Element 1: Hydrogen (H), Other non-metal
Element 2: Helium (He), Noble gas
Element 3: Lithium (Li), Alkali metal
Element 4: Beryllium (Be), Alkaline earth metal
Element 5: Boron (B), Metalloid
Element 6: Carbon (C), Other non-metal
Element 7: Nitrogen (N), Other non-metal
Element 8: Oxygen (O), Other non-metal
Element 9: Fluorine (F), Halogen
Element 10: Neon (Ne), Noble gas
Element 11: Sodium (Na), Alkali metal
Element 12: Magnesium (Mg), Alkaline earth metal
Element 13: Aluminium (Al), Other metal
Element 14: Silicon (Si), Metalloid
Element 15: Phosphorus (P), Other non-metal
Element 16: Sulfur (S), Other non-metal
Element 17: Chlorine (Cl), Halogen
Element 18: Argon (Ar), Noble gas
Element 19: Potassium (K), Alkali metal
Element 20: Calcium (Ca), Alkaline earth metal
Element 21: Scandium (Sc), Transition metal
Element 22: Titanium (Ti), Transition metal
Element 23: Vanadium (V), Transition metal
Element 24: Chromium (Cr), Transition metal
Element 25: Manganese (Mn), Transition metal
Element 26: Iron (Fe), Transition metal
Element 27: Cobalt (Co), Transition metal
Element 28: Nickel (Ni), Transition metal
Element 29: Copper (Cu), Transition metal
Element 30: Zinc (Zn), Transition metal
Element 31: Gallium (Ga), Other metal
Element 32: Germanium (Ge), Metalloid
Element 33: Arsenic (As), Metalloid
Element 34: Selenium (Se), Other non-metal
Element 35: Bromine (Br), Halogen
Element 36: Krypton (Kr), Noble gas
Element 37: Rubidium (Rb), Alkali metal
Element 38: Strontium (Sr), Alkaline earth metal
Element 39: Yttrium (Y), Transition metal
Element 40: Zirconium (Zr), Transition metal
Element 41: Niobium (Nb), Transition metal
Element 42: Molybdenum (Mo), Transition metal
Element 43: Technetium (Tc), Transition metal
Element 44: Ruthenium (Ru), Transition metal
Element 45: Rhodium (Rh), Transition metal
Element 46: Palladium (Pd), Transition metal
Element 47: Silver (Ag), Transition metal
Element 48: Cadmium (Cd), Transition metal
Element 49: Indium (In), Other metal
Element 50: Tin (Sn), Other metal
Element 51: Antimony (Sb), Metalloid
Element 52: Tellurium (Te), Metalloid
Element 53: Iodine (I), Halogen
Element 54: Xenon (Xe), Noble gas
Element 55: Caesium (Cs), Alkali metal
Element 56: Barium (Ba), Alkaline earth metal
Element 57: Lanthanum (La), Lanthanoid
Element 58: Cerium (Ce), Lanthanoid
Element 59: Praseodymium (Pr), Lanthanoid
Element 60: Neodymium (Nd), Lanthanoid
Element 61: Promethium (Pm), Lanthanoid
Element 62: Samarium (Sm), Lanthanoid
Element 63: Europium (Eu), Lanthanoid
Element 64: Gadolinium (Gd), Lanthanoid
Element 65: Terbium (Tb), Lanthanoid
Element 66: Dysprosium (Dy), Lanthanoid
Element 67: Holmium (Ho), Lanthanoid
Element 68: Erbium (Er), Lanthanoid
Element 69: Thulium (Tm), Lanthanoid
Element 70: Ytterbium (Yb), Lanthanoid
Element 71: Lutetium (Lu), Lanthanoid
Element 72: Hafnium (Hf), Transition metal
Element 73: Tantalum (Ta), Transition metal
Element 74: Tungsten (W), Transition metal
Element 75: Rhenium (Re), Transition metal
Element 76: Osmium (Os), Transition metal
Element 77: Iridium (Ir), Transition metal
Element 78: Platinum (Pt), Transition metal
Element 79: Gold (Au), Transition metal
Element 80: Mercury (Hg), Transition metal
Element 81: Thallium (Tl), Other metal
Element 82: Lead (Pb), Other metal
Element 83: Bismuth (Bi), Other metal
Element 84: Polonium (Po), Metalloid
Element 85: Astatine (At), Halogen
Element 86: Radon (Rn), Noble gas
Element 87: Francium (Fr), Alkali metal
Element 88: Radium (Ra), Alkaline earth metal
Element 89: Actinium (Ac), Actinoid
Element 90: Thorium (Th), Actinoid
Element 91: Protactinium (Pa), Actinoid
Element 92: Uranium (U), Actinoid
Element 93: Neptunium (Np), Actinoid
Element 94: Plutonium (Pu), Actinoid
Element 95: Americium (Am), Actinoid
Element 96: Curium (Cm), Actinoid
Element 97: Berkelium (Bk), Actinoid
Element 98: Californium (Cf), Actinoid
Element 99: Einsteinium (Es), Actinoid
Element 100: Fermium (Fm), Actinoid
Element 101: Mendelevium (Md), Actinoid
Element 102: Nobelium (No), Actinoid
Element 103: Lawrencium (Lr), Actinoid
Element 104: Rutherfordium (Rf), Transition metal
Element 105: Dubnium (Db), Transition metal
Element 106: Seaborgium (Sg), Transition metal
Element 107: Bohrium (Bh), Transition metal
Element 108: Hassium (Hs), Transition metal
Element 109: Meitnerium (Mt)
Element 110: Darmstadtium (Ds)
Element 111: Roentgenium (Rg)
Element 112: Copernicium (Cn), Transition metal
Element 113: Ununtrium (Uut)
Element 114: Ununquadium (Uuq)
Element 115: Ununpentium (Uup)
Element 116: Ununhexium (Uuh)
Element 117: Ununseptium (Uus)
Element 118: Ununoctium (Uuo)
Chlorine has a orthorhombic crystal structure
pale yellow-green gas
General properties
Name, symbol, number chlorine, Cl, 17
Pronunciation /ˈklɔərn/ klor-een
Element category halogen
Group, period, block 17, 3, p
Standard atomic weight 35.453(2)
Electron configuration [Ne] 3s2 3p5
Electrons per shell 2, 8, 7 (Image)
Physical properties
Phase gas
Density (0 °C, 101.325 kPa)
3.2 g/L
Liquid density at b.p. 1.5625[1] g·cm−3
Melting point 171.6 K, -101.5 °C, -150.7 °F
Boiling point 239.11 K, -34.04 °C, -29.27 °F
Critical point 416.9 K, 7.991 MPa
Heat of fusion (Cl2) 6.406 kJ·mol−1
Heat of vaporization (Cl2) 20.41 kJ·mol−1
Molar heat capacity (Cl2)
33.949 J·mol−1·K−1
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 128 139 153 170 197 239
Atomic properties
Oxidation states 7, 6, 5, 4, 3, 2, 1, -1
(strongly acidic oxide)
Electronegativity 3.16 (Pauling scale)
Ionization energies
1st: 1251.2 kJ·mol−1
2nd: 2298 kJ·mol−1
3rd: 3822 kJ·mol−1
Covalent radius 102±4 pm
Van der Waals radius 175 pm
Crystal structure orthorhombic
Magnetic ordering diamagnetic[2]
Electrical resistivity (20 °C) > 10 Ω·m
Thermal conductivity 8.9×10−3  W·m−1·K−1
Speed of sound (gas, 0 °C) 206 m·s−1
CAS registry number 7782-50-5
Most stable isotopes
Main article: Isotopes of chlorine
iso NA half-life DM DE (MeV) DP
35Cl 75.77% 35Cl is stable with 18 neutrons
36Cl trace 3.01×105 y β 0.709 36Ar
ε - 36S
37Cl 24.23% 37Cl is stable with 20 neutrons
v ·  /ˈklɔərn/ klohr-een; from Ancient Greek: χλωρóς khlôros "pale green") is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine. It has the highest electron affinity and the third highest electronegativity of all the elements; for this reason, chlorine is a strong oxidizing agent.

