Actinium vs Thorium

Side-by-side comparison of Actinium (Ac, element 89) and Thorium (Th, element 90) by atomic structure and physical properties.

← Back to Periodic Table
PropertyAc Actinium Th Thorium
Atomic number8990
SymbolAcTh
NameActiniumThorium
Categoryactinideactinide
Standard Atomic Weight227 u232.0377 u
Period77
GroupN/AN/A
Blockff
Phase at STPSolidSolid
Electron configuration[Rn]6d17s2[Rn]6d27s2
Oxidation states[3][-1, 1, 2, 3, 4]
Electronegativity (Pauling)1.11.3
Electron affinity0.35 eV0.607 eV
Density1.007e+4 kg/m³1.172e+4 kg/m³
Melting point1050.85 °C1841.85 °C
Boiling point3197.85 °C4787.85 °C
Discovery year18991828

Key Differences

PropertyAc ActiniumTh Thorium
Standard Atomic Weight227 u ↓ lower232.0377 u ↑ higher
Density1.007e+4 kg/m³ ↓ lower1.172e+4 kg/m³ ↑ higher
Melting point1050.85 °C ↓ lower1841.85 °C ↑ higher
Boiling point3197.85 °C ↓ lower4787.85 °C ↑ higher
Electronegativity (Pauling)1.1 ↓ lower1.3 ↑ higher
Electron affinity0.35 eV ↓ lower0.607 eV ↑ higher
Electron configuration[Rn]6d17s2 [Rn]6d27s2
Discovery year1899 1828