| Feature | Fluorine (F) | Chlorine (Cl) |
|---|---|---|
| Atomic number | 9 | 17 |
| Period | 2 | 3 |
| Valence orbital | 2p | 3p |
| Orbital size | Very small | Larger |
| Electron–electron repulsion on adding | Very high (compact 2p) | Lower (roomier 3p) |
| EGE value | −328 kJ/mol | −349 kJ/mol |
| More negative EGE? | No | Yes (exception) |
| Electronegativity | 4.0 (highest) | 3.0 |
| 1681 kJ/mol | 1251 kJ/mol | |
| General trend prediction | Should have more negative EGE | Should have less negative EGE |
| Actual behavior | Less negative than Cl | More negative than F (anomaly) |
Conclusion: Fluorine is the most electronegative but NOT the best electron acceptor in terms of enthalpy. The distinction between electronegativity (a relative tendency) and EGE (a measurable energy) is a classic NEET trap.