Technetium has no assigned standard atomic weight in the CIAAW table. Its radioactive isotope technetium-99m is widely used in diagnostic imaging, with different chemical forms directing it to different parts of the body. Technetium is also recovered from products of nuclear-fuel fission.
FROM ELEMENT TO APPLICATION
AN ELEMENT IN CONTEXT
How do the compound and technetium isotope perform different imaging jobs?
Technetium-99m in formulated radiopharmaceutical compounds
FOLLOW THIS RELATIONSHIP
Give the tracer chemical context
A professionally prepared compound carries technetium-99m in a particular chemical formulation. That formulation influences the tracer’s distribution within the investigated system.
Explore the model (optional)
TcFORM → INTERACTION → CONSEQUENCE
Follow the explanation in either direction. These are authored steps, not a physical clock.
Optional: check your understanding
USE THE EXPLANATION
Two formulations contain the same isotope. Must their recorded distributions be identical?
Atomic identity, reference properties and structure models
INTERACTIVE 3D43 visible sites
An electron censusDrag to rotate · scroll or pinch to zoom
[Kr] 4d5 5s2. Grouping electrons by principal shell connects the neutral-atom configuration to periodic-table patterns.
What this representation means
A three-dimensional counting diagram. Dots are count markers, not measured electron positions; spherical placement and spacing are arbitrary. There are no electron trajectories here. Orbitals describe quantum states.
Carlo Perrier and Emilio Segrè identified technetium in 1937 while studying molybdenum exposed in a cyclotron. Their work filled the periodic-table position at atomic number 43 through nuclear production rather than a conventional separation. They proposed the name technetium in 1947. Discovery by synthesis does not mean absolute absence from nature: tiny quantities can be replenished by natural nuclear processes.
1937
Element 43 identified
Perrier and Segrè investigated irradiated molybdenum.
1947
Name proposed
Their published naming proposal introduced technetium.
All technetium are radioactive, so ancient supplies have not simply persisted unchanged since Earth formed. Trace natural technetium can arise through nuclear processes involving uranium. Practical supplies come from deliberate nuclear production. Here occurrence depends on both chemistry and the balance between formation and radioactive .
Technetium chemistry and technetium answer different questions. Chemical bonding determines the compounds it can form; the isotope determines nuclear decay behavior. Technetium-99m and technetium-99 share an atomic number but represent different nuclear states. Their labels must not be treated as a standard atomic weight or as interchangeable application names.
Each section links its supporting references. Descriptions and diagrams were authored for this atlas. Source checks completed. Source checks dated 2026-09-06.
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Family labels and the group-3 layout are teaching conventions. A table position does not establish an unknown bulk property. Electronic configurations refer to neutral atoms; ions and material environments require their own account.
Read each reference property together with its units, conditions and the reference information below.
Not yet recorded: electron affinity, second ionization energy, ground-state term symbol, van der waals radius, thermal conductivity, specific heat capacity, electrical resistivity, crystal structure, lattice parameter a, space group, abundance in seawater, abundance in the universe, annual production, supply-risk listing, hazard classification, biological role, cas registry number, pubchem cid, wikidata item. These families are declared and awaiting an ingestion run against the source each names; they are listed here rather than shown as empty rows.
Physical
Intended reference: CRC Handbook of Chemistry and Physics · CRC Press
Phase at 20 °C
solid
293.15 K, 101.325 kPa
Melting point in K
2430 K
at standard pressure unless noted
Boiling point in K
4538 K
101.325 kPa
Density in g/cm³
11 g/cm³
solids and liquids at 293 K; gases at 273 K and 101.325 kPa
Atomic and electronic
Intended reference: Pauling electronegativity scale · Widely tabulated; original in The Nature of the Chemical Bond
Electronegativity in Pauling
1.9 Pauling
Pauling scale
First ionization energy in kJ/mol
702 kJ/mol
gas-phase neutral atom, ground state
Covalent radius in pm
147 pm
single-bond covalent radius
Common oxidation states
+4, +7
states met in ordinary compounds; not exhaustive
Occurrence and identity
Intended reference: CRC Handbook of Chemistry and Physics · CRC Press
Abundance in the crust
Not recorded
upper continental crust, mass fraction
Has stable isotopes
Noderived
Discovery year in CE
1937 CEderived
WHERE IT SITS AMONG ITS NEIGHBORS
Electronegativity across period 5
Tc 1.9 Pauling · Technetium
Electronegativity across period 5. Exact values.
Rb
0.82
Sr
0.95
Y
1.22
Zr
1.33
Nb
1.6
Mo
2.16
Tc
1.9
Ru
2.2
Rh
2.28
Pd
2.2
Ag
1.93
Cd
1.69
In
1.78
Sn
1.96
Sb
2.05
Te
2.1
I
2.66
Xe
2.6
Electronegativity down group 7
Tc 1.9 Pauling · Technetium
Electronegativity down group 7. Exact values.
Mn
1.55
Tc
1.9
Re
1.9
The trend uses the same reference-property values as the periodic table. Elements with no recorded value are left out of the line rather than drawn at zero.
