061Lanthanide · Group 3 · Period 6

Promethium

Promethium (Pm) is element 61, a lanthanide in the f-block — group 3, period 6. It is a solid at room temperature with 6 electron shells (2, 8, 18, 23, 8, 2) and an atomic mass of 145 u.

Atomic mass: 145.0 u
Phase · STP: solid
Melting: 1315 K · 1042 °C
Boiling: 3273 K · 3000 °C
Electronegativity: 1.13
Density: 7.26 g/cm³

Identity

Atomic number: 61
Standard atomic weight: 145.0 u
Category: Lanthanide
Group: 3
Period: 6
Block: f-block
Oxidation states: +3

Physical properties

Melting point: 1315 K · 1042 °C
Boiling point: 3273 K · 3000 °C
Density: 7.26 g/cm³
Molar heat capacity: —
Atomic radius: 236 pm
Electron affinity: 12.45 kJ/mol

Atomic structure

61protons

84neutrons

61electrons

2valence e⁻

Noble-gas notation: [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

Periodic trends

Where Promethium ranks across all 118 elements.

Electronegativity1.13

Ionization energy540 kJ/mol

Electron affinity12.45 kJ/mol

Density7.26 g/cm³

Atomic radius236 pm

Ionization energies

Energy to remove each successive electron (kJ/mol).

540

1.1k

2.1k

4.0k

Successive ionization energies (kJ/mol, log scale).

Discovery

Discovered: 1945
Discovered by: Chien Shiung Wu
Named by: Isotopes of promethium
Appearance: metallic