61
Pm
Promethium
145
Promethium (Pm)
LanthanidePeriod 6f-block-blockRadioactive
Promethium, originally prometheum, is a chemical element with the symbol Pm and atomic number 61. All of its isotopes are radioactive; it is one of only two such elements that are followed in the periodic table by elements with stable forms, a distinction shared with technetium. Chemically, promethium is a lanthanide, which forms salts when combined with other elements.
Latin name: Promethium
Atomic Number
61
Atomic Mass
145 g/mol
Phase (STP)
Solid
Electron Config.
[Xe] 4f⁵ 6s²
General
SymbolPm
Atomic Number61
Atomic Mass145 g/mol
CategoryLanthanide
Period6
Blockf-block
Electron Configuration[Xe] 4f⁵ 6s²
Valence Electrons5
Coloursilvery-metallic
Appearancemetallic
CAS NumberCAS7440-12-2
Physical Properties
Phase (STP)Solid
Density7.26 g/cm³
Melting Point1041.85°C · 1907.33°F · 1315.00 K
Boiling Point2999.85°C · 5431.73°F · 3273.00 K
Atomic Properties
Atomic Radius236 pm
Electronegativity1.13 Pauling
Ionization Energy540 kJ/mol
Oxidation States+3
Ion ChargePm3+
Crystal Structure
Crystal Structurehexagonal close-packed
Nuclear & Hazards
RadioactiveYes
Half-life17.7 years (Pm-145)
Abundance
In Universe0.0000000001%
In Earth's Crust0.00000000000001%
Discovery & History
Discovery Year1945
Discovered ByJacob A. Marinsky, Lawrence E. Glendenin, Charles D. Coryell
Country of DiscoveryUSA
Named ByIsotopes of promethium
Isotopes of Promethium
| Isotope | Abundance | Half-life | Decay |
|---|---|---|---|
| Pm-145 | — | 17.7 years | EC, α |
| Pm-146 | — | 5.53 years | EC, β⁻ |
| Pm-147 | — | 2.6234 years | β⁻ |