Potassium vs Rubidium
| Property | K Potassium | Rb Rubidium |
|---|---|---|
| Atomic number | 19 | 37 |
| Symbol | K | Rb |
| Name | Potassium | Rubidium |
| Category | alkali-metal | alkali-metal |
| Standard Atomic Weight | 39.0983 u | 85.4678 u |
| Period | 4 | 5 |
| Group | 1 | 1 |
| Block | s | s |
| Phase at STP | solid | solid |
| Electron configuration | [Ar]4s1 | [Kr]5s1 |
| Oxidation states | [-1, 1] | [-1, 1] |
| Electronegativity (Pauling) | 0.82 | 0.82 |
| Electron affinity | 0.5014 eV | 0.4859 eV |
| Density | 890 kg/m³ | 1530 kg/m³ |
| Melting point | 63.38 °C | 39.31 °C |
| Boiling point | 758.85 °C | 687.85 °C |
| Discovery year | 1807 | 1861 |