The most common compound of chlorine, sodium chloride, has been known since ancient times; however, around 1630, chlorine gas was obtained by the Belgian chemist and physician Jan Baptist van Helmont. The synthesis and characterization of elemental chlorine occurred in 1774 by Swedish chemist Carl Wilhelm Scheele, who called it "dephlogisticated muriatic acid air," having thought he synthesized the oxide obtained from the hydrochloric acid. Because acids were thought at the time to necessarily contain oxygen, a number of chemists, including Claude Berthollet, suggested that Scheele's dephlogisticated muriatic acid air must be a combination of oxygen and the yet undiscovered element, and Scheele named the supposed new element within this oxide as muriaticum. The suggestion that this newly discovered gas was a simple element was made in 1809 by Joseph Louis Gay-Lussac and Louis-Jacques. This was confirmed by Sir Humphry Davy in 1810, who named it chlorine, from the Greek word χλωρος (chlōros), meaning "green-yellow."

Chlorine is a component of various compounds, including table salt. It is the second most abundant halogen and 21st most abundant chemical element in Earth's crust. The great oxidizing potential of chlorine led it to its bleaching and disinfectant uses, as well as uses of an essential reagent in the chemical industry. As a common disinfectant, chlorine compounds are used in swimming pools to keep them clean and sanitary. In the upper atmosphere, chlorine-containing molecules such as chlorofluorocarbons have been implicated in ozone depletion. The elemental chlorine is extremely dangerous and poisonous for all lifeforms; however, chlorine is necessary to most forms of life, including humans, in form of chloride ions.



Physical characteristics

Chlorine, liquefied under a pressure of 8 bar at room temperature. The liquid column size is ca. 0.3×3 cm.

