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Chlorine

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


                17                sulfur ← chlorine → argon
                 F
                ↑
                Cl
                ↓
                Br

                                  Periodic Table - Extended 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] 3s^2 3p^5
                                               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 (Cl[2]) 6.406 kJ·mol^−1
                           Heat of vaporization (Cl[2]) 20.41 kJ·mol^−1
                                            Heat capacity (25 °C) (Cl[2])
                                                33.949 J·mol^−1·K^−1

   CAPTION: 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^−1
                                                    2nd: 2298 kJ·mol^−1
                                                    3rd: 3822 kJ·mol^−1
                                                      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^−1·K^−1
                                       Speed of sound (gas, 0 °C) 206 m/s
                                             CAS registry number 7782-50-5
                                                         Selected isotopes

                 CAPTION: Main article: Isotopes of chlorine

                                iso    NA   half-life  DM  DE ( MeV)  DP
                               ^35Cl 75.77% Cl is stable with 18 neutrons
                               ^36Cl syn    301×10^3 y β^- 0.709     ^36Ar
                                                       ε   -         ^36S
                               ^37Cl 24.23% Cl is stable with 20 neutrons

                                                                References

   Chlorine ( IPA: /ˈklɔːriːn/, Greek: χλωρóς chloros, meaning "pale
   green"), is the chemical element with atomic number 17 and symbol Cl.
   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 odour and is poisonous. Chlorine is a powerful oxidant and
   is used in bleaching and disinfectants.

Notable characteristics

   Chlorine gas is diatomic with the formula Cl[2]. It combines readily
   with nearly all other elements, although it is not as extremely
   reactive as fluorine. At 10 ° C one litre 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.

History

   Chlorine was discovered in 1774 by Swedish chemist Carl Wilhelm
   Scheele, who called it dephlogisticated marine acid (see Phlogiston
   theory) and mistakenly thought it contained oxygen. Chlorine was given
   its current name in 1810 by Sir Humphry Davy, who insisted that it was
   in fact an element.

   Chlorine gas, also known as bertholite, was first used as a weapon
   against humans in World War I by Germany on April 22nd, 1915. It was
   pioneered by a German scientist later to be a Nobel laureate, Fritz
   Haber. It is alleged that his role in the use of chlorine as a deadly
   weapon drove his wife to suicide. After its first use, it was utilised
   by both sides as a chemical weapon.

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 H[2]O → Cl[2] + H[2] + 2 NaOH

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, in a ratio
   of about 700x10^-15 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.

Chlorine gas extraction

   Chlorine can be manufactured by electrolysis of a sodium chloride
   solution ( brine). The production of chlorine results in the
   co-products caustic soda (sodium hydroxide, NaOH) and hydrogen gas
   (H[2]). These two products, as well as chlorine are highly reactive.
   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.
   However, this method consumes vast amounts of energy and there are also
   concerns about mercury emissions.

Diaphragm cell electrolysis

   In 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) + 2 e^– → H[2 (g)]
          Anode: 2 Cl^– → Cl[2 (g)] + 2 e^–

   Overall equation: 2 NaCl + 2H[2]0 → Cl[2] + H[2] + 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:

          4 HCl + O[2] → 2 Cl[2] + 2 H[2]O

   This reaction was accomplished with the use of CuCl[2] as a catalyst.
   Due to the extremely corrosive reaction mixture, industrial use of this
   method is difficult.

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

          2 NaCl + 2H[2]SO[4] + MnO[2] → Na[2]SO[4] + MnSO[4] + 2 H[2]O +
          Cl[2]

   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. However,
       in most non-commercial swimming pools chlorine itself is not used,
       but rather the mixture sodium hypochloride, a mixture of sodium and
       chlorine. 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 to an organic compound when it is
   substituted for hydrogen (as in synthetic rubber production) because of
   its high electron affinity.

World War I

   Chlorine became the first killing agent to be employed during World War
   I. German chemical conglomerate IG Farben had been producing chlorine
   as a by-product of their dye manufacturing. In cooperation with Fritz
   Haber of the Kaiser Wilhelm Institute for Chemistry in Berlin, they
   developed methods of discharging chlorine gas against an en trenched
   enemy.

Compounds

   For general references to the chloride ion (Cl^−), including references
   to specific chlorides, see chloride. For other chlorine compounds see
   chlorate (ClO[3]^−), chlorite (ClO[2]^−), hypochlorite(ClO^−), and
   perchlorate(ClO[4]^−), and chloramine (NH[2]Cl).

   See also:
     * Fluorides: chlorine monofluoride (ClF), chlorine trifluoride
       (ClF[3]), chlorine pentafluoride (ClF[5])
     * Oxides: chlorine dioxide (ClO[2]), dichlorine monoxide (Cl[2]O),
       dichlorine heptoxide (Cl[2]O[7])
     * Acids: hydrochloric acid (HCl), chloric acid (HClO[3]), and
       perchloric acid (HClO[4])

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 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. For more information see an MSDS.

   Retrieved from " http://en.wikipedia.org/wiki/Chlorine"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
