Chlorine: the essentials
Chlorine is a greenish yellow gas which combines directly with nearly all elements. Chlorine is a respiratory irritant. The gas irritates the mucous membranes and the liquid burns the skin. As little as 3.5 ppm can be detected as an odour, and 1000 ppm is likely to be fatal after a few deep breaths. It was used as a war gas in 1915. It is not found in a free state in nature, but is found commonly as NaCl (solid or seawater).
- Name: chlorine
- Symbol: Cl
- Atomic number: 17
- Relative atomic mass (Ar): 35.453 (2) [see notes g m]
- Standard state: gas at 298 K
- Colour: yellowish green
- Classification: Non-metallic
- Group in periodic table: 17
- Group name: Halogen
- Period in periodic table: 3
- Block in periodic table: p-block
- Electron shell structure: 2.8.7
- CAS Registry ID: 7782-50-5
Chlorine: historical information
Chlorine was discovered in 1774 by Carl Wilhelm Scheele. He obtained it through the reaction of the mineral pyrolusite (manganese dioxide, MnO2) with hydrochloric acid (HCl, then known as muriatic acid). Scheele thought the resulting gas contained oxygen. Sir Humphry Davy proposed and confirmed chlorine to be an element in 1810, and he also named the element.
Chlorine around us Read more »
Chlorine as chloride (Cl-) is essential for mammals and plants. Digestive juices in the stomache contain hydrochloric acid.
Chlorine is never found in nature as the free gas. It is found mainly as rock salt (common salt, halite, NaCl), carnallite (KMgCl3.6H2O), and sylvite (KCl).
| Location | ppb by weight | ppb by atoms | Links |
|---|---|---|---|
| Universe | 1000 | 40 | 
|
| Crustal rocks | 170000 | 100000 | 
|
| Human | 1200000 ppb by weight | 210000 atoms relative to C = 1000000 | 
|
Physical properties Read more »
Density of solid: 2030 kg m-3
Molar volume: |196| cm3
Thermal conductivity: |206| W m‑1 K‑1
Heat properties Read more »
Melting point: 171.6 [‑101.5 °C (‑150.7 °F)] K
Boiling point: 239.11 [‑34.04 °C (‑29.27 °F)] K
Enthalpy of fusion: |203| kJ mol-1
Crystal structure Read more »
The solid state structure of chlorine is: orthorhombic.
Chlorine: orbital properties Read more »
Chlorine atoms have 17 electrons and the shell structure is 2.8.7. The ground state electronic configuration of neutral Chlorine is [Ne].3s2.3p5 and the term symbol of Chlorine is 2P3/2.
Pauling electronegativity: 3.16 (Pauling units)
First ionisation energy: 1251.2 kJ mol‑1
Second ionisation energy: 2298 kJ mol‑1
Isolation
Isolation: it is rarely necessary to make chlorine in the laboratory as it is readily available commercially in cylindes. Chlorine is found largely in seawater where it exists as sodium chloride. It is recovered as a reactive, corrosive, pale green chlorine gas from brine (a solution of sodium chloride in water) by electrolyis. Electrolysis of molten salt, NaCl, also succeeds, in which case the other product is sodium metal rather than sodium hydroxide.
Na+ + Cl- + H2O → Na+ + 1/2Cl2 + 1/2H2 + OH-
In the laboratory under carefully controlled conditions, chlorine can be made by the action of an oxidizing agent such as manganese dioxide, MnO2, upon concentrated hydrochloric acid - the same reaction used by Scheele in 1774 when discovering chlorine.
MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O
Chlorine isotopes Read more »
Both Chlorine isotopes, Cl-35 and Cl-37, are used to study the toxicity of environmental pollutant and are usually supplied in the form of NaCl.
| Isotope | Mass /Da |
Natural abund. (atom %) |
Nuclear spin (I) |
Nuclear magnetic moment (μ/μN) |
|---|---|---|---|---|
| 35Cl | 34.968852721 (69) | 75.78 (4) | 3/2 | 0.8218736 |
| 37Cl | 36.96590262 (11) | 24.22 (4) | 3/2 | 0.6841230 |
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