514
1. General Information
- Symbol: Cl
- Atomic Number: 17
- Atomic Mass: 35.45 u
- Group: 17 (Halogens)
- Period: 3
- Block: p-block
- Electron Configuration: 1s² 2s² 2p⁶ 3s² 3p⁵
- Valence Electrons: 7
- Phase at Room Temperature: Gas
2. Isotopes of Chlorine
| Isotope | Protons | Neutrons | Abundance | Notes |
|---|---|---|---|---|
| ³⁵Cl | 17 | 18 | 75.8% | Most abundant isotope. |
| ³⁷Cl | 17 | 20 | 24.2% | Stable, less common. |
3. Physical Properties
- Color: Yellow-green
- Odor: Pungent, bleach-like smell
- Density: 3.21 g/L (at STP)
- Melting Point: -101.5°C
- Boiling Point: -34.04°C
- State at STP: Gas (diatomic Cl₂)
- Solubility: Slightly soluble in water (forms chlorine water).
4. Chemical Properties
- Highly Reactive Halogen:
- Strong oxidizing agent.
- Combines readily with metals to form salts (e.g., NaCl).
- Toxic and Corrosive:
- Causes irritation to skin, eyes, and lungs.
- Forms Ionic and Covalent Compounds:
- Common oxidation states: -1, +1, +3, +5, +7.
Reaction with Sodium (Salt Formation):
2Na + Cl₂ → 2NaCl
Reaction with Water (Disinfection):
Cl₂ + H₂O → HCl + HOCl (Hypochlorous acid)
Reaction with Hydrogen:
H₂ + Cl₂ → 2HCl
5. Occurrence and Abundance
- 21st most abundant element in Earth’s crust.
- Found in:
- Seawater (NaCl) – Major source.
- Rock Salt (Halite, NaCl).
- Volcanoes and deep-sea vents.
- Atmospheric Presence: Trace amounts.
6. Industrial Production of Chlorine
- Electrolysis of Brine (Chlor-alkali Process):
2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂
- Membrane, diaphragm, and mercury cell methods are used.
7. Uses of Chlorine
| Application | Description |
|---|---|
| Water Treatment | Disinfects drinking water and swimming pools. |
| Bleach Production | Used in sodium hypochlorite (NaClO). |
| PVC Production | Polyvinyl chloride (plastic manufacturing). |
| Pharmaceuticals | Chlorine compounds in drugs and disinfectants. |
| Pesticides and Herbicides | DDT, insecticides, and other agrochemicals. |
| Metallurgy | Extracts metals from ores. |
| Textiles and Paper | Bleaching agent for paper and fabrics. |
| Chemical Manufacturing | Used to produce solvents (e.g., chloroform, CCl₄). |
8. Important Chlorine Compounds
| Compound | Formula | Use |
|---|---|---|
| Sodium Chloride (Table Salt) | NaCl | Essential for life and food. |
| Hydrochloric Acid | HCl | Industrial acid, digestion (stomach). |
| Sodium Hypochlorite | NaClO | Bleach, disinfectant. |
| Chlorine Dioxide | ClO₂ | Water purification. |
| Chloroform | CHCl₃ | Solvent, anesthetic (formerly used). |
| Polyvinyl Chloride (PVC) | (C₂H₃Cl)n | Pipes, cables, and flooring. |
9. Biological Importance of Chlorine
- Essential for Life (as Chloride Ion, Cl⁻):
- Regulates osmotic pressure and acid-base balance in the body.
- Aids in digestion (HCl in stomach acid).
- Chloride ions are necessary for nerve and muscle function.
10. Chlorine in Environmental Chemistry
- Disinfection:
- Used to kill pathogens in drinking water.
- Ozone Depletion:
- Chlorofluorocarbons (CFCs) contribute to ozone layer destruction:
CFCl₃ + UV → Cl + CFCl₂ Cl + O₃ → ClO + O₂
- Chlorofluorocarbons (CFCs) contribute to ozone layer destruction:
- Pollution:
- Chlorine gas leaks pose serious environmental hazards.
11. Safety and Hazards
- Highly Toxic:
- Can cause severe respiratory damage if inhaled.
- Causes skin and eye burns.
- Reactive with Organic Materials:
- Can form toxic chlorinated compounds.
- Fire Risk:
- Combines with hydrogen or hydrocarbons explosively.
Handling Precautions:
- Use in well-ventilated areas.
- Wear protective clothing and masks.
- Store in sealed, corrosion-resistant containers.
Fun Facts About Chlorine:
- Chlorine gas was used in WWI as a chemical weapon.
- Discovered in 1774 by Carl Wilhelm Scheele.
- Chlorine compounds make up 1.9% of ocean mass (mostly as NaCl).
- Bleach (NaClO) uses chlorine as the active ingredient.