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Chlorine | ||||||||||||||||||||||||||||
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Pronunciation | /ˈklɔːriːn, -aɪn/ | |||||||||||||||||||||||||||
Appearance | pale yellow-green gas | |||||||||||||||||||||||||||
Standard atomic weight Ar°(Cl) | ||||||||||||||||||||||||||||
Chlorine in the periodic table | ||||||||||||||||||||||||||||
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Atomic number (Z) | 17 | |||||||||||||||||||||||||||
Group | group 17 (halogens) | |||||||||||||||||||||||||||
Period | period 3 | |||||||||||||||||||||||||||
Block | p-block | |||||||||||||||||||||||||||
Electron configuration | [Ne] 3s2 3p5 | |||||||||||||||||||||||||||
Electrons per shell | 2, 8, 7 | |||||||||||||||||||||||||||
Physical properties | ||||||||||||||||||||||||||||
Phase at STP | gas | |||||||||||||||||||||||||||
Melting point | (Cl2) 171.6 K (−101.5 °C, −150.7 °F) | |||||||||||||||||||||||||||
Boiling point | (Cl2) 239.11 K (−34.04 °C, −29.27 °F) | |||||||||||||||||||||||||||
Density (at STP) | 3.2 g/L | |||||||||||||||||||||||||||
when liquid (at b.p.) | 1.5625 g/cm3[3] | |||||||||||||||||||||||||||
Triple point | 172.22 K, 1.392 kPa[4] | |||||||||||||||||||||||||||
Critical point | 416.9 K, 7.991 MPa | |||||||||||||||||||||||||||
Heat of fusion | (Cl2) 6.406 kJ/mol | |||||||||||||||||||||||||||
Heat of vaporisation | (Cl2) 20.41 kJ/mol | |||||||||||||||||||||||||||
Molar heat capacity | (Cl2) 33.949 J/(mol·K) | |||||||||||||||||||||||||||
Vapour pressure
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Atomic properties | ||||||||||||||||||||||||||||
Oxidation states | −1, 0, +1, +2, +3, +4, +5, +6, +7 (a strongly acidic oxide) | |||||||||||||||||||||||||||
Electronegativity | Pauling scale: 3.16 | |||||||||||||||||||||||||||
Ionisation energies |
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Covalent radius | 102±4 pm | |||||||||||||||||||||||||||
Van der Waals radius | 175 pm | |||||||||||||||||||||||||||
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Other properties | ||||||||||||||||||||||||||||
Natural occurrence | primordial | |||||||||||||||||||||||||||
Crystal structure | orthorhombic (oS8) | |||||||||||||||||||||||||||
Lattice constants | a = 630.80 pm b = 455.83 pm c = 815.49 pm (at triple point)[5] | |||||||||||||||||||||||||||
Thermal conductivity | 8.9×10−3 W/(m⋅K) | |||||||||||||||||||||||||||
Electrical resistivity | >10 Ω⋅m (at 20 °C) | |||||||||||||||||||||||||||
Magnetic ordering | diamagnetic[6] | |||||||||||||||||||||||||||
Molar magnetic susceptibility | −40.5×10−6 cm3/mol[7] | |||||||||||||||||||||||||||
Speed of sound | 206 m/s (gas, at 0 °C) | |||||||||||||||||||||||||||
CAS Number | Cl2: 7782-50-5 | |||||||||||||||||||||||||||
History | ||||||||||||||||||||||||||||
Discovery and first isolation | Carl Wilhelm Scheele (1774) | |||||||||||||||||||||||||||
Recognized as an element by | Humphry Davy (1808) | |||||||||||||||||||||||||||
Isotopes of chlorine | ||||||||||||||||||||||||||||
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Chlorine is a chemical element; it has symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine is a yellow-green gas at room temperature. It is an extremely reactive element and a strong oxidising agent: among the elements, it has the highest electron affinity and the third-highest electronegativity on the revised Pauling scale, behind only oxygen and fluorine.
