is measured, handled or used.

Safety

Handling and exposure

The hazards associated with technetium depend on chemical form, dose and route of exposure. Pure technetium, its ions and its compounds can have very different biological and environmental effects, so safety data should be checked for the actual substance being handled.