Pm
Promethium
Element 61 · Lanthanide
Promethium (Pm)
Promethium is a radioactive rare-earth element with no stable isotopes. Almost all of it is made in nuclear reactors.
- Lanthanide
- Period 6
- f-block series
- f-block
- solid at room temperature
- ☢ Radioactive
Key properties
- Atomic mass
- [145]
- u
- Electron configuration
- [Xe] 4f5 6s2
- Melting point
- 1,041.9 °C
- 1,315 K
- Boiling point
- 2,999.9 °C
- 3,273 K
- Density
- 7.26 g/cm³
- Electronegativity
- 1.13
- Pauling
- Atomic radius
- 236 pm
- van der Waals
- 1st ionisation energy
- 5.55 eV
Compare with every element:Electronegativity chartAtomic radius chartIonisation energy chartDensity chart of the elementsMelting point chartElectron configuration chart
Did you know?
Notable facts about promethium
- 01
It was found among uranium fission products at Oak Ridge.
- 02
Only about half a kilogram of natural promethium exists in Earth’s crust at any time.
- 03
Promethium powered “atomic batteries” in early pacemakers and in space probes.
Applications
What is promethium used for?
- Nuclear batteries
- Luminous paint (historically)
- Thickness gauges
History
Discovery & name origin
Discovered by
Jacob A. Marinsky, Lawrence E. Glendenin, Charles D. Coryell
Year
Where
United States
Name origin
From Prometheus, the Titan who stole fire from the gods.
Atomic structure
Atomic properties
Atomic structure
Atomic properties
- Atomic number
- 61
- Atomic mass
- [145] u
- Group
- Lanthanides (3)
- Period
- 6
- Block
- f-block
- Electron configuration
- [Xe] 4f5 6s2
- Full configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f5
- Electrons per shell
- 2, 8, 18, 23, 8, 2
- Electronegativity (Pauling)
- 1.13
- Electron affinity
- —
- Atomic radius (van der Waals)
- 236 pm
- Stable isotopes
- None — all isotopes are radioactive
Oxidation states
Highlighted: common oxidation states (+3).
Successive ionisation energies
Energy to remove each electron in turn (kJ/mol). Big jumps show where a new, inner shell begins.
- 1st540
- 2nd1,050
- 3rd2,150
- 4th3,970
Physical
Physical properties & colour
Physical
Physical properties & colour
- State at 20 °C
- Solid
- Melting point
- 1,315 K · 1,041.9 °C · 1,907.3 °F
- Boiling point
- 3,273 K · 2,999.9 °C · 5,431.7 °F
- Density
- 7.26 g/cm³
- Molar heat capacity
- —
- Appearance
- Metallic
- CPK model colour
- Copied
The CPK colour is the convention used for this element’s atoms in molecular models.
FAQ
Promethium questions
What is Pm on the periodic table?
Pm is the symbol for promethium, element 61 on the periodic table. It sits in period 6, in the f-block, in the lanthanide category, and has an atomic mass of [145].
What is the atomic number of promethium?
Promethium has atomic number 61, so every promethium atom has 61 protons in its nucleus. Its symbol is Pm and its atomic mass is [145].
Who discovered promethium?
Promethium was discovered by Jacob A. Marinsky, Lawrence E. Glendenin and Charles D. Coryell in 1945 (United States). The name comes from from Prometheus, the Titan who stole fire from the gods.
What is promethium used for?
Promethium is used for: nuclear batteries; luminous paint (historically); thickness gauges.
Is promethium a metal?
Yes. Promethium is a lanthanide, one of the metallic elements.
What is the electron configuration of promethium?
The electron configuration of promethium is [Xe] 4f5 6s2. Its 61 electrons are arranged in shells as 2, 8, 18, 23, 8, 2.