Element 91
Protactinium (Pa)
Protactinium (Pa) is element 91 of the periodic table, a actinide in period 7 (f-block) with an atomic mass of 231.04 and is a solid at standard conditions.
At a glance
- Atomic number
- 91
- Symbol
- Pa
- Atomic mass
- 231.04 u
- Category
- Actinides
- Period
- 7
- Block
- f-block
- Phase at STP
- solid
Electron structure
- Electron configuration
- 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p6 5f2 6d1 7s2
- Shorthand configuration
- [Rn] 5f2 6d1 7s2
- Electrons per shell
- 2, 8, 18, 32, 20, 9, 2
- Oxidation states
- +2, +3, +4, +5
Physical properties
- Melting point
- 1841 K
- Boiling point
- 4300 K
- Density
- 15.37 g/cm3
- Phase
- solid
Atomic properties
- Electronegativity (Pauling)
- 1.5
- Atomic radius
- 163 pm
- Covalent radius
- 200 pm
- First ionization energy
- 568 kJ/mol
- Electron affinity
- 53 kJ/mol
Notable isotopes
| Isotope | Mass | Abundance | Stability |
|---|---|---|---|
| Pa-231 | 231.03588 | — | Half-life 32760 years |
Common uses
- Scientific research only
Discovery
- Year
- 1913
- Discovered by
- Kasimir Fajans, Oswald Helmuth Göhring
- Country
- Germany