At standard temperature and pressure, two chlorine atoms form the diatomic molecule Cl2.[3] This is a yellow-green gas that has its distinctive strong smell, the smell of bleach.[4] The bonding between the two atoms is relatively weak (only 242.580 ±0.004 kJ/mol), which makes the Cl2 molecule highly reactive. The boiling point at regular atmosphere is around −34 ˚C, but it can be liquefied at room temperature with pressures above 8 atmospheres.[5]

Chemical characteristics

Along with fluorine, bromine, iodine, and astatine, chlorine is a member of the halogen series that forms the group 17 (formerly VII, VIIA, or VIIB) of the periodic table. Chlorine forms compounds with almost all of the elements to give compounds that are usually called chlorides. Chlorine gas reacts with most organic compounds, and will even sluggishly support the combustion of hydrocarbons.[6]


At 25 °C and atmospheric pressure, one liter of water dissolves 3.26 g or 1.02 L of gaseous chlorine.[7] Solutions of chlorine in water contain chlorine (Cl2), hydrochloric acid, and hypochlorous acid:

Cl2 + H2O is in equilibrium with HCl + HClO

This conversion to the right is called disproportionation, because the ingredient chlorine both increases and decreases in formal oxidation state. The solubility of chlorine in water is increased if the water contains dissolved alkali hydroxide, and in this way, chlorine bleach is produced.[8]

Cl2 + 2 OH → ClO + Cl + H2O

Chlorine gas only exists in a neutral or acidic solution.


Chlorine exists in all odd numbered oxidation states from −1 to +7, as well as the elemental state of zero and four in chlorine dioxide (see table below, and also structures in chlorite).[9] Progressing through the states, hydrochloric acid can be oxidized using manganese dioxide, or hydrogen chloride gas oxidized catalytically by air to form elemental chlorine gas.[10]

Name Formula Illustrative compounds
−1 chlorides Cl ionic chlorides, organic chlorides, hydrochloric acid
0 chlorine Cl2 elemental chlorine
+1 hypochlorites ClO sodium hypochlorite, calcium hypochlorite
+3 chlorites ClO
sodium chlorite
+4 chlorine(IV) ClO2 chlorine dioxide
+5 chlorates ClO
sodium chlorate, potassium chlorate, chloric acid
+7 perchlorates ClO
perchloric acid, perchlorate salts such as magnesium perchlorate, dichlorine heptoxide
Chlorine oxides

Chlorine forms a variety of oxides, as seen above: chlorine dioxide (ClO2), dichlorine monoxide (Cl2O), dichlorine hexoxide (Cl2O6), dichlorine heptoxide (Cl2O7). The anionic derivatives of these same oxides are also well known including chlorate (ClO
), chlorite (ClO
), hypochlorite (ClO), and perchlorate (ClO
). The acid derivatives of these anions are hypochlorous acid (HOCl), chloric acid (HClO3) and perchloric acid (HClO4). The chloroxy cation chloryl (ClO2+) is known and has the same structure as chlorite but with a positive charge and chlorine in the +5 oxidation state.[11] The compound "chlorine trioxide", rather than being the expected +6 oxidation state, is instead a mixture of +5 and +7 states, occurring as the ionic compound chloryl perchlorate, [ClO2]+[ClO4] commonly called dichlorine hexoxide.[12]

In hot concentrated alkali solution hypochlorite disproportionates:

2 ClO → Cl + ClO
ClO + ClO
→ Cl + ClO

Sodium chlorate and potassium chlorate can be crystallized from solutions formed by the above reactions. If their crystals are heated, they undergo a further, final disproportionation:

4 ClO
→ Cl + 3 ClO

This same progression from chloride to perchlorate can be accomplished by electrolysis. The anode reaction progression is:[13]

Reaction Electrode
Cl + 2 OH → ClO + H2O + 2 e +0.89 volts
ClO + 2 OHClO
+ H2O + 2 e
+0.67 volts
+ 2 OHClO
+ H2O + 2 e
+0.33 volts
+ 2 OHClO
+ H2O + 2 e
+0.35 volts

Each step is accompanied at the cathode by

2 H2O + 2 e → 2 OH + H2 (−0.83 volts)
Interhalogen compounds

Chlorine oxidizes bromide and iodide salts to bromine and iodine, respectively. However, it cannot oxidize fluoride salts to fluorine. It makes a variety of interhalogen compounds such as the chlorine fluorides, chlorine monofluoride (ClF), chlorine trifluoride (ClF3), chlorine pentafluoride (ClF5). Chlorides of bromine and iodine are also known.[14]

Organochlorine compounds

Chlorine is used extensively in organic chemistry in substitution and addition reactions. Chlorine often imparts many desired properties to an organic compound, in part due to its electronegativity. Some organochlorine compounds are also serious pollutants, either as side products of industrial processes or as persistent pesticides.

Many important industrial products are produced via organochlorine intermediates. Examples include polycarbonates, polyurethanes, silicones, polytetrafluoroethylene, carboxymethyl cellulose, and propylene oxide. Like the other halogens, chlorine participates in free-radical substitution reactions with hydrogen-containing organic compounds. When applied to organic substrates, reaction is often—but not invariably—non-regioselective, and, hence, may result in a mixture of isomeric products. It is often difficult to control the degree of substitution as well, so multiple substitutions are common. If the different reaction products are easily separated, e.g., by distillation, substitutive free-radical chlorination (in some cases accompanied by concurrent thermal dehydrochlorination) may be a useful synthetic route. Industrial examples of this are the production of methyl chloride, methylene chloride, chloroform, and carbon tetrachloride from methane, allyl chloride from propylene, and trichloroethylene, and tetrachloroethylene from 1,2-dichloroethane.

