| Atomic Mass | 35.4527 |
|---|---|
| Electron Configuration | [Ne]3s23p5 |
| Oxidation States | +7, +5, +1, -1 |
| Year Discovered | 1774 |
| Atomic Mass | 35.4527 |
|---|---|
| Electron Configuration | [Ne]3s23p5 |
| Oxidation States | +7, +5, +1, -1 |
| Year Discovered | 1774 |
| Element Name | Chlorine |
|---|---|
| Element Symbol | Cl |
| InChI | InChI=1S/Cl |
| InChIKey | ZAMOUSCENKQFHK-UHFFFAOYSA-N |
| Atomic Weight |
[35.446, 35.457] 35.4527 35.45 [35.446,35.457] |
|---|---|
| Electron Configuration |
[Ne]3s23p5 |
| Atomic Radius |
Van der Waals Atomic Radius : 175 pm (Van der Waals) Empirical Atomic Radius : 100pm (Empirical) Covalent Atomic Radius : 102(4) pm (Covalent) |
| Oxidation States |
+7, +5, +1, -1 7, 6, 5, 4, 3, 2, 1, -1 (a strongly acidic oxide) |
| Ground Level |
2P°3/2 |
| Ionization Energy |
12.968 eV 12.967633 ± 0.000016 eV |
| Electronegativity |
Pauling Scale Electronegativity : 3.16(Pauling Scale) Allen Scale Electronegativity : 2.869(Allen Scale) |
| Electron Affinity |
3.617eV 3.62eV |
| Atomic Spectra |
Lines Holdings Levels Holdings |
| Physical Description |
Gas |
| Element Classification |
Non-metal |
| Element Period Number |
3 |
| Element Group Number |
17 - Halogen |
| Density |
0.003214 grams per cubic centimeter |
| Melting Point |
171.65 K (-101.5°C or -150.7°F) -101.5°C |
| Boiling Point |
239.11 K (-34.04°C or -29.27°F) -34.04°C |
| Estimated Crustal Abundance |
1.45×102 milligrams per kilogram |
| Estimated Oceanic Abundance |
1.94×104 milligrams per liter |
The name derives from the Greek chloros for "pale green" or "greenish yellow" colour of the element. It was discovered by the Swedish pharmacist and chemist Carl-Wilhelm Scheele in 1774. In 1810, the English chemist Humphry Davy proved it was an element.
Since it combines directly with nearly every element, chlorine is never found free in nature. Chlorine was first produced by Carl Wilhelm Scheele, a Swedish chemist, when he combined the mineral pyrolusite (MnO2) with hydrochloric acid (HCl) in 1774. Although Scheele thought the gas produced in his experiment contained oxygen, Sir Humphry Davy proved in 1810 that it was actually a distinct element. Today, most chlorine is produced through the electrolysis of aqueous sodium chloride (NaCl).
From the Greek word chloro, greenish yellow. Discovered in 1774 by Scheele, who thought it contained oxygen. Chlorine was named in 1810 by Davy, who insisted it was an element.
