Chlorine

17 sulfur ← chlorine → argon F ↑ Cl ↓ Br periodic table
General
Name, Symbol, Number	chlorine, Cl, 17
Chemical series	halogens
Group, Period, Block	17, 3, p
Appearance	yellowish green
Atomic mass	35.453(2) g/mol
Electron configuration	[Ne] 3s2 3p5
Electrons per shell	2, 8, 7
Physical properties
Phase	gas
Density	(0 °C, 101.325 kPa) 3.2 g/L
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
Heat of vaporization	(Cl2) 20.41 kJ/mol
Heat capacity	(25 °C) (Cl2) 33.949 J/(mol·K)
Vapor pressure P/Pa 1 10 100 1 k 10 k 100 k at T/K 128 139 153 170 197 239
Atomic properties
Crystal structure	orthorhombic
Oxidation states	±1, 3, 5, 7 (strongly acidic oxide)
Electronegativity	3.16 (Pauling scale)
Ionization energies (more)	1st: 1251.2 kJ/mol
	2nd: 2298 kJ/mol
	3rd: 3822 kJ/mol
Atomic radius	100 pm
Atomic radius (calc.)	79 pm
Covalent radius	99 pm
Van der Waals radius	175 pm
Miscellaneous
Magnetic ordering	nonmagnetic
Electrical resistivity	(20 °C) > 10 Ω·m
Thermal conductivity	(300 K) 8.9 mW/(m·K)
Speed of sound	(gas, 0 °C) 206 m/s
CAS registry number	7782-50-5
Notable isotopes
Main article: Isotopes of chlorine iso NA half-life DM DE (MeV) DP 35Cl 75.77% Cl is stable with 18 neutrons 36Cl syn 3.01×105 y β- 0.709 36Ar ε - 36S 37Cl 24.23% Cl is stable with 20 neutrons

Chlorine (chemical symbol Cl, atomic number 17)

It is a halogen, found in the periodic table in group 17. As the chloride ion, which is part of common salt and other compounds, it is abundant in nature and necessary to most forms of life, including humans. In its elemental form under standard conditions, it is a pale green gas about 2.5 times as dense as air. It has a disagreeable suffocating odor and is poisonous. Chlorine is a powerful oxidant and is used in bleaching and disinfectants.

Discovery

Chlorine was discovered in 1774 by Swedish chemist Carl Wilhelm Scheele, who observed the greenish-yellow gas when experimenting with seawater. He mistakenly thought it was a compound of oxygen and hydrochloric acid (HCl), and he called it dephlogisticated marine acid. He used the term "dephlogisticated" to indicate that the material could not burn, and the term "marine acid" was the name for hydrochloric acid. (According to the "phlogiston theory" commonly held at that time, phlogiston was an invisible, weightless substance released by burning materials. When a material could no longer burn, it was said to be "dephlogisticated.")

In 1810, Sir Humphry Davy's experiments indicated that this gas was an element, not a compound. He named it chlorine, from the Greek word χλωρóς (chloros), meaning greenish yellow.

Occurrence

In nature, chlorine is found mainly 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. Common chloride minerals include halite (sodium chloride), sylvite (potassium chloride), and carnallite (potassium magnesium chloride hexahydrate).

Industrially, elemental chlorine is usually produced by the electrolysis of sodium chloride dissolved in water. Along with chlorine, this chloralkali process yields hydrogen gas and sodium hydroxide, according to the chemical equation

2 NaCl + 2 H₂O → Cl₂ + H₂ + 2 NaOH

Notable characteristics

Chlorine is diatomic with the formula Cl₂. It combines readily with nearly all other elements, although is not so extremely reactive as fluorine. At 10 °C one liter of water dissolves 3.10 litres of gaseous chlorine and at 30 °C only 1.77 litres.

This element is a member of the salt-forming halogen series and is extracted from chlorides through oxidation often by electrolysis.

