91 Pa 231.04
Protactinium
Actinide
Protactinium (Pa) is a chemical element with atomic number 91, classified as a actinide. At room temperature it is a solid. It was discovered in 1913 by Kasimir Fajans, Oswald Helmuth Göhring.
Properties
- Atomic number
- 91
- Atomic mass
- 231.04 u
- Category
- Actinide
- Group
- 0
- Period
- 7
- Block
- f-block
- Electron configuration
- [Rn] 5f² 6d¹ 7s²
- Phase at STP
- Solid
- Density
- 15.37 g/cm³
- Melting point
- 1841 K (1567.8 °C)
- Boiling point
- 4300 K (4026.8 °C)
- Electronegativity
- 1.5
- Atomic radius
- 243 pm
- Ionization energy
- 5.89 eV
- Discovery
- 1913 · Kasimir Fajans, Oswald Helmuth Göhring
Common uses
Research only
Did you know?
One of the rarest and most expensive natural elements.