Chlorine Element- Definition, Properties, Reactions, Uses, Effects

The element Chlorine is the halogen located in group 17 in the periodic table. Chlorine is the chemical element that constitutes about 0.017 percent of the earth’s crust. Chlorine is a toxic, corrosive gas that is greenish-yellow and irritating to the eyes and respiratory system.

There are lots of use and benefits of chlorine which we will discuss later. Firstly, let us learn some important facts and history about the element.

The Symbol of the element Chlorine is Cl.

Chlorine (Cl) Element
Chlorine (Cl) Element

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History of Chlorine Element

Chlorine name is derived from the Greek word chloros, which means greenish-yellow. For thousands of years, people have used rock salt (also known as common salt or sodium chloride). It is the main component of the salts dissolved in seawater, which was obtained by evaporation in ancient Egypt.

History of Hydrochloric Acid

Initially, Johann Rudolf Glauber, a German chemist, created the spirit of salt in 1648 by heating moist salt in a charcoal furnace and condensing the fumes in a receiver. Later, by heating salt with sulfuric acid, he obtained the same product, now known as hydrochloric acid.

Later, Carl Wilhelm Scheele, in Uppsala, Sweden, created the gaseous element in 1774 by heating hydrochloric acid with the mineral pyrolusite, which is naturally occurring manganese dioxide, MnO2. As a result, a dense, greenish-yellow gas was produced, which had a choking odor and dissolved in water to form an acid solution. Finally, he observed that it bleached litmus paper and faded the colors of flowers and leaves. Later, Humphry Davy proved it to be an element in 1810.

Occurrence of Chlorine Element

Except for very small amounts of free chlorine (Cl) in volcanic gases, chlorine is only found in chemical compounds. It accounts for 0.017 percent of the Earth’s crust. Natural chlorine consists of two stable isotopes: chlorine-35 (75.53 percent) and chlorine-37 24.47 percent).

Abundance of Chlorine

The most common chlorine compound is sodium chloride, which occurs naturally as crystalline rock salt that is often discolored by impurities. Sodium chloride is also found in seawater, with an average concentration of about 2% of that salt. Additionally, blood and milk contain trace amounts of sodium chloride. Also, the stomach contains free hydrochloric acid.

Chlorine-containing minerals are:

MineralsChemical Formula
Bischofite   MgCl∙6H2O
Carnallite KCl∙MgCl∙6H2O
Kainite KCl∙MgSO∙3H2O
Chlorapatite Ca5(PO4)3Cl
Sodalite Na8Al6Si6O24Cl2
Chlorine in minerals

Physical Properties of Chlorine Element

Basically, at room temperature and atmospheric pressure, chlorine is a greenish yellow gas. It weighs two and a half times as much as air. Also, at room temperature, the gas is easily liquefied by cooling or pressures of a few atmospheres. Accordingly, chlorine can have the oxidation numbers +1, +3, +4, +5, +6, and +7.

Electronic Configuration[Ne]3s23p5
Block, Period and Group in periodic tablep-block, Group-17, Period-3
Atomic Number17
Atomic Weight35.48
State at 20 °CGas
Melting Point-101.5 °C, -150.7 °F, 171.7 K
Boiling Point-34.04 °C, -29.27°F, 239.11 K
Density0.0029 g/cm3
Atomic radius (non-bonded)1.75  Å
Covalent Radius 1.00  Å
Electronegativity3.16 (Pauling Scale)
Electron Affinity348.575 KJ/mol
First Ionization Energy1251.19 KJ/mol
Crystal StructureOrthorhombic
Critical Temperature416.9 K
Atomic, Physical, and Periodic Properties

Reaction of Chlorine Element: Chemical Properties

Chiefly, chlorine’s chemical properties and reactivity are intermediate between the halogen elements fluorine and bromine.

The halogen family’s bond energies do not decrease from fluorine to iodine. It is due to fluorine molecules’ small size, low electric polarization, and lack of vacant d-orbitals for chemical bonding.

With increasing overlapping orbitals, the gradual decrease in bond energy from Cl2 to I2 results in poorer overlap accordingly. Hence it demonstrates that chlorine chemistry differs from fluorine chemistry. Also, it has positive oxidation states.

Chlorine Reaction with Water

Typically, chlorine-water reactions are used to disinfect but chlorine is only slightly soluble in water, reaching a maximum solubility at 49° F. Its solubility then decreases until it reaches 212° F. Consequently, it forms crystalline hydrates (usually Cl2) and becomes insoluble at temperatures below that range. Generally, it forms hypochlorous acid between those temperatures ( HOCl ). This is the primary reaction applicable in the disinfection and bleaching of water and wastewater.

Primary Reaction used for bleaching and water disinfection: Cl2 + H2O → HOCl + HCl

Chlorine decomposes water at boiling temperature of water: 2Cl2 + 2H2O → 4HCl + O2

Chlorine Reaction with Hydrogen

In sunlight or high temperatures, Hydrogen and Chlorine reacts rapidly and violently. Otherwise, the reaction will be slow.

H2 +Cl2 → HCl

Chlorine Reaction with Halide Ions

Chlorine participate in displacement reactions, which occur when a more reactive halogen displaces a less reactive halide ion from an aqueous solution. chlorine has the ability to displace bromide and iodide ions. It cannot, however, displace fluoride ions. When chlorine reacts with sodium bromide, the chlorine ions gets displaced, resulting in sodium chloride and bromine.

Cl2 (aq) +NaBr (aq) → 2NaCl (aq) + Br2 (aq)

Chlorine Reaction with Sodium

Chlorine reacts with sodium to form sodium chloride, a common component that is essential to our health and well-being. This is an example of a redox reaction that results in the formation of an ionic compound.