| Year | Atomic Weight (uncertainty) [u] | Reference |
|---|---|---|
| 2009 | [35.446, 35.457] | https://doi.org/10.1351/PAC-REP-10-09-14 |
| 1999 | 35.453(2) | https://doi.org/10.1351/pac200173040667 |
| 1985 | 35.4527(9) | https://doi.org/10.1351/pac198658121677 |
| 1961 | 35.453(1) | https://doi.org/10.1021/ja00881a001 |
| 1925 | 35.457 | https://doi.org/10.1039/CT9252700913 |
| 1909 | 35.46 | https://doi.org/10.1021/ja01931a001 |
| 1902 | 35.45 | https://doi.org/10.1007/BF01370337 |
| Year | Isotope | Abundance (uncertainty) | Reference |
|---|---|---|---|
| 2013 | 35Cl | [0.755, 0.761] | https://doi.org/10.1515/pac-2015-0503 |
| 2013 | 37Cl | [0.239, 0.245] | https://doi.org/10.1515/pac-2015-0503 |
| 2001 | 35Cl | 0.7576(10) | https://doi.org/10.1063/1.1836764 |
| 2001 | 37Cl | 0.2424(10) | https://doi.org/10.1063/1.1836764 |
| 1997 | 35Cl | 0.7578(4) | https://doi.org/10.1351/pac199870010217 |
| 1997 | 35Cl | 0.2422(4) | https://doi.org/10.1351/pac199870010217 |
| 1989 | 35Cl | 0.7577(7) | https://doi.org/10.1351/pac199163070991 |
| 1989 | 37Cl | 0.2423(7) | https://doi.org/10.1351/pac199163070991 |
| 1975 | 35Cl | 0.7577 | https://doi.org/10.1351/pac197647010075 |
| 1975 | 37Cl | 0.2423 | https://doi.org/10.1351/pac197647010075 |
It is a member of the halogen (salt-forming) group of elements and is obtained from chlorides by the action of oxidizing agents and more often by electrolysis; it is a greenish-yellow gas, combining directly with nearly all elements. At 10°C one volume of water dissolves 3.10 volumes of chlorine, at 30°C only 1.77 volumes.
Chlorine is commonly used as an antiseptic and is used to make drinking water safe and to treat swimming pools. Large amounts of chlorine are used in many industrial processes, such as in the production of paper products, plastics, dyes, textiles, medicines, antiseptics, insecticides, solvents and paints.
Two of the most familiar chlorine compounds are sodium chloride (NaCl) and hydrogen chloride (HCl). Sodium chloride, commonly known as table salt, is used to season food and in some industrial processes. Hydrogen chloride, when mixed with water (H2O), forms hydrochloric acid, a strong and commercially important acid. Other chlorine compounds include: chloroform (CHCl3), carbon tetrachloride (CCl4), potassium chloride (KCl), lithium chloride (LiCl), magnesium chloride (MgCl2) and chlorine dioxide (ClO2).
Chlorine is a very dangerous material. Liquid chlorine burns the skin and gaseous chlorine irritates the mucus membranes. Concentrations of the gas as low as 3.5 parts per million can be detected by smell while concentrations of 1000 parts per million can be fatal after a few deep breaths.
Chlorine is widely used in making many everyday products. It is used for producing safe drinking water the world over. Even the smallest water supplies are now usually chlorinated.
It is also extensively used in the production of paper products, dyestuffs, textiles, petroleum products, medicines, antiseptics, insecticides, food, solvents, paints, plastics, and many other consumer products.
Most of the chlorine produced is used in the manufacture of chlorinated compounds for sanitation, pulp bleaching, disinfectants, and textile processing. Further use is in the manufacture of chlorates, chloroform, carbon tetrachloride, and in the extraction of bromine.
Organic chemistry demands much from chlorine, both as an oxidizing agent and in substitution, since it often brings many desired properties in an organic compound when substituted for hydrogen, as in one form of synthetic rubber.
In nature it is found in the combined state only, chiefly with sodium as common salt (NaCl), carnallite, and sylvite.
See more information at the Chlorine compound page.
| CID | Name | Formula | SMILES | Molecular Weight |
|---|---|---|---|---|
| 312 | chloride | Cl- | [Cl-] | 35.45 |
| 5360523 | chlorine | Cl | [Cl] | 35.45 |
| 6857643 | chlorine(1+) | Cl+ | [Cl+] | 35.45 |
| 9877332 | chlorine-36(1-) | Cl- | [36Cl-] | 35.9683068 |
| 10313040 | chlorine-34(1-) | Cl- | [34Cl-] | 33.9737625 |
| 10313043 | chlorine-38(1-) | Cl- | [38Cl-] | 37.968010 |
| 25191441 | chlorine-37(1-) | Cl- | [37Cl-] | 36.9659026 |
| 131873438 | chlorine-36 | Cl | [36Cl] | 35.9683068 |
Chlorine is a respiratory irritant. The gas irritates the mucus membranes and the liquid burns the skin. As little as 3.5 ppm can be detected as an odor, and 1000 ppm is likely to be fatal after a few deep breaths. In fact, chlorine was used as a war gas in 1915.
