Guides
Sodium vs Potassium — Property Comparison (which is more reactive?)
Sodium and potassium are both group-1 alkali metals with very similar properties: silvery, soft enough to cut, low density and highly reactive, so they are stored under oil. Their key difference is reactivity — potassium, lower in the same group, is more reactive than sodium.
Data comparison
| Property | Sodium Na | Potassium K |
|---|---|---|
| Atomic number | 11 | 19 |
| Relative atomic mass | 22.99 | 39.10 |
| Configuration | [Ne] 3s¹ | [Ar] 4s¹ |
| Electronegativity (Pauling) | 0.93 | 0.82 |
| Density (g/cm³) | 0.971 | 0.862 |
| Melting point | 370.9 K (97.7 °C) | 336.5 K (63.4 °C) |
| Boiling point | 1156 K | 1032 K |
Reactivity: K > Na
Potassium's outer electron is farther from the nucleus and easier to lose, so it is more reactive than sodium: with water, sodium floats and melts into a ball releasing hydrogen, while potassium reacts more violently and the heat often ignites the hydrogen (lilac flame). That is why K sits above Na in the activity series.
Both follow: 2M + 2H₂O → 2MOH + H₂↑ (M = Na or K).
What they share
- Both are silvery soft metals you can cut with a knife.
- Both oxidize readily and must be stored away from air and water.
- Flame test: sodium yellow, potassium lilac (viewed through blue cobalt glass).
For more numeric comparisons use the comparison tool.