Like the other halides, chlorine undergoes electrophilic addition reactions, the most notable one being the chlorination of alkenes and aromatic compounds with a Lewis acid catalyst. Organic chlorine compounds tend to be less reactive in nucleophilic substitution reactions than the corresponding bromine or iodine derivatives, but they tend to be cheaper. They may be activated for reaction by substituting with a tosylate group, or by the use of a catalytic amount of sodium iodide.[citation needed]


Chlorine combines with almost all elements to give chlorides. Compounds with oxygen, nitrogen, xenon, and krypton are known, but do not form by direct reaction of the elements.[15] Chloride is one of the most common anions in nature. Hydrogen chloride and its aqueous solution, hydrochloric acid, are produced on megaton scale annually both as valued intermediates but sometimes as undesirable pollutants.


In nature, chlorine is found primarily as the chloride ion, a component of the salt that is deposited in the earth or dissolved in the oceans — about 1.9% of the mass of seawater is chloride ions. Even higher concentrations of chloride are found in the Dead Sea and in underground brine deposits. Most chloride salts are soluble in water, thus, chloride-containing minerals are usually only found in abundance in dry climates or deep underground. In the Earth's crust, chlorine is present at average concentrations of about 126 parts per million,[16] predominantly in such minerals as halite (sodium chloride), sylvite (potassium chloride), and carnallite (potassium magnesium chloride hexahydrate). Over 2000 naturally occurring organic chlorine compounds are known.[17]

In the interstellar medium, chlorine is produced in supernovae via the r-process.[18]


Chlorine has a wide range of isotopes. The two stable isotopes are 35Cl (75.77%) and 37Cl (24.23%).[19] Together they give chlorine an atomic weight of 35.4527 g/mol. The half-integer value for chlorine's weight caused some confusion in the early days of chemistry, when it had been postulated that atoms were composed of even units of hydrogen (see Proust's law), and the existence of chemical isotopes was unsuspected.

Trace amounts of radioactive 36Cl exist in the environment, in a ratio of about 7x10−13 to 1 with stable isotopes. 36Cl is produced in the atmosphere by spallation of 36Ar by interactions with cosmic ray protons. In the subsurface environment, 36Cl is generated primarily as a result of neutron capture by 35Cl or muon capture by 40Ca. 36Cl decays to 36S and to 36Ar, with a combined half-life of 308,000 years. The half-life of this hydrophilic nonreactive isotope makes it suitable for geologic dating in the range of 60,000 to 1 million years. Additionally, large amounts of 36Cl were produced by irradiation of seawater during atmospheric detonations of nuclear weapons between 1952 and 1958. The residence time of 36Cl in the atmosphere is about 1 week. Thus, as an event marker of 1950s water in soil and ground water, 36Cl is also useful for dating waters less than 50 years before the present. 36Cl has seen use in other areas of the geological sciences, including dating ice and sediments.[19]


The most common compound of chlorine, sodium chloride, has been known since ancient times; archaeologists have found evidence that rock salt was used as early as 3000 BC and brine as early as 6000 BC.[20] Around 1630, chlorine was recognized as a gas by the Belgian chemist and physician Jan Baptist van Helmont.[21]

Elemental chlorine was first prepared and studied in 1774 by Swedish chemist Carl Wilhelm Scheele, and, therefore, he is credited for its discovery.[22] He called it "dephlogisticated muriatic acid air" since it is a gas (then called "airs") and it came from hydrochloric acid (then known as "muriatic acid").[22] However, he failed to establish chlorine as an element, mistakenly thinking that it was the oxide obtained from the hydrochloric acid (see phlogiston theory). [22] He named the new element within this oxide as muriaticum.[22] Regardless of what he thought, Scheele did isolate chlorine by reacting MnO2 (as the mineral pyrolusite) with HCl:[21]

4 HCl + MnO2 → MnCl2 + 2 H2O + Cl2

Scheele observed several of the properties of chlorine: the bleaching effect on litmus, the deadly effect on insects, the yellow green color, and the smell similar to aqua regia.[23]

At the time, common chemical theory was: any acid is a compound that contains oxygen (still sounding in the German and Dutch names of oxygen: sauerstoff or zuurstof, both translating into English as acid stuff), so a number of chemists, including Claude Berthollet, suggested that Scheele's dephlogisticated muriatic acid air must be a combination of oxygen and the yet undiscovered element, muriaticum.[24][25][26]

In 1809, Joseph Louis Gay-Lussac and Louis-Jacques Thénard tried to decompose dephlogisticated muriatic acid air by reacting it with charcoal to release the free element muriaticum (and carbon dioxide).[22] They did not succeed and published a report in which they considered the possibility that dephlogisticated muriatic acid air is an element, but were not convinced.[27]

