| Er | Erbium | Rare Earth |
| Atomic number: | 68 | Atomic weight: | 167.26 | ||
| Shells: | 2,8,18,30,8,2 | Orbitals: | [Xe] 4f12 6s2 | ||
| Melting point: | 1529°C | Boiling point: | 2868°C | ||
| Covalent radius: | 1.57 | Å | Atomic volume: | 18.4 | cm³/mol |
| Atomic radius: | 2.45 | Å | Ionic radius: | 1.00 (+3) | Å |
| Electronegativity: | 1.24 | Oxidation states: | |||
| 1st ionization pot.: | 6.1078 | V | 2nd ionization pot.: | 11.929 | V |
| 3rd ionization pot.: | 22.739 | V | Specific heat: | 0.17 | J/gK |
| Heat of fusion: | 19.90 | kJ/mol | Heat of vapor.: | 261.0 | kJ/mol |
| Thermal conduct.: | 0.143 | W/cmK | Electrical conduct.: | 0.0117 | 10^6/cm ohm |
| Density: | 9.05 | g/cm³ | Valence: | 3 |