Promethium

Element 61 on the periodic table, symbol Pm, group 3, period 6.

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.

Appearance: metallic

Properties

Atomic Number: 61
Atomic Mass: 145.0000 u
Group: 3
Period: 6
Block: f-block
Category: Lanthanide
State at 25 °C: Solid
Melting Point: 1,315 K · 1,041.9 °C
Boiling Point: 3,273 K · 2,999.9 °C
Density: 7.26 g/cm³
Atomic Radius: 185 pm
Electronegativity: 1.13
Oxidation States: +3
Abundance in Crust: Vanishingly rare
Discovered: 1945
Discovered By: Chien Shiung Wu

Electron Configuration

[Xe] 4f5 6s2

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f5

Ionisation Energies (kJ/mol)

1. 540
2. 1,050
3. 2,150
4. 3,970

Elements near Promethium

Elements in the same group share the number of outer electrons and behave in similar ways. Elements in the same period share a shell, so they change steadily from left to right.