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) is a nonmetal that belongs to a group of chemical elements known as halogens. At ordinary temperatures and pressures, pure chlorine is a highly reactive, poisonous gas, with a greenish-yellow color and a suffocating, disagreeable odor. Its chemical formula is Cl₂, and it is about 2.5 times as dense as air. Given its high reactivity, the free element is not found in nature.

On the other hand, chloride (Cl⁻) ions are abundant in nature and necessary for most forms of life, including human life. They are part of various salts and are dissolved in naturally occurring waters. Common salt or table salt is the compound sodium chloride (NaCl).

• Chlorine is a powerful oxidant and is used in bleaching and disinfectants.

Occurrence

As noted above, elemental chlorine is not found in nature. Rather, chlorine is found mainly in the form of the chloride ion, a component of salts deposited in the earth or dissolved in the oceans. About 1.9% of the mass of seawater is chloride ions. Higher concentrations of chloride are found in the Dead Sea and in underground brine deposits.

Given that most chloride salts are soluble in water, the abundance of chloride-containing minerals is higher in regions with dry climates and deep underground, where the salts seldom come in contact with water. Common chloride minerals include halite (sodium chloride), sylvite (potassium chloride), and carnallite (potassium magnesium chloride hexahydrate).

Discovery and production

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.

Industrially, elemental chlorine is usually produced by the electrolysis of sodium chloride (NaCl) dissolved in water. Along with chlorine, this process yields hydrogen (H₂) gas and sodium hydroxide (NaOH), according to the chemical equation

2 NaCl + 2 H₂O → Cl₂ + H₂ + 2 NaOH

Notable characteristics

In the periodic table, chlorine is located in group 17 (former group 7A), the halogen family, between fluorine and bromine. In addition, it lies in period 3, between sulfur and argon.

Elemental chlorine (Cl₂) is a strong oxidizing agent and combines readily with nearly all other elements. It is not, however, as extremely reactive as fluorine. It reacts with some metals (in the presence of water) to form chloride salts. In addition, it combines with metals and oxygen to form chlorate (ClO₃⁻) salts. Chlorine also forms compounds with various nonmetals.

One liter of water dissolves 3.10 liters of gaseous chlorine at 10 °C, but the same amount of water dissolves only 1.77 liters chlorine gas at 30 °C. In water, it exists as a mixture of chlorine (Cl₂), hydrochloric acid (HCl), and hypochlorous acid (HOCl).

Isotopes

Chlorine has nine isotopes, with atomic mass numbers ranging from 32 to 40. Of these, the two main, stable isotopes are ³⁵Cl (75.77%) and ³⁷Cl (24.23%). As the relative proportions of these two isotopes are 3:1 respectively, chlorine atoms in bulk have an apparent atomic weight of 35.5 atomic mass units.

The environment also contains trace amounts of the radioactive isotope ³⁶Cl. It decays to sulfur-36 and argon-36, with a combined half-life of 308,000 years. Based on its half-life, high solubility in water, and nonreactive nature, this isotope is suitable for geologic dating in the range of 60,000 to 1 million years.

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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