Chlorine

Properties and Abundance of Chlorine
– Chlorine is a chemical element with symbol Cl and atomic number 17.
– It is a yellow-green gas at room temperature.
– Chlorine is highly reactive and a strong oxidizing agent.
– It has the highest electron affinity among the elements.
– Chlorine is the third-highest electronegative element on the Pauling scale.
– Chlorine is the second-most abundant halogen in the Earth’s crust.
– It is primarily found in ionic chloride compounds, including table salt.
– Elemental chlorine is commercially produced from brine by electrolysis.

Role in History and Early Discoveries
– Chlorine played a significant role in the experiments of medieval alchemists.
– It was first recognized as a separate substance in the 17th century.
– Carl Wilhelm Scheele described chlorine gas in 1774.
– In 1809, chemists suggested that chlorine might be a pure element.
– Sir Humphry Davy confirmed chlorine as an element in 1810.
– Evidence of chloride salts being used dates back to ancient times.
– Early experiments with chloride salts produced hydrogen chloride.

Importance in Life and Uses
– Chlorine in the form of chloride ions is essential for all known species of life.
– Chlorine compounds are rare in living organisms, but some are artificially produced and can be toxic.
– Chlorine-containing organic molecules, such as chlorofluorocarbons, have been implicated in ozone depletion.
– Small quantities of elemental chlorine are generated by the immune system in response to bacteria.
– Chlorine is used in swimming pools to maintain sanitation.
– Chlorine gas was first used by French chemist Claude Berthollet in 1785 to bleach textiles.
– Sodium hypochlorite, a modern bleach, was first produced by Berthollet in 1789.
– Calcium hypochlorite, a more efficient bleach, was developed by Charles Tennant in the 19th century.
– The chloralkali process was introduced in 1892 for the production of chlorine and sodium hydroxide.
– Chlorine has been used as an anti-putrefaction agent and disinfectant since the 1820s.

Chlorine as a Weapon and Chemical Reactions
– Chlorine gas was first used as a weapon by the German Army in 1915.
– Its use at the Second Battle of Ypres had a devastating effect on the allies.
– Existing gas masks were difficult to deploy and not widely distributed.
– Chlorine gas attacks the respiratory system and can cause severe injuries and death.
– Chlorine is a strong oxidizing agent and reacts with many elements to complete its outer shell.
– It is a weaker oxidizing agent than fluorine but stronger than bromine.
– The chloride ion is a weaker reducing agent than bromide but stronger than fluoride.
– Chlorine reacts with compounds containing M-M, M-H, or M-C bonds to form M-Cl bonds.
– Chlorination often leads to higher oxidation states than bromination or iodination but lower than fluorination.

Chlorine Compounds and Reactions
– Hydrogen chloride (HCl) is a major chemical in industry and laboratories.
– It can be produced by burning hydrogen gas in chlorine gas or by treating sodium chloride with concentrated sulfuric acid.
– Hydrochloric acid (HCl) is a strong acid and has many hydrates.
– Chlorine forms three fluorides: ClF, ClF2, and ClF3.
– Chlorine trifluoride (ClF3) is a highly reactive compound that can ignite many substances, including water and noble metals.
– Chlorine pentafluoride (ClF5) is a strong fluorinating agent and reacts with water to form chloryl fluoride.
– Chlorine oxides are unstable compounds that are produced during the photolysis of chlorofluorocarbons.
– Chlorine dioxide (ClO2) is a yellow gas and is used as a disinfectant.
– Chlorides can be made by reacting an element or its oxide, hydroxide, or carbonate with hydrochloric acid.
– Metal chlorides with low oxidation states are usually ionic, while nonmetals tend to form covalent molecular chlorides. Source:  https://en.wikipedia.org/wiki/Chlorine

Chlorine (Wikipedia)

Not to be confused with chloride.

This article is about the chemical element. For other uses, see Chlorine (disambiguation).

"Cl" and "Cl2" redirect here. For other uses, see CL (disambiguation) and CL2 (disambiguation).

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, ₁₇Cl

Chlorine
Pronunciation	/ˈklɔːriːn, -aɪn/ ​(KLOR-een, -⁠eyen)
Appearance	pale yellow-green gas
Standard atomic weightAr°(Cl)
	[35.446, 35.457] 35.45±0.01 (abridged)
Chlorine in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson F ↑ Cl ↓ Br sulfur ← chlorine → argon
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
Phaseat 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
Triple point	172.22 K, ​1.392 kPa
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 P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 128 139 153 170 197 239
Atomic properties
Oxidation states	common: −1, +1, +3, +5, +7 +2, +4, +6
Electronegativity	Pauling scale: 3.16
Ionisation energies	1st: 1251.2 kJ/mol 2nd: 2298 kJ/mol 3rd: 3822 kJ/mol (more)
Covalent radius	102±4 pm
Van der Waals radius	175 pm
Spectral lines of chlorine
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)
Thermal conductivity	8.9×10−3 W/(m⋅K)
Electrical resistivity	>10 Ω⋅m (at 20 °C)
Magnetic ordering	diamagnetic
Molar magnetic susceptibility	−40.5×10−6 cm3/mol
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 v e
Main isotopes Decay abun­dance half-life(t1/2) mode pro­duct 35Cl 76% stable 36Cl trace 3.01×105 y β− 36Ar ε 36S 37Cl 24% stable
Category: Chlorine view talk edit | references

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 20th most abundant element in Earth's crust. These crystal 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.