Atomic number 91
Protactinium
Actinide
No photo: here’s why
Protactinium is one of the rarest and most radioactive natural elements - isolated only in tiny research quantities, never something you would meet.
Quick facts
- Atomic mass
- 231.04
- Group
- –
- Period
- 7
- State (STP)
- solid
- Electronegativity
- 1.50
- Common ox. states
- +4, +5
Properties
[Rn] 5f² 6d¹ 7s²
- Ionization energy
- 568.0 kJ/mol
- Electron affinity
- –
- Melting point
- 1845.00 K (1571.8 °C)
- Boiling point
- 4300.00 K (4026.8 °C)
How dangerous is it?
One of the rarest natural elements, strongly radioactive and poisonous, so almost no one outside a few research labs ever meets it.
- RadioactiveImmediate and cumulative
It is a brisk alpha emitter, which is mostly stopped by skin but does serious damage to cells once it is inside the body. (the danger climbs sharply if it is inhaled or swallowed)
Worked with only in sealed gloveboxes by trained crews, with frequent contamination checks.
- ToxicBuilds up over time
It is also chemically poisonous as a heavy metal, adding to the harm if any enters the body.
Kept fully contained so none can be breathed in, swallowed, or touched.
How it bonds· family overview
Protactinium (Pa) is an actinide. Like the lanthanides it tends toward a +3 oxidation state, but the early actinides (Th–Am) routinely access +4, +5, +6, even +7 because the 5f electrons are easier to ionize. Most actinides are radioactive; their "bonding" in school is read off the periodic table, not measured in lab.
