Pa
Protactinium
Z 91 231.036 g/molActinide Radioactive
Nucleus
91 Protons
140 Neutrons
91 Electrons (5 Valence)
Shell distribution: K2 • L8 • M18 • N32 • O20 • P9 • Q2
Electron Configuration
Energy
7p
6d
5f
7s
6p
5d
4f
6s
5p
4d
5s
4p
3d
4s
3p
3s
2p
2s
1s
[Rn]5f26d17s2
Oxidation States
CommonRare
0
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Radii
Empirical
180 pm1.8 Å
Calculated
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Covalent
200 pm2 Å
Van der Waals
243 pm2.43 Å
IonicPa5+
78 pm0.78 Å
Crystal Structure
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TetragonalStandard state
Pearson symbol
tI2
Space group
I4/mmm No. 139
Density
15.37 g/cm³