Exposure to chlorine should not exceed 0.5 ppm (8-hour time-weighted average - 40 hour week).
| Stable Isotope Count | 2 |
|---|
Because molecules, atoms, and ions of the stable isotopes of chlorine possess slightly different physical and chemical properties, they commonly will be fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights. There are substantial variations in the isotopic abundances of chlorine in natural terrestrial materials (Fig. IUPAC.17.1). These variations are useful for investigating the origin of substances and studying environmental, hydrological, and geological processes. Chlorine is subject to isotopic fractionation by physical and chemical processes. Variations in isotopic compositions of stable chlorine isotopes provide evidence for ultrafiltration and crystallization of brines and indicate sources of chlorine-bearing contaminants, such as solvents and rocket fuels, in the environment [151], [152].
![Fig. IUPAC.17.1: Variation in atomic weight with isotopic composition of selected chlorine-bearing materials (modified from [13], [17]).](https://pubchem.ncbi.nlm.nih.gov/images/iupac/j_pac-2015-0703_fig_031.jpg)
Analyses of chlorine isotopes and other environmental tracers can help to identify whether an environmental contaminant is of anthropogenic origin or naturally occurring. For example, perchlorate (ClO4 -) can be of anthropogenic origin and is also found naturally. Perchlorate is a widespread groundwater contaminant that can interfere with hormone production in the thyroid gland by displacing iodide. Both the stable chlorine isotope-amount ratio n(37Cl)/n(35Cl) and the mole fraction of 36Cl, n(36Cl)/n(Cl), can provide useful information about origins of perchlorate in the environment (Fig. IUPAC.17.2). Such information may be important for legal reasons and for remediation of contaminated areas [152], [153].
![Fig. IUPAC.17.2: By analyzing the isotopic composition of chlorine and oxygen in perchlorate in groundwaters of Long Island, NY, sources of perchlorate contamination could be identified [154]. Isotopic compositions indicate that wells in different parts of Long Island were contaminated by different sources. The agriculture source of perchlorate (upper photo) is identified as nitrate fertilizer from Chile, where natural perchlorate-bearing nitrate salt deposits were mined and processed for export. The synthetic source is attributed to contamination from a fireworks disposal area (lower photo). (Image Source: J.K. Böhlke, U.S. Geological Survey).](https://pubchem.ncbi.nlm.nih.gov/images/iupac/j_pac-2015-0703_fig_032.jpg)
Radioactive 36Cl provides a useful tool to determine ages in geology and hydrology. Some radioactive 36Cl is cosmogenic and enters the terrestrial environment in precipitation. Because of its long half-life of 3.01×105 years, the level of 36Cl in aquifers can be measured and used to estimate ages (on the order of 105 to 106 years) of old meteoric groundwater (water that was originally precipitation) [155].
Thermonuclear bomb tests in the ocean produced large amounts of 36Cl by neutron reactions with 35Cl in seawater. This was especially prevalent in the late 1950s. Large amounts of this anthropogenic 36Cl were distributed throughout the atmosphere, deposited with precipitation, and incorporated into terrestrial soils and groundwater. This enriched 36Cl has been used as a tracer of meteoric water from that era [156].