Chlorine played an important role in the experiments conducted by medieval alchemists, which commonly involved the heating of chloride salts like ammonium chloride (sal ammoniac) and sodium chloride (common salt), producing various chemical substances containing chlorine such as hydrogen chloride, mercury(II) chloride (corrosive sublimate), and aqua regia. However, the nature of free chlorine gas as a separate substance was only recognised around 1630 by Jan Baptist van Helmont. Carl Wilhelm Scheele wrote a description of chlorine gas in 1774, supposing it to be an oxide of a new element. In 1809, chemists suggested that the gas might be a pure element, and this was confirmed by Sir Humphry Davy in 1810, who named it after the Ancient Greek χλωρός (khlōrós, "pale green") because of its colour.
Because of its great reactivity, all chlorine in the Earth's crust is in the form of ionic chloride compounds, which includes table salt. It is the second-most abundant halogen (after fluorine) and twenty-first most abundant chemical element in Earth's crust. These crustal deposits are nevertheless dwarfed by the huge reserves of chloride in seawater.
Elemental chlorine is commercially produced from brine by electrolysis, predominantly in the chloralkali process. The high oxidising potential of elemental chlorine led to the development of commercial bleaches and disinfectants, and a reagent for many processes in the chemical industry. Chlorine is used in the manufacture of a wide range of consumer products, about two-thirds of them organic chemicals such as polyvinyl chloride (PVC), many intermediates for the production of plastics, and other end products which do not contain the element. As a common disinfectant, elemental chlorine and chlorine-generating compounds are used more directly in swimming pools to keep them sanitary. Elemental chlorine at high concentration is extremely dangerous, and poisonous to most living organisms. As a chemical warfare agent, chlorine was first used in World War I as a poison gas weapon.
In the form of chloride ions, chlorine is necessary to all known species of life. Other types of chlorine compounds are rare in living organisms, and artificially produced chlorinated organics range from inert to toxic. In the upper atmosphere, chlorine-containing organic molecules such as chlorofluorocarbons have been implicated in ozone depletion. Small quantities of elemental chlorine are generated by oxidation of chloride ions in neutrophils as part of an immune system response against bacteria.
History
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.[9]
Early discoveries
Around 900, the authors of the Arabic writings attributed to Jabir ibn Hayyan (Latin: Geber) and the Persian physician and alchemist Abu Bakr al-Razi (c. 865–925, Latin: Rhazes) were experimenting with sal ammoniac (ammonium chloride), which when it was distilled together with vitriol (hydrated sulfates of various metals) produced hydrogen chloride.[10] However, it appears that in these early experiments with chloride salts, the gaseous products were discarded, and hydrogen chloride may have been produced many times before it was discovered that it can be put to chemical use.[11] One of the first such uses was the synthesis of mercury(II) chloride (corrosive sublimate), whose production from the heating of mercury either with alum and ammonium chloride or with vitriol and sodium chloride was first described in the De aluminibus et salibus ("On Alums and Salts", an eleventh- or twelfth century Arabic text falsely attributed to Abu Bakr al-Razi and translated into Latin in the second half of the twelfth century by Gerard of Cremona, 1144–1187).[12] Another important development was the discovery by pseudo-Geber (in the De inventione veritatis, "On the Discovery of Truth", after c. 1300) that by adding ammonium chloride to nitric acid, a strong solvent capable of dissolving gold (i.e., aqua regia) could be produced.[13] Although aqua regia is an unstable mixture that continually gives off fumes containing free chlorine gas, this chlorine gas appears to have been ignored until c. 1630, when its nature as a separate gaseous substance was recognised by the Brabantian chemist and physician Jan Baptist van Helmont.[14][en 1]
![](http://upload.wikimedia.org/wikipedia/commons/thumb/4/4d/PSM_V31_D740_Carl_Wilhelm_Scheele.jpg/140px-PSM_V31_D740_Carl_Wilhelm_Scheele.jpg)
Isolation
The element was first studied in detail in 1774 by Swedish chemist Carl Wilhelm Scheele, and he is credited with the discovery.[15][16] Scheele produced chlorine by reacting MnO2 (as the mineral pyrolusite) with HCl:[14]
- 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 colour, and the smell similar to aqua regia.[17] 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").[16] He failed to establish chlorine as an element.[16]
Common chemical theory at that time held that an acid is a compound that contains oxygen (remnants of this survive in the German and Dutch names of oxygen: sauerstoff or zuurstof, both translating into English as acid substance), 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.[18][19]
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).[16] 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.[20]
Zdroj:https://en.wikipedia.org?pojem=Chlorine
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