Chlorine (Cl): Properties & Uses

Chlorine is a chemical element that belongs to the halogen family of the periodic table of elements. It can be found in great concentrations on earth, but due to its high reactivity, it is usually found in the compound form with the other elements. Perhaps the most familiar example of a chlorine compound is common salt or sodium chloride (NaCl). The elemental chlorine is highly electronegative, and therefore, highly reactive. This property accounts for its toxic nature which poses many difficulties to work with it in its elemental form.  Chlorine has a wide range of applications ranging from disinfectant to bomb manufacturing. It is available in the biggest repository on planet earth, the oceans, which makes it easily available and employable through several industries.

chlorine (1)

Discovery and Naming


Carl Wilhem Scheele

In 1774, Swedish pharmacist Carl Wilhem Scheele released a few drops of hydrochloric acid onto a piece of manganese dioxide. A greenish-yellow gas evolved from that chunk of manganese dioxide. However, he had no idea at the time that he had just discovered chlorine. Until an English chemist, Sir Humphrey Davy, recognized that the gas produced in the reaction was elemental chlorine, people were convinced that the gas was a compound of oxygen. Davy gave the element its name based on the Greek word “khloros,” in reference to its greenish-yellow colour. In 1810 he suggested the name “chloric gas” or “chlorine.” Since then, it was one of the most effective and economical germ-killers. Chlorine disinfectants destroy and deactivate a wide range of dangerous germs in homes, hospitals, swimming pools, hotels, restaurants, and other public places. Chlorine’s powerful disinfectant qualities come from its ability to bond with and destroy the outer surfaces of bacteria and viruses. In fact, it was first used in 1847 as a germicide to prevent the spread of “childbed fever” in the maternity wards of Vienna General Hospital in Austria.


Sir Humphrey Davy

Isotopes of Chlorine

Chlorine has 25 isotopes with mass numbers ranging from _{ }^{ 28 }{ Cl } to _{ }^{ 52 }{ Cl }, out of which only two are stable, _{ }^{ 35 }{ Cl }_{ }^{ 37 }{ Cl }. These isotopes are usually produced in stars by the process of oxygen and silicon burning. Among all its radioactive isotopes, _{ }^{ 36 }{ Cl } has the longest half-life of  301000 years. However, all other radioactive isotopes have a half-life of less than an hour. _{ }^{ 36 }{ Cl } decays further to a stable isotope of sulphur by the process of electron capture. It can also be produced in the laboratory by neutron activation. However, _{ }^{ 36 }{ Cl } prepared in the laboratory can have a half-life  ranging from {3.0 × 10 }^{ 5 }{ years} to 37.2 minutes.


Properties of Chlorine



Physical Properties


Chlorine Gas Leak

Chlorine belongs to the halogen group of p-block elements of the periodic table with atomic no. 17 and atomic mass 35.43 u. Elemental chlorine  ({ Cl }_{ 2 }) is a yellow-green poisonous gas at room temperature which is 2.5 times heavier than air and has a pungent odour similar to bleach even at very low concentrations. It liquefies at the temperature of -34.05ºC (boiling point) and forms yellow coloured crystals on further lowering the temperature to -100ºC (melting point). It has the density of 0.0028985 gram per cubic centimetre at 20ºC. Chlorine is more soluble in water than other aqueous solutions. The yellow colour of chlorine corresponds to the electron transition between the highest occupied antibonding molecular orbital and the lowest vacant antibonding molecular orbital. Therefore, when we lower the temperature up to -195ºC chlorine appears almost colourless.

Chemical Properties


Chlorine has an electronic configuration of [Ne] { 3s }^{ 2 }{ 3p }^{ 5 }. It is the second most reactive non-metallic element after fluorine in the periodic table. Like other elements of the halogen family, chlorine also takes one electron to reach its optimal electronic configuration and thereby form chloride ion. Chlorine can take part in various compound formation by sharing one to seven electrons of its valence shell electrons. Therefore, it can exist in diverse oxidation states, for example, in the oxides of chlorine, hypochlorites have (+ 1) oxidation state, chlorates have (+ 5) oxidation state, and perchlorates have (+ 7) oxidation state. Chlorine prefers to make polar ionic bonds with most of the other elements.



When it comes to the compound formation with other halogen compounds, chlorine shows some unusual characteristics. While forming a compound with fluorine, such as ClF and {ClF}_{3}, it shows ionic character by itself being anion. Whereas, while forming compounds with iodine, such as {ICl}_{3} and ICl, it shows some ionic character to the bond, acting as a cation. With other halogen elements, it takes parts in covalent bonding for compound formation. Chlorine is very reactive, combining directly with most elements but only indirectly with nitrogen, oxygen, and carbon. Excess chlorine in the presence of ammonia salts forms the very explosive nitrogen trichloride, {NCl}_{ 3 }. Hypochlorites react with ammonia to produce the chloramines {NH}_{ 2 }{ Cl } and {NHCl}_{ 2 }.

