Promethium is a radioactive lanthanide with no assigned standard atomic weight. It can be produced by irradiating other elements or separated from nuclear-reactor processing wastes. Its radiation has been used in specialized measuring devices and power sources, so isotope identity matters when explaining its behavior.
FROM ELEMENT TO APPLICATION
AN ELEMENT IN CONTEXT
How does a promethium nuclear battery differ from a rechargeable chemical battery?
Promethium-147 in a nuclear battery
FOLLOW THIS RELATIONSHIP
Select a radioactive energy source
Promethium-147 supplies energy through radioactive decay. This application depends on a particular isotope rather than the general chemical behavior of promethium metal.
Explore the model (optional)
PmFORM → INTERACTION → CONSEQUENCE
Follow the explanation in either direction. These are authored steps, not a physical clock.
Optional: check your understanding
USE THE EXPLANATION
Which process supplies the energy in this example?
Atomic identity, reference properties and structure models
INTERACTIVE 3D61 visible sites
An electron censusDrag to rotate · scroll or pinch to zoom
[Xe] 4f5 6s2. 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.
Jacob Marinsky, Lawrence Glendenin, and Charles Coryell identified promethium at Oak Ridge in 1945 by separating products of nuclear . Public recognition followed in 1947 after wartime secrecy delayed disclosure. Earlier searches for a normal source had been frustrated by its . The discovery joined nuclear physics to separation chemistry: making new and distinguishing their chemical identity were both necessary parts of the evidence.
1945
Element 61 identified
The Oak Ridge team separated and identified promethium.
1947
Discovery made public
The discovery received public recognition after wartime secrecy.
Promethium has no stable , but tiny natural quantities can be regenerated through nuclear processes in uranium-bearing material. Practical quantities require nuclear production and chemical separation. Its occurrence is therefore a changing balance between production and , not a permanent stock of ancient stable atoms hidden in a conventional .
Promethium belongs chemically among the rare-earth elements, while its nuclei are radioactive. Promethium-147 is a specific isotope used in research and instrumentation. The mass number identifies that isotope; it is not a standard atomic weight. Separating chemical behavior from nuclear decay helps explain why neighboring elements are not interchangeable substitutes.
Each section links its supporting references. Descriptions and diagrams were authored for this atlas. Source checks completed. Source checks dated 2026-09-06.
CITE THIS PAGE
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
1315 K
at standard pressure unless noted
Boiling point in K
3273 K
101.325 kPa
Density in g/cm³
7.26 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
Not recorded
Pauling scale
First ionization energy in kJ/mol
540 kJ/mol
gas-phase neutral atom, ground state
Covalent radius in pm
199 pm
single-bond covalent radius
Common oxidation states
+3
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
1945 CEderived
WHERE IT SITS AMONG ITS NEIGHBORS
Electronegativity across period 6
Cs 0.79 Pauling · Cesium
Electronegativity across period 6. Exact values.
Cs
0.79
Ba
0.89
La
1.1
Ce
1.12
Pr
1.13
Nd
1.14
Sm
1.17
Eu
1.2
Gd
1.2
Tb
1.1
Dy
1.22
Ho
1.23
Er
1.24
Tm
1.25
Yb
1.1
Lu
1.27
Hf
1.3
Ta
1.5
W
2.36
Re
1.9
Os
2.2
Ir
2.2
Pt
2.28
Au
2.54
Hg
2
Tl
1.62
Pb
2.33
Bi
2.02
Po
2
At
2.2
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.
