Fermium vs Mendelevium

Side-by-side comparison of Fermium (Fm, element 100) and Mendelevium (Md, element 101) by atomic structure and physical properties.

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PropertyFm Fermium Md Mendelevium
Atomic number100101
SymbolFmMd
NameFermiumMendelevium
Categoryactinideactinide
Standard Atomic Weight257 u258 u
Period77
GroupN/AN/A
Blockff
Phase at STPSolidSolid
Electron configuration[Rn]5f127s2[Rn]5f137s2
Oxidation states[2, 3][2, 3]
Electronegativity (Pauling)1.31.3
Electron affinity0.35 eV0.98 eV
Density9700 kg/m³1.03e+4 kg/m³
Melting point1526.85 °C826.85 °C
Boiling pointN/AN/A
Discovery year19521955

Key Differences

PropertyFm FermiumMd Mendelevium
Standard Atomic Weight257 u ↓ lower258 u ↑ higher
Density9700 kg/m³ ↓ lower1.03e+4 kg/m³ ↑ higher
Melting point1526.85 °C ↑ higher826.85 °C ↓ lower
Electron affinity0.35 eV ↓ lower0.98 eV ↑ higher
Electron configuration[Rn]5f127s2 [Rn]5f137s2
Discovery year1952 1955