Fluorine vs Chlorine
Fluorine and Chlorine 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 Chlorine wears.
Side by side
| Property | Fluorine | Chlorine |
|---|---|---|
| Symbol | F | Cl |
| Atomic number (Z) | 9 | 17 |
| Atomic mass | 18.998 u | 35.45 u |
| Category | Halogen | Halogen |
| Group | 17 | 17 |
| Period | 2 | 3 |
| Phase at room temp | gas | gas |
| Electron configuration | [He] 2s^2 2p^5 | [Ne] 3s^2 3p^5 |
| Valence electrons | 7 | 7 |
| Atomic radius | 42 pm | 79 pm |
| Electronegativity | 3.98 | 3.16 |
| First ionisation energy | 1681 kJ/mol | 1251 kJ/mol |
The verdicts
- Bigger atom: Chlorine — the lower an element sits in its group, the more shells it wears.
- Greedy electron-taker: Fluorine — 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.