Protactinium (Pa)

From Wikipedia, the free encyclopediaProtactinium is a chemical element with symbol Pa and atomic number 91. It is a dense, silvery-gray metal which readily reacts with oxygen, water vapor and inorganic acids. It forms various chemical compounds where protactinium is usually present in the oxidation state +5, but can also assume +4 and even +2 or +3 states.

Protactinium in the periodic table

Atomic number91
Element categoryActinide

Physical properties

Phase at STPSolid
Density15.37 g/cm3
Atomic weight231.036 u
Melting point1841 K
1567.85 °C
2854.13 °F
Boiling point4300 K
4026.85 °C
7280.33 °F

Atomära egenskaper

Electronegativity (Pauling Scale)1.5
Electron affinity53.03 kJ/mol
Ionization energies
1568 kJ/mol

Electron configuration

Electron configuration1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 5f2 6s2 6p6 6d1 7s2
Electrons per shell2, 8, 18, 32, 20, 9, 2


Discovered byOswald Helmuth Göhring
Kazimierz Fajans
Named byOtto Hahn