3 {Cl}_{ 2 }+4 {NH}_{ 3 } {NCl}_{ 3 }+3 {NH}_{ 4 }{ Cl }

Compounds of Chlorine

Chemists began experimenting with chlorine and chlorine compounds in the 18th century. They learned that chlorine has an extraordinary ability to extend a chemical bridge between various elements and compounds that would not otherwise react with each other. Chlorine is one of the most abundant, naturally occurring chemical elements. It plays a significant role in the manufacture of thousands of products that we depend upon every day. Let’s discuss a few of its compounds.

1. Hydrochloric acid


Hydrochloric acid (HCl) is a colourless, corrosive, and a strong mineral acid with many industrial uses. When it reacts with an organic base it forms a hydrochloride salt. It was historically produced from rock salt and green vitriol and later from treating the chemically similar common salt (NaCl) with concentrated sulfuric acid( { H }_{ 2 }{ SO }_{ 4 }).

NaCl + { H }_{ 2 }{ SO }_{ 4 } ⟶  { NaHSO }_{ 4 } + HCl

The above reaction takes place at 150ºC. On increasing the temperature further up to 500ºC-600ºC, sodium chloride and sodium bisulphate also react to form hydrochloric acid.

NaCl + { NaHSO }_{ 4 } ⟶  { Na }_{ 2 }{SO }_{ 4 }  + HCl

Hydrochloric acid is also produced naturally by our stomach to digest food. It is used in the metal industry to process steel, the material of choice for suspension bridges and cars and trucks. Hydrochloric acid is also used in the production of batteries, photoflash bulbs and fireworks. It’s even used to process sugar and make gelatin. However, hydrochloric acid is more acidic than hydrofluoric acid due to the presence of stronger hydrogen bonding in HF that does not break easily and hence does not form ions.

2. Common Salt (NaCl)

Common salt is the most abundant repository of chlorine on earth. A large amount of chlorine is produced with the help of mineral salts found in the ocean water. Electricity is the tool used to electro-chemically split NaCl, releasing Cl for its many chemical uses. Chemical engineers design systems to make chlorine gas bubble out of salty, electrified water. The gas is captured and cooled down so much that it is liquefied. NaCl is essential to life on earth. It is a necessary ingredient in the diets of people and animals. It plays a key role in the manufacture of thousands of products we depend on every day, including volleyballs, computers, cars, pool chemicals, medicines and cosmetics.

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3. Chlorine organic compounds


Chlorine usually forms covalent bonds with carbon. It generally goes under substitution or addition reactions with hydrocarbons. In saturated hydrocarbons, chlorine replaces hydrogen, either entirely or partially, to form chlorinated hydrocarbons and hydrogen chloride. Chlorine goes under free-radical electrophilic substitution with alkanes and aryl alkanes. Many of chloro-organic compounds can be found in biomolecules and the majority of chloro-hydrocarbons such as Chloromethane can be found in the atmosphere due to the biological decomposition of other organic molecules.


Friedel Crafts mechanism

Uses of Chlorine

1. Water Treatment

swimming by Kuo Zhang on Dribbble

Chlorine is widely used to keep the swimming pools clean. As it can not be used in its elemental form for this purpose, people make use of two of its compounds, sodium hypochlorite (bleach) and calcium hypochlorite. Either of these two chemicals, when mixed with water, forms a weak acid called hypochlorous acid that kills bacteria like salmonella and E. coli. However, too much exposure to hypochlorous acid brings harm to the human body also, therefore, it is necessary to frequently monitor the pH levels of swimming pools.

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Swimming Pool Cleaning Kit

Chorine does not only helps in keeping the water clean, but it also helps in wastewater treatment. Wastewater disinfection is applied to protect humans against exposure to waterborne pathogenic microorganisms. It also helps in preventing aquatic pollution by preventing the accumulation of toxic microorganisms in fish, shellfish and other aquatic organisms. Chlorine kills bacteria by attacking the lipids in their cell walls and destroying the pathogen’s structure. When this happens, the chemicals can get inside the bacteria and kill their enzymes, ultimately destroying the bacteria’s mechanisms to function properly. However, it can also cause the formation of mutagenic/carcinogenic and toxic by-products that are potentially harmful to human and aquatic organisms.