As the chloride ion, Cl^–, it is also the most abundant dissolved species in ocean water.

Isotopes

Chlorine has 9 isotopes with mass numbers ranging from 32 to 40. There are two principal stable isotopes, ³⁵Cl (75.77%)and ³⁷Cl (24.23%), found in the relative proportions of 3:1 respectively, giving chlorine atoms in bulk an apparent atomic weight of 35.5.

³⁶Cl

Trace amounts of radioactive ³⁶Cl exist in the environment, about 700*10^-15 to 1. 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.

Chlorine gas extraction

Chlorine can be manufactured by electrolysis of a sodium chloride solution (brine). There are three industrial methods for the extraction of chlorine by electrolysis.

Mercury cell electrolysis

Mercury cell electrolysis was the first method used to produce chlorine on an industrial scale. Titanium anodes are located above a liquid mercury cathode and a solution of sodium chloride is positioned between the electrodes. When an electrical current is applied, chloride is released at the titanium anodes and sodium dissolves into the mercury cathode forming an amalgam.

The amalgam can be regenerated into mercury by reacting it with water, producing hydrogen and sodium hydroxide. These are useful byproducts.

This method consumes vast amounts of energy and there are also concerns about mercury emissions.

Diaphragm cell electrolysis

An asbestos diaphragm is deposited on an iron grid cathode preventing the chlorine forming at the anode and the sodium hydroxide forming at the cathode from re-mixing.

This method uses less energy than the mercury cell, but the sodium hydroxide is not as easily concentrated and precipitated into a useful substance.

Membrane cell electrolysis

The electrolysis cell is divided into two by a membrane acting as an ion exchanger. Saturated sodium chloride solution is passed through the anode compartment leaving a lower concentration. Sodium hydroxide solution is circulated through the cathode compartment exiting at a higher concentration. A portion of this concentrated sodium hydroxide solution is diverted as product while the remainder is diluted with deionized water and passed through the electrolyzer again.

This method is nearly as efficient as the diaphragm cell and produces very pure sodium hydroxide but requires very pure sodium chloride solution..

Cathode: 2 H⁺(aq) + 2e^– ---> H₂(g)

Anode: 2Cl^– ---> Cl₂ (g) + 2e^–

Overall equation: 2NaCl + 2H₂0 ---> Cl₂ + H₂ + 2 NaOH

Other methods

Before electrolytic methods were used for chlorine production, the direct oxidation of hydrogen chloride with oxygen or air was exercised in the Deacon process:

4HCl + O₂ → 2Cl₂ + 2H₂O

This reaction was accomplished with the use of CuCl₂ as a catalyst. Due to the extremely corrosive reaction mixture, industrial use of this method is difficult.

Another earlier process to produce chlorine is to heat brine with acid and manganese dioxide.

2NaCl + 2H₂SO₄ + MnO₂ → Na₂SO₄ + MnSO₄ + 2H₂O + Cl₂

Using this process, chemist Carl Wilhelm Scheele was the first to isolate chlorine in a laboratory. The manganese can be recovered by the Weldon process.

In a laboratory, small amounts of chlorine gas can be created by adding concentrated hydrochloric acid (typically about 5M) to sodium chlorate solution.

Applications and Uses

Purification and Disinfection

Chlorine is an important chemical for some processes of water purification, in disinfectants, and in bleach. Ozone can also be used for killing bacteria, and is preferred by many municipal drinking water systems because ozone does not form organochlorine compounds and does not remain in the water after treatment.

Chlorine is also used widely in the manufacture of many every-day items, or to purify water in various forms.

• Used (in the form of hypochlorous acid) to kill bacteria and other microbes from drinking water supplies and swimming pools. Even small water supplies are now routinely chlorinated. (See Also: chlorination)
• Used widely in paper product production, antiseptic, dyestuffs, food, insecticides, paints, petroleum products, plastics, medicines, textiles, solvents, and many other consumer products.

