Technetium (Tc)
Element 43 · Transition metal · atomic mass [98] u · group 7, period 5
Electron shells: 2, 8, 18, 13, 2
Technetium was the first element made artificially, filling a stubborn gap in Mendeleev's table. Every isotope is radioactive, so essentially none survives naturally on Earth.
Technetium-99m is used in tens of millions of medical scans a year, despite the element having no stable form.
- Atomic number
- 43
- Atomic mass
- [98] u
- Electron configuration
- [Kr] 5s² 4d⁵
- Group · period · block
- 7 · 5 · d
- Oxidation states
- +4, +6, +7
- Electronegativity
- 1.9 (Pauling)
- Melting point
- 2,157 °C
- Boiling point
- 4,265 °C
- Density
- 11 g/cm³
- State at 20 °C
- Solid
- Appearance
- Silvery-grey metal
- Discovered
- Carlo Perrier and Emilio Segrè, 1937
43 protons, and 43 electrons when neutral
Mass number of the longest-lived isotope — no standard atomic weight exists
Manganese group
What Technetium is used for
- Technetium-99m medical imaging
- Corrosion inhibitor research
- Nuclear medicine tracers
Atomic structure of Technetium
A neutral technetium atom has 43 protons and 43 electrons. Its most common isotope carries about 55 neutrons, which is where the mass number 98 comes from. Change the neutron count and you have a different isotope of technetium; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 18, 13, 2. In orbital notation that is [Kr] 5s² 4d⁵. As a d-block element its valence count is variable, which is why it can form compounds in several oxidation states.
3D electron orbitals
See where Technetium's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Technetium sits in the periodic table
The d-block. Multiple stable oxidation states give them coloured compounds, catalytic ability and the strength that makes them the working metals of industry.
- Directly above: Manganese — same group, so similar chemistry with a smaller atom.
- Directly below: Rhenium — same group, one shell larger.
- One proton lighter: Molybdenum.
- One proton heavier: Ruthenium.
Discovery and naming
Technetium was discovered by Carlo Perrier and Emilio Segrè in 1937. Its name comes from Greek technetos, "artificial", which is also why its symbol (Tc) does not match its English name.
Every isotope of technetium is radioactive, so it has no standard atomic weight. Periodic tables show the mass number of its longest-lived isotope in square brackets instead.
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Technetium?
Technetium has no stable isotope, so it has no standard atomic weight. Periodic tables instead show 98 in square brackets — the mass number of its longest-lived isotope.
How many protons, neutrons and electrons does Technetium have?
Technetium has 43 protons, because the atomic number is the proton count and that is what makes an atom Technetium at all. A neutral Technetium atom has the same number of electrons, 43. The neutron count varies by isotope; the most common one has about 55, since 98 − 43 = 55.
What is the electron configuration of Technetium?
The electron configuration of Technetium is [Kr] 5s² 4d⁵. Its electrons are arranged 2, 8, 18, 13, 2 across 5 shells.
Is Technetium a metal?
Yes. Technetium is classified as a transition metal, on the metallic side of the table.
What group and period is Technetium in?
Technetium is in group 7 (the manganese group), period 5, in the d-block. The group is its column and the period is its row.
What is the charge of Technetium?
Technetium most commonly forms a 7+ or 4+ ion. Like most transition metals it has several accessible oxidation states, so the charge depends on the compound. Across all its compounds it shows oxidation states of +4, +6, +7.
What is the melting point of Technetium?
Technetium melts at 2,157 °C and boils at 4,265 °C. That puts it in the solids at everyday temperatures.
What is Technetium used for?
Technetium-99m medical imaging, Corrosion inhibitor research, Nuclear medicine tracers. Technetium was the first element made artificially, filling a stubborn gap in Mendeleev's table.
Who discovered Technetium, and where does its name come from?
Technetium (Tc) was discovered by Carlo Perrier and Emilio Segrè in 1937. The name comes from Greek technetos, "artificial".
Is Technetium radioactive?
Yes. Every isotope of Technetium is radioactive — it has no stable form at all, which is why the periodic table shows its mass in square brackets rather than as a standard atomic weight.