Protactinium
A rare, dense, radioactive metal with few practical uses.
Inside the Protactinium atom
Switch between Bohr and Quantum Cloud modes to compare a simple teaching model with a more realistic probability-based view, and follow the guided tour to explore the Protactinium atom step by step.
Electron configuration
[Rn] 5f2 6d1 7s2
A neutral Protactinium atom has 91 electrons (equal to its proton count). Choosing a different isotope above changes only the neutron count.
Shell distribution
Electrons fill inner shells before outer ones; the outermost (valence) shell drives the element's chemistry.
Physical & atomic properties
- State (room temp)
- Solid
- Melting point
- 1841 K (1568 °C)
- Boiling point
- 4300 K (4027 °C)
- Density
- 15.37 g/cm³
- Electronegativity
- 1.5 Pauling
- Atomic radius
- 180 pm
- 1st ionization energy
- 568 kJ/mol
- Category
- Actinides
Discovery & naming
- Discovered
- 1913
- Discovered by
- Kazimierz Fajans and Oswald Göhring
- Origin of name
- Greek 'protos', parent of actinium.
Notable uses
Scientific research only.
Where Protactinium comes from
Neutron star mergers
Occurs on Earth only as a fleeting decay product of uranium and thorium, so it inherits their r-process origin.
Simplified origin map — many elements form through more than one astrophysical pathway.
Summary
- Atomic number
- 91
- Atomic mass
- 231.04
- Category
- Actinides
- Group · Period
- — · 7
- Block
- f-block
- Shells
- 2 · 8 · 18 · 32 · 20 · 9 · 2