Thorium vs Protactinium

Side-by-side comparison of Thorium (Th, element 90) and Protactinium (Pa, element 91) by atomic structure and physical properties.

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PropertyTh Thorium Pa Protactinium
Atomic number9091
SymbolThPa
NameThoriumProtactinium
Categoryactinideactinide
Standard Atomic Weight232.0377 u231.03588 u
Period77
GroupN/AN/A
Blockff
Phase at STPSolidSolid
Electron configuration[Rn]6d27s2[Rn]5f26d17s2
Oxidation states[-1, 1, 2, 3, 4][2, 3, 4, 5]
Electronegativity (Pauling)1.31.5
Electron affinity0.607 eV0.55 eV
Density1.172e+4 kg/m³1.537e+4 kg/m³
Melting point1841.85 °C1571.85 °C
Boiling point4787.85 °CN/A
Discovery year18281913

Key Differences

PropertyTh ThoriumPa Protactinium
Standard Atomic Weight232.0377 u ↑ higher231.03588 u ↓ lower
Density1.172e+4 kg/m³ ↓ lower1.537e+4 kg/m³ ↑ higher
Melting point1841.85 °C ↑ higher1571.85 °C ↓ lower
Electronegativity (Pauling)1.3 ↓ lower1.5 ↑ higher
Electron affinity0.607 eV ↑ higher0.55 eV ↓ lower
Electron configuration[Rn]6d27s2 [Rn]5f26d17s2
Discovery year1828 1913