In 1810, Sir Humphry Davy tried the same experiment again, and concluded that it is an element, and not a compound.[22] He named this new element as chlorine, from the Greek word χλωρος (chlōros), meaning green-yellow.[28] The name halogen, meaning salt producer, was originally defined for chlorine (in 1811 by Johann Salomo Christoph Schweigger), and later in 1842, at a suggestion by Jöns Jakob Berzelius, this term was applied to the rest of the elements in this family.[29][30] In 1823, Michael Faraday liquefied chlorine for the first time,[31][32] and demonstrated that what was then known as "solid chlorine" had a structure of chlorine hydrate (Cl2·H2O).[21]

Chlorine was first used by Claude Berthollet to bleach textiles in 1785.[33] In 1826, silver chloride was used to produce photographic images for the first time.[34] Chloroform was first used as an anesthetic in 1847.[34] An elemental chlorine solution in water (which was expensive), then the less expensive chlorine gas dissolved in lime-water (calcium hypochlorite) was first used as an antiseptic to prevent the spread of puerperal fever in the maternity wards of Vienna General Hospital in Austria in 1847,.[35] In 1850, chlorine in lime-water was used by John Snow to purify the water supply in London after an outbreak of cholera. (Both uses preceded the germ theory of disease, and were based on destruction of odors and "putrid matter").

The US Department of Treasury called for all water to be disinfected with chlorine by 1918.[34] Polyvinyl chloride (PVC) was invented in 1912, initially without a purpose.[34] Chlorine gas was first introduced as a weapon on April 22, 1915, at Ypres by the German Army,[36][37] and the results of this weapon were disastrous because gas masks had not yet been invented.


In industry, elemental chlorine is usually produced by the electrolysis of sodium chloride dissolved in water.[38] Along with chlorine, this chloralkali process yields hydrogen gas and sodium hydroxide, according to the following chemical equation:[10]

2 NaCl + 2 H2O → Cl2 + H2 + 2 NaOH

The electrolysis of chloride solutions all proceed according to the following equations:

Cathode: 2 H+ (aq) + 2 e → H2 (g)
Anode: 2 Cl (aq) → Cl2 (g) + 2 e

Overall process: 2 NaCl (or KCl) + 2 H2O → Cl2 + H2 + 2 NaOH (or KOH) In diaphragm cell electrolysis, an asbestos (or polymer-fiber) diaphragm separates a cathode and an anode, preventing the chlorine forming at the anode from re-mixing with the sodium hydroxide and the hydrogen formed at the cathode.[39] The salt solution (brine) is continuously fed to the anode compartment and flows through the diaphragm to the cathode compartment, where the caustic alkali is produced and the brine is partially depleted. Diaphragm methods produce dilute and slightly impure alkali but they are not burdened with the problem of preventing mercury discharge into the environment and they are more energy efficient. Membrane cell electrolysis employ permeable membrane as an ion exchanger. Saturated sodium (or potassium) chloride solution is passed through the anode compartment, leaving at a lower concentration.[40] This method is more efficient than the diaphragm cell and produces very pure sodium (or potassium) hydroxide at about 32% concentration, but requires very pure brine.

Liquid chlorine analysis

Laboratory methods

Small amounts of chlorine gas can be made in the laboratory by combining hydrochloric acid and manganese dioxide. Alternatively a strong acid such as sulfuric acid or hydrochloric acid reacts with sodium hypochlorite solution to release chlorine gas but reacts with sodium chlorate to produce chlorine gas and chlorine dioxide gas as well. In the home, accidents occur when hypochlorite bleach solutions are combined with certain acidic drain-cleaners.


Production of industrial and consumer products

Principal applications of chlorine are in the production of a wide range of industrial and consumer products.[41][42] For example, it is used in making plastics, solvents for dry cleaning and metal degreasing, textiles, agrochemicals and pharmaceuticals, insecticides, dyestuffs, household cleaning products, etc. Quantitavely, about 63% and 18% of all chlorine are used in the manufacture of organic and inorganic chlorine compounds, respectively,[38] and about 15,000 chlorine compounds are being used commercially.[23] The remaining 19% is used for bleaches and disinfection products.[38] The most significant of organic compounds in terms of production volume are 1,2-dichloroethane and vinyl chloride, intermediates in the production of PVC. Other particularly important organochlorines are methyl chloride, methylene chloride, chloroform, vinylidene chloride, trichloroethylene, perchloroethylene, allyl chloride, epichlorohydrin, chlorobenzene, dichlorobenzenes, and trichlorobenzenes. The major inorganic compounds include HCl, Cl2O, HOCl, NaClO3, chlorinated isocyanurates, AlCl3, SiCl4, SnCl4, PCl3, PCl5, POCl3, AsCl3, SbCl3, SbCl5, BiCl3, S2Cl2, SCl2, SOCI2, CIF3, ICl, ICl3, TiCl3, TiCl4, MoCl5, FeCl3, ZnCl2, etc.[38][43]

