Beryllium vs Magnesium
Beryllium and Magnesium sit in the same column of the periodic table — same family, one period apart — so almost every difference between them comes from one thing: the extra electron shell Magnesium wears.
Side by side
| Property | Beryllium | Magnesium |
|---|---|---|
| Symbol | Be | Mg |
| Atomic number (Z) | 4 | 12 |
| Atomic mass | 9.0122 u | 24.305 u |
| Category | Alkaline earth metal | Alkaline earth metal |
| Group | 2 | 2 |
| Period | 2 | 3 |
| Phase at room temp | solid | solid |
| Electron configuration | [He] 2s^2 | [Ne] 3s^2 |
| Valence electrons | 2 | 2 |
| Atomic radius | 112 pm | 145 pm |
| Electronegativity | 1.57 | 1.31 |
| First ionisation energy | 900 kJ/mol | 738 kJ/mol |
The verdicts
- Bigger atom: Magnesium — the lower an element sits in its group, the more shells it wears.
- Greedy electron-taker: Beryllium — higher electronegativity means it pulls shared electrons harder.
- Heavier: Magnesium — 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.