Chlorine
[Ne] 3s² 3p⁵ · 2 · 8 · 7
A yellow-green poisonous gas that, bound, turns out to be table salt. Chlorinating water has saved more lives than almost any other public-health measure, and the same gas became the first weapon of mass chemical warfare.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 17
- Atomic mass
- 35.45 а.е.м.
- Electron configuration
- [Ne] 3s² 3p⁵
- Electrons per shell
- 2 · 8 · 7
- Block
- p-block
- Group
- Halogens
- Period
- 3
- Electronegativity (Pauling)
- 3.16
- Electronegativity (Allen)
- 2.87
- Atomic radius
- 79 pm
- Covalent radius
- 102 pm
- Van der Waals radius
- 175 pm
- Ionisation energy 1
- 1 251.2 kJ/mol
- Ionisation energy 2
- 2 298 kJ/mol
- Ionisation energy 3
- 3 822 kJ/mol
- Ionisation energy 4
- 5 158.6 kJ/mol
- Ionisation energy 5
- 6 542 kJ/mol
- Electron affinity
- 349 kJ/mol
- Common oxidation states
- -1, +1, +5, +7
- Oxidation states
- -1, +1, +2, +3, +4, +5, +6, +7
Physical properties
- State at 25 °C
- gas
- Density
- 0.00321 g/cm³
- Melting point
- 171.6 K · -101.6 °C
- Boiling point
- 239.11 K · -34 °C
- Speed of sound
- 206 m/s
Thermal properties
- Heat of fusion
- 6.406 kJ/mol
- Heat of vaporisation
- 20.41 kJ/mol
- Specific heat capacity
- 0.479 J/(g·K)
- Thermal conductivity
- 0.0089 W/(m·K)
Mechanical properties
- Young's modulus
- no data
- Shear modulus
- no data
- Bulk modulus
- 1.1 GPa
- Poisson ratio
- no data
- Mohs hardness
- no data
- Brinell hardness
- no data
Electrical and magnetic properties
- Electrical resistivity
- no data
- Magnetic ordering
- diamagnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- no data
Crystal structure
- Crystal structure
- orthorhombic
- Lattice constants
- a = 622.35 pm · b = 445.61 pm · c = 817.85 pm
Abundance
- In the crust
- 145 mg/kg
- In the ocean
- 19 400 mg/L
- In the universe
- 1 000 mg/kg
- In the human body
- 1 200 mg/kg
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 35Cl | 75.76 % | stable | — |
| 36Cl | — | 301 011.33 yr | β− |
| 37Cl | 24.24 % | stable | — |
Chlorine-36, half-life 300 000 years, forms in the atmosphere and dates groundwater up to a million years old.
Discovery
- Year of discovery
- 1774
- Discovered by
- Carl Wilhelm Scheele
- Where
- Sweden
- Origin of the name
- from Greek chloros (yellow-green), the colour of the gas
History
Scheele made chlorine in 1774 by treating pyrolusite with hydrochloric acid, but took it for a compound. Davy proved it an element in 1810 and named it from the Greek for yellow-green.
Where it occurs
145 mg/kg in the crust, but in the ocean chloride is the dominant anion at 19 400 mg per litre. The main mineral is halite, rock salt.
How it is produced
By chloralkali electrolysis of NaCl solution, which also yields caustic soda and hydrogen. The three products are inseparable, so their markets are locked together.
Role in living things
Chloride is the principal extracellular anion, holding osmotic balance and carrying inhibitory nerve signals. Stomach acid is chlorine too.
Safety
Inhaled chlorine causes pulmonary oedema; at 1000 ppm death follows in minutes. Mixing household bleach with acidic cleaners releases chlorine, a common domestic poisoning.
Uses
- Disinfecting drinking water and swimming pools
- PVC production — chlorine's largest chemical use
- Bleaching pulp and textiles
- Synthesis of solvents, refrigerants and drugs: about a third of all pharmaceutical actives contain chlorine
Curiosities
- Chlorine was first used as a weapon at Ypres in 1915, opening the history of chemical warfare.
- Chlorine's atomic mass of 35.45 is a weighted average of two isotopes, not the mass of any one atom.
- PVC is 57 % chlorine by mass, not petroleum.
- The swimming-pool smell is not chlorine but chloramines, its reaction products with organic matter.