Sodium vs Calcium
One explodes in water, the other builds bones and shells — the liveliest metal of Group 1 against the steady builder of Group 2.
Side by side
| Property | Sodium | Calcium |
|---|---|---|
| Symbol | Na | Ca |
| Atomic number (Z) | 11 | 20 |
| Atomic mass | 22.990 u | 40.078 u |
| Category | Alkali metal | Alkaline earth metal |
| Group | 1 | 2 |
| Period | 3 | 4 |
| Phase at room temp | solid | solid |
| Electron configuration | [Ne] 3s^1 | [Ar] 4s^2 |
| Valence electrons | 1 | 2 |
| Atomic radius | 190 pm | 194 pm |
| Electronegativity | 0.93 | 1 |
| First ionisation energy | 496 kJ/mol | 590 kJ/mol |
The verdicts
- Bigger atom: Calcium — the lower an element sits in its group, the more shells it wears.
- Greedy electron-taker: Calcium — higher electronegativity means it pulls shared electrons harder.
- Heavier: Calcium — compare the atomic masses in the table above.
Want the visual version with bars for radius, electronegativity and ionisation energy? Open the interactive compare tool with this pair already loaded.