Purification and disinfection

Chlorine is an important chemical for water purification (such as water treatment plants), in disinfectants, and in bleach. Chlorine in water is more than three times as effective as a disinfectant against Escherichia coli than an equivalent concentration of bromine, and is more than six times more effective than an equivalent concentration of iodine.[44]

Chlorine is usually used (in the form of hypochlorous acid) to kill bacteria and other microbes in drinking water supplies and public swimming pools. In most private swimming pools, chlorine itself is not used, but rather sodium hypochlorite, formed from chlorine and sodium hydroxide, or solid tablets of chlorinated isocyanurates. The drawback of using chlorine in swimming pools is that the chlorine reacts with a human's hair and skin because hair and skin are made from protein.(Reaction with protein amino groups) Even small water supplies are now routinely chlorinated.[6]

It is often impractical to store and use poisonous chlorine gas for water treatment, so alternative methods of adding chlorine are used. These include hypochlorite solutions, which gradually release chlorine into the water, and compounds like sodium dichloro-s-triazinetrione (dihydrate or anhydrous), sometimes referred to as "dichlor", and trichloro-s-triazinetrione, sometimes referred to as "trichlor". These compounds are stable while solid and may be used in powdered, granular, or tablet form. When added in small amounts to pool water or industrial water systems, the chlorine atoms hydrolyze from the rest of the molecule forming hypochlorous acid (HOCl), which acts as a general biocide, killing germs, micro-organisms, algae, and so on.[45][46]

Use as a weapon

World War I

Chlorine gas, also known as bertholite, was first used as a weapon in World War I by Germany on April 22, 1915 in the Second Battle of Ypres. As described by the soldiers it had a distinctive smell of a mixture between pepper and pineapple. It also tasted metallic and stung the back of the throat and chest. Chlorine can react with water in the mucosa of the lungs to form hydrochloric acid, an irritant that can be lethal. The damage done by chlorine gas can be prevented by a gas mask, or other filtration method, which makes the overall chance of death by chlorine gas much lower than those of other chemical weapons. It was pioneered by a German scientist later to be a Nobel laureate, Fritz Haber of the Kaiser Wilhelm Institute in Berlin, in collaboration with the German chemical conglomerate IG Farben, who developed methods for discharging chlorine gas against an entrenched enemy. It is alleged that Haber's role in the use of chlorine as a deadly weapon drove his wife, Clara Immerwahr, to suicide.[47] After its first use, chlorine was utilized by both sides as a chemical weapon, but it was soon replaced by the more deadly phosgene and mustard gas.[48]

Iraq War

Chlorine "attack" on an acetal resin plumbing joint.

Chlorine gas has also been used by insurgents against the local population and coalition forces in the Iraq War in the form of chlorine bombs. On March 17, 2007, for example, three chlorine filled trucks were detonated in the Anbar province killing two and sickening over 350.[49] Other chlorine bomb attacks resulted in higher death tolls, with more than 30 deaths on two separate occasions.[50] Most of the deaths were caused by the force of the explosions rather than the effects of chlorine, since the toxic gas is readily dispersed and diluted in the atmosphere by the blast. The Iraqi authorities have tightened up security for chlorine, which is essential for providing safe drinking water for the population.

Chlorine cracking

The element is widely used for purifying water owing to its powerful oxidizing properties, especially potable water supplies and water used in swimming pools. Several catastrophic collapses of swimming pool ceilings have occurred owing to stress corrosion cracking of stainless steel rods used to suspend them.[51] Some polymers are also sensitive to attack, including acetal resin and polybutene. Both materials were used in hot and cold water domestic supplies, and stress corrosion cracking caused widespread failures in the USA in the 1980s and 1990s. One example shows an acetal joint in a water supply system, which, when it fractured, caused substantial physical damage to computers in the labs below the supply. The cracks started at injection molding defects in the joint and grew slowly until finally triggered. The fracture surface shows iron and calcium salts that were deposited in the leaking joint from the water supply before failure.[52]

Health effects

Skull and crossbones.svg
NFPA 704
NFPA 704.svg

Chlorine is a toxic gas that irritates the respiratory system. Because it is heavier than air, it tends to accumulate at the bottom of poorly ventilated spaces. Chlorine gas is a strong oxidizer, which may react with flammable materials.[53]

Chlorine is detectable with measuring devices in concentrations of as low as 0.2 parts per million (ppm), and by smell at 3 ppm. Coughing and vomiting may occur at 30 ppm and lung damage at 60 ppm. About 1000 ppm can be fatal after a few deep breaths of the gas.[23] Breathing lower concentrations can aggravate the respiratory system, and exposure to the gas can irritate the eyes.[54] The toxicity of chlorine comes from its oxidizing power. When chlorine is inhaled at concentrations above 30 ppm, it begins to react with water and cells, which change it into hydrochloric acid (HCl) and hypochlorous acid (HClO).

