Einsteinium vs Fermium
Side-by-side comparison of Einsteinium (Es, element 99) and Fermium (Fm, element 100) by atomic structure and physical properties.
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| Atomic number | 99 | 100 |
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| Symbol | Es | Fm |
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| Name | Einsteinium | Fermium |
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| Category | actinide | actinide |
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| Standard Atomic Weight | 252 u | 257 u |
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| Period | 7 | 7 |
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| Group | N/A | N/A |
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| Block | f | f |
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| Phase at STP | Solid | Solid |
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| Electron configuration | [Rn]5f117s2 | [Rn]5f127s2 |
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| Oxidation states | [2, 3, 4] | [2, 3] |
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| Electronegativity (Pauling) | 1.3 | 1.3 |
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| Electron affinity | -0.3 eV | 0.35 eV |
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| Density | 8840 kg/m³ | 9700 kg/m³ |
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| Melting point | 859.85 °C | 1526.85 °C |
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| Boiling point | N/A | N/A |
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| Discovery year | 1952 | 1952 |
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Key Differences
| Es Einsteinium | Fm Fermium |
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| Standard Atomic Weight | 252 u ↓ lower | 257 u ↑ higher |
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| Density | 8840 kg/m³ ↓ lower | 9700 kg/m³ ↑ higher |
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| Melting point | 859.85 °C ↓ lower | 1526.85 °C ↑ higher |
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| Electron affinity | -0.3 eV ↓ lower | 0.35 eV ↑ higher |
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| Electron configuration | [Rn]5f117s2 | [Rn]5f127s2 |
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