Sodium vs Chlorine
One is desperate to lose an electron, the other desperate to gain one — put them together and you get table salt.
Side by side
| Property | Sodium | Chlorine |
|---|---|---|
| Symbol | Na | Cl |
| Atomic number (Z) | 11 | 17 |
| Atomic mass | 22.990 u | 35.45 u |
| Category | Alkali metal | Halogen |
| Group | 1 | 17 |
| Period | 3 | 3 |
| Phase at room temp | solid | gas |
| Electron configuration | [Ne] 3s^1 | [Ne] 3s^2 3p^5 |
| Valence electrons | 1 | 7 |
| Atomic radius | 190 pm | 79 pm |
| Electronegativity | 0.93 | 3.16 |
| First ionisation energy | 496 kJ/mol | 1251 kJ/mol |
The verdicts
- Bigger atom: Sodium — the lower an element sits in its group, the more shells it wears.
- Greedy electron-taker: Chlorine — higher electronegativity means it pulls shared electrons harder.
- Heavier: Chlorine — 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.