91Pa231.04
Protactinium
ActinidesHeavy, radioactive metals. Most of them are made only in laboratories.
[Rn] 5f² 6d¹ 7s²
- Atomic number
- 91
- Atomic mass
- 231.04
- Protons
- 91
- Neutrons
- 140 (most common)
- Electrons
- 91
- Shells
- 2, 8, 18, 32, 20, 9, 2
- State at 25 °C
- Solid
- Position
- Period 7, f-block
Proton (+)Neutron (0)Electron (−)
Discovered byKasimir Fajans and Oswald Göhring, 1913Lise Meitner: 1 elementOtto Hahn: 1 element
Otto Hahn and Lise Meitner found a longer-lived form in 1918. Its name means “before actinium”, because it decays into actinium.
Did you know?
- It is one of the rarest and most expensive natural elements.
- It is highly toxic and radioactive.
Where it's found
- Uranium ores, in tiny amounts
What it's used for
- Dating ocean sediments
- Research
Try it
There's no safe home experiment for Protactinium. Explore it with the animated atom above instead.