Chlorine (Cl)
Chlorine (Cl) is element 17, a halogen. Atomic mass 35.45, configuration [Ne] 3s² 3p⁵. Properties, isotopes, oxidation states, uses and history, with an interactive 3D atom model.
Key facts
| Atomic number | 17 |
|---|---|
| Symbol | Cl |
| Standard atomic weight | [35.446,35.457] |
| Category | Halogen |
| Group | 17 |
| Period | 3 |
| State at room temperature | Gas |
| Electron configuration | [Ne] 3s² 3p⁵ |
| Valence electrons | 7 |
| Common oxidation states | -1, +1, +3, +5, +7 |
| Common ions | Cl⁻ |
| Electronegativity (Pauling) | 3.16 |
| First ionization energy | 1251 kJ/mol |
| Electron affinity | 348.6 kJ/mol |
| Atomic radius | 79 pm |
| Density | 2.898 g/L |
| Melting point | -100.9°C |
| Boiling point | -34.04°C |
| Specific heat | 0.479 J/(g·°C) |
Natural isotopes
- Cl-35: Stable (75.8%)
- Cl-37: Stable (24.2%)
Common uses
- PVC (Plastics)
- Bleach
- Water purification
Where it matters
- Public Health (Water chlorination/Disinfection)
- Chemical Warfare (WWI Choking gas)
Hazards
- Highly toxic gas
- Pulmonary irritant
History
| Discovered | 1774 |
|---|---|
| Discovered by | Carl Wilhelm Scheele |
| Name | Humphry Davy (from Greek chloros) |