| Isotope | Atomic Mass (uncertainty) [u] | Abundance (uncertainty) |
|---|---|---|
| 35Cl | 34.968 8527(3) | [0.755, 0.761] |
| 37Cl | 36.965 9026(4) | [0.239, 0.245] |
| Isotope | Atomic Mass (uncertainty) [u] | Abundance (uncertainty) |
|---|---|---|
| 35Cl | 34.968852682(37) | 0.7576(10) |
| 37Cl | 36.965902602(55) | 0.2424(10) |
| Nuclide | Atomic Mass and Uncertainty [u] | Half Life and Uncertainty | Discovery Year | Decay Modes, Intensities and Uncertainties [%] |
|---|---|---|---|---|
| 28Cl | 28.030349 ± 0.000537 [Estimated] | Not-specified >100ns | 2018 | p=100% |
| 29Cl | 29.015053 ± 0.000203 [Estimated] | 5.4 zs ± 1.9 | 1993 | p=100% |
| 30Cl | 30.005018333 ± 0.000025631 | Not-specified >100ns | 2018 | p=100% |
| 31Cl | 30.992448097 ± 0.0000037 | 190 ms ± 1 | 1977 | β+=100%; β+p=2.4±0.2% |
| 32Cl | 31.985684605 ± 0.000000603 | 298 ms ± 1 | 1953 | β+=100%; β+α=0.054±0.8%; β+p=0.026±0.5% |
| 33Cl | 32.977451988 ± 0.000000419 | 2.5038 s ± 0.0022 | 1940 | β+=100% |
| 34Cl | 33.973762490 ± 0.000000052 | 1.5267 s ± 0.0004 | 1934 | β+=100% |
| 34Clm | 33.973762490 ± 0.000000052 | 31.99 m ± 0.03 | 1965 | β+=55.4±0.6%; IT=44.6±0.6% |
| 35Cl | 34.968852694 ± 0.000000038 | Stable | 1919 | IS=75.8±0.2% |
| 36Cl | 35.968306822 ± 0.000000038 | 301.3 ky ± 1.5 | 1941 | β-=98.1±0.1%; β+=1.9±0.1% |
| 37Cl | 36.965902573 ± 0.000000055 | Stable | 1919 | IS=24.2±0.2% |
| 38Cl | 37.968010408 ± 0.000000105 | 37.230 m ± 0.014 | 1940 | β-=100% |
| 38Clm | 37.968010408 ± 0.000000105 | 715 ms ± 3 | 1954 | IT=100% |
| 39Cl | 38.968008151 ± 0.000001859 | 56.2 m ± 0.6 | 1949 | β-=100% |
| 40Cl | 39.970415466 ± 0.000034423 | 1.35 m ± 0.03 | 1956 | β-=100% |
| 41Cl | 40.970684525 ± 0.000073777 | 38.4 s ± 0.8 | 1971 | β-=100% |
| 42Cl | 41.973342000 ± 0.000064 | 6.8 s ± 0.3 | 1971 | β-=100%; β-n ? |
| 43Cl | 42.974063700 ± 0.000066407 | 3.13 s ± 0.09 | 1976 | β-=100%; β-n ? |
| 44Cl | 43.978014918 ± 0.000091859 | 562 ms ± 106 | 1979 | β-=100%; β-n<8% |
| 45Cl | 44.980394353 ± 0.000146177 | 413 ms ± 25 | 1979 | β-=100%; β-n=24±0.4% |
| 46Cl | 45.985254926 ± 0.0001044 | 232 ms ± 2 | 1989 | β-=100%; β-n=60±0.9%; β-2n ? |
| 47Cl | 46.989715 ± 0.000215 [Estimated] | 101 ms ± 5 | 1989 | β-=100%; β-n<3%; β-2n ? |
| 48Cl | 47.995405 ± 0.000537 [Estimated] | 30 ms >200ns [Estimated] | 1989 | β- ?; β-n ?; β-2n ? |
| 49Cl | 49.000794 ± 0.000429 [Estimated] | 35 ms >200ns [Estimated] | 1989 | β- ?; β-n ?; β-2n ? |
| 50Cl | 50.008266 ± 0.000429 [Estimated] | 10 ms >620ns [Estimated] | 2009 | β- ?; β-n ?; β-2n ? |
| 51Cl | 51.015341 ± 0.000751 [Estimated] | 5 ms >200ns [Estimated] | 1990 | β- ?; β-n ?; β-2n ? |
| 52Cl | 52.024004 ± 0.000751 [Estimated] | 2 ms >400ns [Estimated] | 2018 | β- ?; β-n ?; β-2n ? |