Oxidizing agent

Chlorine is used extensively in organic and inorganic chemistry as an oxidizing agent and in substitution reactions because chlorine often imparts many desired properties in an organic compound when it is substituted for hydrogen (as in synthetic rubber production).It has the highest electron affinity among halides.

World War I

• Chlorine gas, also known as bertholite, was first used as a chemical weapon against humans during World War I. German chemical conglomerate IG Farben had been producing chlorine as a by-product of their dye manufacturing process. In cooperation with Fritz Haber of the Kaiser Wilhelm Institute for Chemistry in Berlin, they developed methods of discharging chlorine gas against entrenched enemy.

Compounds

For general references to the chloride ion (Cl⁻), including references to specific chlorides, see chloride. For other chlorine compounds see chlorate (ClO₃⁻), chlorite (ClO₂⁻), hypochlorite(ClO⁻), and perchlorate (ClO₄⁻).

See also chloramine (NH₂Cl),

• Fluorides: chlorine monofluoride (ClF), chlorine trifluoride (ClF₃), chlorine pentafluoride (ClF₅)
• Oxides: chlorine dioxide (ClO₂), dichlorine monoxide (Cl₂O), dichlorine heptoxide (Cl₂O₇)
• Acids: hydrochloric acid (HCl), chloric acid (HClO₃), and perchloric acid (HClO₄)

See also Chlorine compounds.

Other Uses

It is also used in the production of chlorates, chloroform, carbon tetrachloride, and in bromine extraction.

Safety

Chlorine is a toxic gas that irritates the respiratory systems. Because it is heavier than air it tends to accumulate at the bottom of poorly ventilated spaces. Chlorine gas is a potential oxidizer, which may react with flammable materials. For more information see an MSDS

References

ISBN links support NWE through referral fees

• Los Alamos National Laboratory – Chlorine

See also

• Chloride

External links

• Chlorine Institute (trade organization, located in Arlington Va. USA, consisting of chlorine producers, packagers, responders, end users and associated members)
• Computational Chemistry Wiki
• National Pollutant Inventory - Chlorine
• WebElements.com – Chlorine
• Chlorine Tree

Template:ChemicalSources

Agents of Chemical Warfare
Blood agents:	Cyanogen chloride (CK) – Hydrogen cyanide (AC)
Blister agents:	Lewisite (L) – Sulfur mustard gas (HD, H, HT, HL, HQ) – Nitrogen mustard gas (HN1, HN2, HN3)
Nerve agents:	G-Agents: Tabun (GA) – Sarin (GB) – Soman (GD) – Cyclosarin (GF) | V-Agents: VE – VG – VM – VX
Pulmonary agents:	Chlorine – Chloropicrin (PS) – Phosgene (CG) – Diphosgene (DP)
Incapacitating agents:	Agent 15 (BZ) – KOLOKOL-1
Riot control agents:	Pepper spray (OC) – CS gas – CN gas (mace) – CR gas

E numbers
Colours (E100-199) • Preservatives (E200-299) • Antioxidants & Acidity regulators (E300-399) • Thickeners, stabilisers & emulsifiers (E400-499) • pH regulators & anti-caking agents (E500-599) • Flavour enhancers (E600-699) • Miscellaneous (E900-999) • Additional chemicals (E1100-1599)
Waxes (E900-909) • Synthetic glazes (E910-919) • Improving agents (E920-929) • Packaging gases (E930-949) • Sweeteners (E950-969) • Foaming agents (E990-999)
L-cysteine (E920) • L-cystine (E921) • Potassium persulfate (E922) • Ammonium persulfate (E923) • Potassium bromate (E924) • Chlorine (E925) • Chlorine dioxide (E926) • Azodicarbonamide (E927) • Carbamide (E927b) • Benzoyl peroxide (E928) • Calcium peroxide (E930)

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