 2. Automotive Industry


Perhaps the major demand for chlorine market around the world is driven by the automotive industry. It is used in nylon manufacturing for the several parts of a car, such as safety belts, airbags, bumpers, mats, dashboards, coolants and anti-freezers. Chlorine is also used in boat hulls, nets and lines for fishing boats as well as corrosion-resistant paint. Even the high-grade lubrication oils, gasoline additives, electrical components, windows on buses and brake fluids are made up using chlorine.

3. Health Care


The tendency of chlorine to act as a disinfectant, and being present in such abundant volumes, makes it a preferable choice for many industries including health care. Chlorine products are effective in reducing many of today’s infection risks. Both liquid (sodium hypochlorite solution, e.g., chlorine bleach) and solid (calcium hypochlorite) are available in hospitals and when used according to product specifications, they do not stain or leave toxic residues. They are inexpensive chemicals and non-toxic at concentrations that disinfect. In hospitals, chlorine is primarily used in making sterile packaging, surgical instruments, laboratory reagents and even prescription eyewear.


Chlorine chemistry plays a supporting role in drug synthesis. For example, a hydrochloric acid solution may be used to control pH during the manufacturing process, or chlorinated solvents may be used as separating or purification agents. Frequently, large and complex drug molecules are synthesized from smaller “intermediate” molecular fragments. It is widely used in the manufacture of several drugs, such as antibiotics, antihistamines, pain relievers, aspirin and even used in cancer treatments.

4. Electronics Industry

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Chlorine tendency to form polyvinyl chloride, which is fire repellants, makes it useful in making wire coatings for computer cables. It is also used in the manufacture of computer disks and other semiconductor devices.


5. Metal Industry

Chlorine is a major element used in various metallurgical processes for the extraction of nonferrous elements from their ores and concentrations. The use of chlorine in metal extraction processes through pyro or pyro and hydrometallurgy routes has gained considerable attention in recent years. Chlorine compounds such as hypochlorous acid, chlorine gas, and several alkyls and alkaline compounds of chlorine have proved very usefully in the extraction of many silicate ores, oxides and several sulphides. Because of their high reactivity at a moderate temperature, selectivity in the chlorination of the desired metal values, and their easy availability with low cost, these chlorinating agents are being widely used in the ores and minerals for preparation of pure metal chlorides and the recovery of metal values from the scrap and other wastes.


Chlorination Plants In Various Metal Industries

6. Construction


Chlorine also plays an essential role in the construction of buildings and making our homes beautiful. From the very fundamental necessities, such as nuts and bolts, to the fanciest decors, it plays an important part in their manufacturing. Chlorine can be found in most of the household items, such as carpets, PVC pipes, floorings, paints, coatings, wire insulations, etc. It helps to protect you from the elements with durable siding, and lets you enjoy the outdoors with products like garden hoses and lawn furniture.

File:An Irrigation sprinkler watering a garden.gif - Wikimedia Commons

7. Defence

bulletproof vest

The soldiers and law enforcers are reliable on chlorine for their safety during their operations. Protective equipment such as bullet-resistant vests, and tools for intelligence including surveillance cameras, all use chlorine chemistry for their manufacture. Also, medical equipment such as blood bags and tubing are made with chlorine and are crucial in protecting the lives of soldiers and police officers. It is also used in the manufacture of other protective gears, such as helmets, parachutes, water repellant fibres, and shatter-resistant glasses. Chlorine also helps in guarding our skies by playing an important role in the manufacture of titanium aircraft, jet engines, and missiles.

The Next Generation F-15 Is Packed With Missiles

8. Miscellaneous Uses

Chlorine is also used in the manufacture of various equipment that makes extreme sports possible. Various types of equipment used for such recreational activities make use of chlorine for their reliability. For instance, nylon ropes made for rock climbing and raft manufacturing are made up of chlorine-based polymers. It is also used in the manufacture of neoprene wetsuits, inflatable rafts and even jet skis. Most essential equipment required for mountaineering such as sleeping bags and jackets has chlorine as a major manufacturing ingredient.

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Health Aspects


Although chlorine can be found almost anywhere around oneself, its uncontrolled exposure can result in severe health conditions. For instance, low concentrations of chlorine can cause itching and burning of the eyes, nose, throat and respiratory tract. At high concentrations, chlorine is a respiratory poison. Irritant effects become severe and may be accompanied by tearing of the eyes, headache, coughing, choking, chest pain, shortness of breath, dizziness, nausea, vomiting, unconsciousness and death. Bronchitis and accumulation of fluid in the lungs (chemical pneumonia) may occur hours after exposure to high levels. Liquid, as well as vapour contact, can cause irritation, burns and blisters. Ingestion can cause nausea and severe burns of the mouth, oesophagus and stomach. Prolonged or repeated overexposure may result in any or all of the effects reported for acute exposure (including pulmonary function effects).


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