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.
Experiment with the elements
Protactinium doesn't form any compounds in our lab yet, but the periodic table sandbox lets you combine dozens of other real elements into real compounds — water, table salt, ammonia and many more — with their true chemical formulas.