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61Pm145.000
Promethium
LanthanidePromethium, 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.
Phase: SolidAppearance: metallic
2, 8, 18, 23, 8, 2
Physical Properties
Atomic Mass145 u
Density7.26 g/cm³
Melting Point1315 K
Boiling Point3273 K
Period6
PhaseSolid
Chemical Properties
Electron Configuration1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f5
Semantic Config[Xe] 4f5 6s2
Shells2, 8, 18, 23, 8, 2
Electron Affinity12.45 kJ/mol
Electronegativity1.13
Ionization Energies
IE1: 540 kJ/molIE2: 1050 kJ/molIE3: 2150 kJ/molIE4: 3970 kJ/mol
Discovery