When used at specified levels for water disinfection, the reaction of chlorine with water is not a major concern for human health. However, other materials present in the water may generate disinfection by-products that can damage human health.[55][56]

See also


  1. ^ Chlorine, Gas Encyclopaedia, Air Liquide
  2. ^ Magnetic susceptibility of the elements and inorganic compounds, in Lide, D. R., ed (2005). CRC Handbook of Chemistry and Physics (86th ed.). Boca Raton (FL): CRC Press. ISBN 0-8493-0486-5. 
  3. ^ Kenneth Barbalace (1995-10-22). "Chemical Database: Chlorine". Retrieved 2011-09-19. 
  4. ^ "CDC | Facts About Chlorine". Retrieved 2011-09-19. 
  5. ^ Chlorine properties, NIST
  6. ^ a b Hammond, C. R. (2000). The Elements, in Handbook of Chemistry and Physics 81st edition. CRC press. ISBN 0849304814. 
  7. ^ Wiberg 2001, p. 409.
  8. ^ Greenwood 1997, pp. 857–858.
  9. ^ Greenwood 1997, p. 806.
  10. ^ a b Wiberg 2001, p. 408.
  11. ^ Greenwood 1997, pp. 844–850.
  12. ^ Greenwood 1997, p. 849.
  13. ^ Cotton, F. Albert and Wilkinson, Geoffrey (1966). Advanced Inorganic Chemistry, 2nd ed.. John Wiley & sons. p. 568. 
  14. ^ Emeléus, H. J (1961). Advances in inorganic chemistry and radiochemistry. pp. 133–143. ISBN 9780120236039. 
  15. ^ Windholz, Martha et al., ed (1976). Merck Index of Chemicals and Drugs, 9th ed.. Rahway, N.J.: Merck & Co.. ISBN 0911910263. 
  16. ^ Greenwood 1997, p. 795.
  17. ^ "Risk assessment and the cycling of natural organochlorines". Euro Chlor. Retrieved 2007-08-12. 
  18. ^ Cameron, A.G.W. (June 1957). "Stellar Evolution, Nuclear Astrophysics, and Nucleogenesis". CRL-41. 
  19. ^ a b Georges, Audi (2003). "The NUBASE Evaluation of Nuclear and Decay Properties". Nuclear Physics A (Atomic Mass Data Center) 729: 3–128. Bibcode 2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001. 
  20. ^ "The earliest salt production in the world: an early Neolithic exploitation in Poiana Slatinei-Lunca, Romania". Retrieved 2008-07-10. 
  21. ^ a b c Greenwood 1997, p. 790.
  22. ^ a b c d e f "17 Chlorine". Retrieved 2008-09-12. 
  23. ^ a b c Greenwood 1997, p. 793.
  24. ^ Greenwood 1997, p. 792.
  25. ^ Ihde, Aaron John (1984). The development of modern chemistry. Courier Dover Publications. p. 158. ISBN 0486642356. 
  26. ^ Weeks, Mary Elvira (1932). "The discovery of the elements. XVII. The halogen family". Journal of Chemical Education 9 (11): 1915. Bibcode 1932JChEd...9.1915W. doi:10.1021/ed009p1915. 
  27. ^ Gay-Lussac, Joseph Louis; Thénard, Louis-Jacques (1809). "On the nature and the properties of muriatic acid and of oxygenated muriatic acid". Mémoires de Physique et de Chimie de la Société d'Arcueil 2: 339–358. 
  28. ^ Sir Humphry Davy (1811). "On a Combination of Oxymuriatic Gas and Oxygene Gas". Philosophical Transactions of the Royal Society 101: 155–162. doi:10.1098/rstl.1811.0008. 
  29. ^ Greenwood 1997, p. 789.
  30. ^ Snelders, H. A. M. (1971). "J. S. C. Schweigger: His Romanticism and His Crystal Electrical Theory of Matter". Isis 62 (3): 328. doi:10.1086/350763. JSTOR 229946. 
  31. ^ "This Month in Physics History September 4, 1821 and August 29, 1831: Faraday and Electromagnetism". Retrieved 2010-05-08. 
  32. ^ "Michael Faraday". Retrieved 2010-05-08. 
  33. ^ "History of Chlorine". Retrieved 2008-07-10. 
  34. ^ a b c d Jacqueline Brazin. "Chlorine & its Consequences". Archived from the original on September 18, 2006. Retrieved 2008-07-10. 
  35. ^ "Chlorine Story". americanchemistry. Retrieved 2008-07-10. 
  36. ^ "Chlorine – History". Retrieved 2008-07-10. 
  37. ^ "Weaponry: Use of Chlorine Gas Cylinders in World War I". Retrieved 2008-07-10. 
  38. ^ a b c d Greenwood 1997, p. 798.
  39. ^ "Diaphragm cell". Euro Chlor. Retrieved 2007-08-15. 
  40. ^ "Membrane cell". Euro Chlor. Retrieved 2007-08-15. 
  41. ^ "Uses". Euro Chlor. Retrieved 2007-08-20. 
  42. ^ "Chlorine Tree". Chlorine Tree. Retrieved 2007-08-20. 
  43. ^ Wiberg 2001, p. 412.
  44. ^ Koski TA, Stuart LS, Ortenzio LF (1966). "Comparison of chlorine, bromine, iodine as disinfectants for swimming pool water". Applied Microbiology 14 (2): 276–279. PMC 546668. PMID 4959984. 
  45. ^ Greenwood 1997, p. 860.
  46. ^ Wiberg 2001, p. 411.
  47. ^ Smil, Vaclav (2004-04-01). Enriching the Earth: Fritz Haber, Carl Bosch, and the Transformation of World Food Production. p. 226. ISBN 9780262693134. 
  48. ^ "Weapons of War: Poison Gas". First World Retrieved 2007-08-12. 
  49. ^ Mahdi, Basim (2007-03-17). "Iraq gas attack makes hundreds ill". CNN. Retrieved 2007-03-17. 
  50. ^ "'Chlorine bomb' hits Iraq village". BBC News. 2007-05-17. Retrieved 2007-05-17. 
  51. ^ Bertolini, Luca; Elsener, Bernhard; Pedeferri, Pietro; Polder, Rob B. (2004). Corrosion of steel in concrete: prevention, diagnosis, repair. Wiley-VCH. p. 148. ISBN 3527308008. 
  52. ^ Lewis, P.R. (1 January 2000). Polymer Product Failure. iSmithers Rapra Publishing. pp. 19–. ISBN 9781859571927. Retrieved 30 April 2011. 
  53. ^ "Chlorine MSDS". October 23, 1997 (Revised November 1999. 
  54. ^ Winder, Chris (2001). "The Toxicology of Chlorine". Environmental Research 85 (2): 105–114. Bibcode 2001ER.....85..105W. doi:10.1006/enrs.2000.4110. PMID 11161660. 
  55. ^ "What's in your Water?: Disinfectants Create Toxic By-products". ACES News. College of Agricultural, Consumer and Environmental Sciences – University of Illinois at Urbana-Champaign. 2009-03-31. Retrieved 2009-03-31. 
  56. ^ Richardson, Susan D.; Plewa, Michael J.; Wagner, Elizabeth D.; Schoeny, Rita; DeMarini, David M. (2007). "Occurrence, genotoxicity, and carcinogenicity of regulated and emerging disinfection by-products in drinking water: A review and roadmap for research". Mutation Research/Reviews in Mutation Research 636: 178–242. doi:10.1016/j.mrrev.2007.09.001. 


