Chlorine

Chlorine, ₁₇Cl
General properties
Pronunciation	/ˈklɔːriːn, -aɪn/ (klohr-EEN-,_---eyen)
Appearance	pale yellow-green gas
Standard atomic weight (Ar, standard)	[35.446, 35.457]
Chlorine in the periodic table
	sulfur ← chlorine → argon
Atomic number (Z)	17
Group	group 17 (halogens)
Period	period 3
Block	p-block
Element category	reactive nonmetal
Electron configuration	[Ne] 3s2 3p5
Electrons per shell	2, 8, 7
Physical properties
Phase at STP	Cl: Gas
Melting point	171.6 K (−101.5 °C, −150.7 °F)
Boiling point	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
Critical point	416.9 K, 7.991 MPa
Heat of fusion	(Cl2) 6.406 kJ/mol
Heat of vaporization	(Cl2) 20.41 kJ/mol
Molar heat capacity	(Cl2); 33.949 J/(mol·K)
Atomic properties
Oxidation states	−1, +1, +2, +3, +4, +5, +6, +7 (a strongly acidic oxide)
Electronegativity	Pauling scale: 3.16
Ionization 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	Cl: Primordial
Crystal structure	orthorhombic
Speed of sound	206 m/s (gas, at 0 °C)
Thermal conductivity	8.9×10−3 W/(m·K)
Electrical resistivity	>10 Ω·m (at 20 °C)
Magnetic ordering	diamagnetic
Magnetic susceptibility	−40.5·10−6 cm3/mol
CAS Number	(Cl2) 7782-50-5
History
Discovery and first isolation	Carl Wilhelm Scheele (1774)
Recognized as an element by	Humphry Davy (1808)
Main isotopes of chlorine
ε	36S
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Chlorine (chemical symbol Cl) is a chemical element. Its atomic number (which is the number of protons in it) is 17, and its atomic mass is 35.45. It is part of the 7th column (halogens) on the periodic table of elements.

Chlorine gas in a tube

Properties

Physical properties

Chlorine is a very irritating and greenish-yellow gas. It has a strong, bleach-like smell. It is toxic and bad for you. It can be made into a liquid when cooled. It is heavier than air.

Chemical properties

Chlorine is highly reactive. It is more reactive than bromine but less reactive than fluorine. It reacts with most things to make chlorides. It can even burn things instead of oxygen. It dissolves in water to make a mixture of hypochlorous acid and hydrochloric acid. The more acidic it is, the more chlorine is made; the more basic it is, the more hypochlorous acid (normally turned into hypochlorite) and hydrochloric acid (normally turned into chlorides) are there. Chlorine reacts with bromides and iodides to make bromine and iodine.

Chlorine compounds

Chlorine exists in several oxidation states: -1, +1, +3, +4, +5, and +7. The -1 state is most often in chloride. Chlorides are not reactive. Compounds containing chlorine in its +1 oxidation state are hypochlorites. Only one is common. They are a strong oxidizing agent, as are all + oxidation state compounds. +3 is in chlorites. +4 is in chlorine dioxide, a common chlorine compound that is not a chloride. +5 is in chlorates. +7 is in perchlorates. Hypochlorites are most reactive, while perchlorates are the least reactive.

Many organic compounds have chlorine in them. Freon has chlorine in it. PVC (poly-vinyl chloride), a common plastic, has chlorine in it.

Chlorine oxides can be made, but most of them are very reactive and unstable.

Chloroform is 89% chlorine by molecular weight
PVC pipe, a plastic that has chlorine in it
Sodium chloride
Potassium chlorate
Potassium perchlorate

Occurrence

Chlorine is not found as an element. Sodium chloride is the most common chlorine ore. It is in the ocean (sea salt) and in the ground (rock salt). There are some organic compounds that have chlorine in them, too.

Preparation

It is made by electrolysis (the passing of electricity through a solution to make chemical reactions happen) of sodium chloride. This is known as the chloralkali process. It can also be made by reacting hydrogen chloride with oxygen and a catalyst. It can be made in the laboratory by reacting manganese dioxide with hydrochloric acid. It is made when sodium hypochlorite reacts with hydrochloric acid. This is a dangerous reaction that can happen without anyone knowing.

Uses

For water purification

As of 2021, the main use of chlorine is for bleach. It is also added to water, as a way of purifying it. Chlorine is both very reactive, and very poisonous. It will act as a disinfectant: if it is added to water, it will kill off bacteria and other organisms. Swimming pools are often filled with water that has been treated that way.

As a chemical weapon

Germany used chlorine as a chemical weapon in the First World War. They used it at the Second Battle of Ypres in 1915.^[5]^[6] According to soldiers, which were present at the battle, the chlorine smelled like a mixture of pepper and pineapple. It also tasted metallic and stung the back of the throat and chest. Chlorine reacts with water in the mucosa of the lungs to form hydrochloric acid. Hydrochloric acid will destroy living tissue. It often kills. Gas masks with activated charcoal or other filters can protect the respiratory system. This makes chlorine gas much less deadly than other chemical weapons. German scientist Fritz Haber of the Kaiser Wilhelm Institute in Berlin was the first to use it. Together with IG Farben, he developed methods of how to use chlorine gas against an entrenched enemy.^[7] Chlorine is heavier than air, so it will stay in the trenches. On 22nd April, 1915, German forces attacked the French army. With 150 tonnes (150 long tons; 170 short tons) of chlorine, they only killed about 1.200 French soldiers.^[8] For this reason, chlorine was soon replaced with the more deadly phosgene and mustard gas.^[9]

Because it is easily available, chlorine is still used as a chemical weapon in war. That way, it has been used in the Syrian civil war.^[10] ^[11]^[12] It has also been used in an improvised explosive device in Iraq, in 2015.^[13]

Other uses

Chlorine is used to make many compounds that are important: both chloroform and carbon tetrachloride contain chlorine.

History

It was discovered in 1774 by Carl Wilhelm Scheele who thought it had oxygen in it. Chlorine was named in 1810 by Humphry Davy who insisted it was an element. The US made all water chlorinated (added chlorine to water) by 1918.

Safety

It is poisonous in large amounts and can damage skin. When it is inhaled (breathed in), it irritates the lungs, eyes, and skin badly. It can cause fire with some things because it is very reactive. It is heavier than air, so it can fill up enclosed spaces.

ChlorineChemical Compounds Media

Carl Wilhelm Scheele, discoverer of chlorine
Chlorine, liquefied under a pressure of 7.4 bar at room temperature, displayed in a quartz ampule embedded in acrylic glass
Gaseous chlorine stored inside a 500-mL water bottle. It is not recommended to store chlorine in this manner.
Solid chlorine at −150 °C
Structure of solid deuterium chloride, with D···Cl hydrogen bonds
Hydrated nickel(II) chloride, NiCl2(H2O)6
Yellow chlorine dioxide (ClO2) gas above a solution of hydrochloric acid and sodium chlorite in water, also containing dissolved chlorine dioxide
Structure of dichlorine heptoxide, Cl2O7, the most stable of the chlorine oxides
ChlorideionDvdW
HypochloriteDvdW