Pa
Protactinium
Atomic number: 91Mass: 231.036 uCategory: Actinide
About Protactinium
Protactinium is a dense, silvery-grey actinide metal which readily reacts with oxygen, water vapour and inorganic acids. It slowly tarnishes in air. It is toxic and radioactive, making it one of the most hazardous elements.
Properties
Period
7
Group
N/A
Block
F
Category
Actinide
Electronegativity
1.50 (Pauling)
Ionization Energy
568 kJ/mol
Melting Point
1841 K (1568°C)
Boiling Point
4300 K (4027°C)
Density
15.37 g/cm³
Oxidation States
+4, +5
Electron Configuration
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶ 5f² 6d¹ 7s²
[Rn] 5f² 6d¹ 7s²
Shell 1:2e⁻
Shell 2:8e⁻
Shell 3:18e⁻
Shell 4:32e⁻
Shell 5:20e⁻
Shell 6:9e⁻
Shell 7:2e⁻
Real-World Uses
Oceanographic research (Pa-231/Th-230 ratio)
Research only
No commercial applications
Dating ocean sediments
Fundamental physics
Fun Fact
Protactinium is one of the rarest and most expensive naturally occurring elements — it's also one of the least studied due to its extreme toxicity and radioactivity!