  • Greenwood, Norman N; Earnshaw, Alan (1997). Chemistry of the Elements (2 ed.). Oxford: Butterworth-Heinemann. ISBN 0080379419. 
  • Wiberg, Egon; Wiberg, Nils and Holleman, Arnold Frederick (2001). Inorganic Chemistry. Academic Press. ISBN 0123526515. 

External links

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Chlorine — Chlo rine, n. [Gr. ? pale green, greenish yellow. So named from its color. See {Yellow}.] (Chem.) One of the elementary substances, commonly isolated as a greenish yellow gas, two and one half times as heavy as air, of an intensely disagreeable… …   The Collaborative International Dictionary of English

  • Chlorine — (Chem.), so v. w. Chlor …   Pierer's Universal-Lexikon

  • Chlorīne — Chlorīne, veralteter Name des Chlors; s. auch Resorcin …   Meyers Großes Konversations-Lexikon

  • chlorine — Symbol: Cl Atomic number: 17 Atomic weight: 35.453 Halogen element. Poisonous greenish yellow gas. Occurs widely in nature as sodium chloride in seawater. Reacts directly with many elements and compounds, strong oxidizing agent. Discovered by… …   Elements of periodic system

  • chlorine — nonmetallic element, coined 1810 by English chemist Sir Humphry Davy (1778 1829) from Gk. khloros pale green (see CHLOE (Cf. Chloe)) + chemical suffix INE (Cf. ine) (2). Named for its color. Discovered 1774, but known at first as oxymuriatic acid …   Etymology dictionary

  • chlorine — ► NOUN ▪ a poisonous, irritant, pale green gaseous chemical element. ORIGIN from Greek khl ros green …   English terms dictionary

  • chlorine — [klôr′ēn΄, klôr′in] n. [< Gr chlōros, pale green (< IE * ghlō , var. of base * ghel : see YELLOW) + INE3: so named (1810) by DAVY Sir Humphry, who proved it to be an element, for its color] a greenish yellow, poisonous, gaseous chemical… …   English World dictionary

  • chlorine — chlorinous, adj. /klawr een, in, klohr /, n. a halogen element, a heavy, greenish yellow, incombustible, water soluble, poisonous gas that is highly irritating to the respiratory organs, obtained chiefly by electrolysis of sodium chloride brine:… …   Universalium

  • Chlorine — En chimie organique un chlorine est un grand anneau aromatique hétérocyclique consistant, au noyau, de 3 pyrroles et d un pyrrole réduit couplé à travers 4 liens méthine. À l inverse d un porphyrine, un chlorine est donc largement aromatique mais …   Wikipédia en Français

  • chlorine — [19] Chlorine is a greenish yellow gas, and was named for its colour. The term was coined by the British chemist Sir Humphry Davy in 1810, from the Greek khlōrós ‘greenishyellow’. Of other words containing this element, chlorophyll [19] too was… …   The Hutchinson dictionary of word origins

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”