Why does Technetium have no stable isotopes?

Technetium has an odd atomic number (43) with a nucleus that cannot reach a stable proton-to-neutron ratio. Nuclear physics predicts — and experiment confirms — that all its isotopes are radioactive, with Tc-98 having the longest half-life of about 4.2 million years.

What is Tc-99m used for?

Technetium-99m (a metastable nuclear isomer) is the most widely used radiotracer in diagnostic nuclear medicine. It emits a 140 keV gamma ray ideal for gamma camera imaging, has a convenient 6-hour half-life, and can be chemically tagged to many biological molecules to image bone, heart, brain, and other organs.

How was Technetium first produced?

In 1937, Carlo Perrier and Emilio Segre at the University of Palermo irradiated a molybdenum foil with deuterons accelerated in Ernest Lawrence's cyclotron at Berkeley. They isolated the new element chemically and published its identification, filling the gap at Z=43 in the periodic table.

Does Technetium occur naturally on Earth?

Only in vanishingly small trace amounts. Fission of uranium in natural nuclear reactors (like the ancient Oklo reactor in Gabon) and spontaneous fission in uranium ores produce minute quantities of Tc, but none persists in significant amounts due to radioactive decay. Commercially, Tc is recovered as a fission product from spent nuclear fuel.

What is the electron configuration of Technetium?

Tc ground-state electron configuration is [Kr] 4d5 5s2 — a half-filled 4d subshell. This gives it multiple accessible oxidation states from -1 to +7, with +4 and +7 being most common in compounds.

Technetium Element Properties

Look up every key property of Technetium (Tc, Z=43): atomic data, physical constants, electron configuration, oxidation states, and discovery history — all in one reference card.

43 Tc 97.91

Technetium

Transition metal • Period 5 • Group 7 • d-block

Atomic Number

Atomic Mass

97.91 u

Symbol

Block

d-block

Period / Group

5 / VII

State at STP

Solid

Full Name	Technetium	The element's IUPAC name
Latin Name	Technetium	From Greek technetos (artificial)
Symbol	Tc	Standard chemical symbol
Atomic Number (Z)	43	Number of protons in the nucleus
Isotopic Mass (Tc-98)	97.9072(3) u	Longest-lived isotope; no standard atomic weight is assigned
CAS Number	7440-26-8	Chemical Abstracts Service registry number
Classification	Transition metal	Element category in the periodic table
Radioactivity	All isotopes radioactive	No stable isotopes exist; lightest such element
Longest-Lived Isotope	Tc-98 (t½ ≈ 4.2 My)	My = million years
Medical Isotope	Tc-99m (t½ = 6.01 h)	Most widely used diagnostic radiotracer in nuclear medicine

Phase at STP	Solid	Standard temperature and pressure (0 °C, 1 atm)
Appearance	Shiny silvery-gray metal	Lustrous appearance similar to platinum
Density	11.5 g/cm³	At room temperature
Melting Point	2157 °C (2430 K)	Temperature at which solid Tc becomes liquid
Boiling Point	4262 °C (4535 K)	Temperature at which liquid Tc becomes gas
Crystal Structure	Hexagonal close-packed (hcp)	Lattice a = 2.738 Å, c = 4.391 Å
Heat of Fusion	33.29 kJ/mol	Enthalpy required to melt one mole of Tc
Heat of Vaporization	585.2 kJ/mol	Enthalpy required to vaporize one mole of Tc
Atomic Radius	136 pm (empirical)	Approximate radius of a neutral Tc atom
Covalent Radius	147 pm	Half the distance between two bonded Tc atoms
Electronegativity	1.90 (Pauling)	Tendency to attract electrons in a bond
Electrical Resistivity	200 nΩ·m (at 20 °C)	Tc is a superconductor below 7.46 K

Electron Configuration

[Kr] 4d⁵ 5s²

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

Oxidation States

+7	Pertechnetate ion (TcO₄^-) — most stable oxidized form; basis for Tc-99m radiopharmaceuticals
+4	TcO₂ and TcCl₄; common oxidation state in reductive environments
+6	TcF₆; high-valent fluoride complex
+5	Tc(V) complexes used as radiopharmaceutical cores (e.g., Tc-DMSA)
+3, +2, +1	Lower states in organometallic and carbonyl complexes
-1	Rare; found in some low-valent carbonyl species

Electrons per Shell	2, 8, 18, 13, 2	K, L, M, N, O shells
Valence Electrons	7	4d⁵ 5s² contributes 7 valence electrons
1st Ionization Energy	702 kJ/mol	Energy to remove the outermost electron
2nd Ionization Energy	1470 kJ/mol	Energy to remove the second electron
3rd Ionization Energy	2850 kJ/mol	Energy to remove the third electron
Superconducting Tc	7.46 K	Critical temperature for superconductivity

Discovery Year	1937	First artificially produced element
Discoverers	Carlo Perrier & Emilio Segre	University of Palermo, Italy
Discovery Method	Cyclotron deuteron bombardment of Mo-96	Lawrence's cyclotron at Berkeley provided the beam
Name Origin	Greek: technetos (artificial)	First element not found in nature but made synthetically
Predicted By	Dmitri Mendeleev, 1871	Called "eka-manganese"; gap at Z=43 in the periodic table
False Claims	Masurium (1925, Noddack et al.)	Disputed claim later determined to be an artifact
Nuclear Medicine	Tc-99m introduced clinically ~1964	Powell Richards and colleagues at Brookhaven National Lab
Production Today	Fission byproduct of nuclear reactors	~1 kg per ton of spent uranium fuel; also via Mo-99 decay for Tc-99m

Key Milestones

1871
Mendeleev predicts "eka-manganese" at Z=43 as a gap in his periodic table.
1925
Walter and Ida Noddack claim discovery of "masurium" — later disproved.
1937
Perrier and Segre isolate Tc from cyclotron-bombarded Mo foil; first confirmed synthetic element.
1952
Technetium detected in red giant stars by Paul Merrill — confirming ongoing stellar nucleosynthesis.
1964
Tc-99m enters clinical nuclear medicine; now used in ~40 million procedures per year worldwide.

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Summary

Technetium (symbol Tc, atomic number 43) is a silvery-gray transition metal and the lightest element with no stable isotopes — all are radioactive. It was the first element to be produced artificially, isolated in 1937 by Carlo Perrier and Emilio Segre from molybdenum bombarded with deuterons. Its most important isotope, Tc-99m, is widely used in nuclear medicine imaging.

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Last updated: 2026-09-30 · Reviewed by Nham Vu