| Attribute | Selenium × | Sodium × |
|---|---|---|
| Atomic mass (u) | 78.97 | 22.9897693 |
| Standard state | Solid | Solid |
| Oxidation states |
|
|
| Electron configuration | [Ar]4s²3d¹⁰4p⁴ | [Ne]3s¹ |
| Atomic radius (van der waals) (pm) | 190 | 227 |
| Electronegativity (pauling scale) | 2.55 | 0.93 |
| Electron affinity (eV) | 2.021 | 0.548 |
| Ionization energy (eV) | 9.752 | 5.139 |
| Boiling point (K) | 958 | 1156 |
| Melting point (K) | 493.65 | 370.95 |
| Density (g/cm³) | 4.809 | 0.97 |
| Atomic number | 34 | 11 |
| Group name | Nonmetal | Alkali metal |
| Discovered (year) | 1817 | 1807 |
| Symbol | Se | Na |