Cl2 + 2Na → 2NaCl

Chlorine Reaction with Alkalis

Chlorine in Cold Alkali (15°C)

The reaction between chlorine and an alkali, such as sodium hydroxide, produces sodium chlorate(I). This is used to treat wastewater once again, but it is also an active ingredient in household bleach.

Cl2 (g) + NaOH (aq) → NaClO (aq) + NaCl (aq) + H2O (l)

Chlorine atoms are both oxidized and reduced to form sodium chlorate(I) and sodium chloride. This is yet another disproportionation reaction.

Chlorine in Hot Alkali (70°C)

When we add chlorine and hot concentrated aqueous sodium hydroxide a different type of disproportionation reaction takes place:

3Cl2 (aq) + 6NaOH (aq) → 5NaCl (aq) + NaClO3 (aq) + 3H2O(l)

Oxidation no. of Chlorine : (0) to (-1 ) and (0) to (+5)

Chlorine Reaction with Metals

Metals react with chlorine to form metal chlorides and also the majority of which are soluble in water. AgCl and PbCl2 are examples of insoluble compounds. At temperatures below 230°F, gaseous or liquid chlorine does not affect metals such as iron, copper, platinum, silver, and steel.

Cl2 + Fe → FeCl2

Half Reactions:

Fe → Fe+2 + 2e

Cl2 + 2e → 2Cl

Also read out the reaction of chloride ions

Uses of Chlorine Element

1. Chlorine in water treatment:

Chlorine is used in water and wastewater disinfection (the removal of harmful microorganisms). Generally, it is almost exclusively used in the United States. Also, in 1908, sodium hypochlorite (NaOCl) was used to disinfect drinking water for the first time:

NaOCl + H2O → HOCl + NaOH

Diseases caused by contaminated water further decreased dramatically after the widespread use of sodium hypochlorite to disinfect water. It is effective at lower concentrations and is less expensive than other methods. The pH of the treated water is corrected after chlorination, in addition to any acids that may have been present in the original water. Therefore, this is typically accomplished by adding calcium hydroxide to the water.

2. Polyvinyl Chloride (PVC):

Polyvinyl Chloride is a plastic that is widely manufactured around the world and accounts for nearly one-third of global chlorine consumption. Altogether it is produced by first converting EDC (ethylene dichloride) into vinyl chloride, the basic unit for PVC. Hence, the monomers of vinyl chloride combine to form a polymer. As a result, PVC becomes malleable at high temperatures, making it flexible and ideal for a variety of applications ranging from pipes to clothing.

However, PVC is carcinogenic. When inhaled in gaseous form, it can harm the lungs, the body’s blood circulation, and the nervous system. Moreover, you should also be aware of the issues associated with the disposal of chlorinated polymers such as PVC. Poisonous products such as phosgene (COCl2) and dioxins are formed when these are burned at too low a temperature.

3. Bleaching:

Certainly, paper is one of the most widely used materials on the planet. However, before the wood can be turned into paper, it must first be converted into pulp (separated fibrous material). The color of this pulp ranges from light to dark brown. Chlorine helps bleach the pulp, making it a bright, white color that is appealing to consumers. Depending on the nature of the pulp, the process may involve several steps.

Most chlorine-smelling household bleach is a combination of sodium chloride and sodium chlorate(I) (sodium hypochlorite).

Sodium chlorate(I) is sometimes abbreviated as NaClO and other times as NaOCl. It is a strong oxidizing agent that bleaches things by oxidizing a variety of colored substances.

4. Insecticides:

These are both chlorinated hydrocarbons that are effective but long-lasting insecticides but unfortunately, they degrade slowly in the environment and accumulate in food chains.

These insecticides’ use is now restricted.

Chlorine is used to produce high-purity hydrochloric acid, extract titanium by forming titanium tetrachloride (TiCl4), and remove the tin from the old tinplate. Chlorine reacts with scrap aluminum or with aluminum oxide and carbon to produce anhydrous aluminum chloride (AlCl3). Chlorine is also used in the synthesis of silicon materials, such as silicon tetrachloride (SiCl4) and methyl chloride (CH3Cl). Chlorine is used directly or indirectly as an intermediate in many industrially important organic syntheses.

Health and Environmental Effects of Chlorine Element

Most chlorine exposures cause adverse health effects within seconds to minutes. The severity of chlorine-induced signs and symptoms will vary depending on the amount, route, and duration of exposure.

Health Effects due to Chlorine

  • Chlorine is used in water and wastewater treatment plants to reduce the levels of microorganisms in the water that can spread disease to humans (disinfection).
  • Breathing small amounts of chlorine for brief periods harms the human respiratory system. Coughing and chest pain are common side effects, as is water retention in the lungs. Chlorine irritates the skin, eyes, and respiratory system. These effects are unlikely to occur at chlorine levels commonly found in the environment.
  • The majority of chlorine exposures occur through inhalation. Signs and symptoms may progress to chest tightness, wheezing, dyspnea, and bronchospasm at higher levels of exposure. Severe exposures can cause noncardiogenic pulmonary edema that can last for several hours.
  • Ingestion of chlorine dissolved in water (e.g., sodium hypochlorite or household bleach) causes gastrointestinal tissue damage.

Environmental Effects of Chlorine

Although chlorine does not normally harm the environment, it quickly combines to form chemicals such as dioxins, which pollute water, contaminate fish, and transfer to humans and larger animals that eat the fish. This is known as biomagnification, and it occurs as levels of accumulated substances concentrate in animals higher up the food chain.

  • It reacts with inorganic materials in water to form chloride salts, and it reacts with organic materials in water to form chlorinated organic chemicals.
  • Chlorine is unlikely to move through the ground and enter groundwater due to its reactivity.
  • Also, this is unlikely to be stored by plants or animals. However, laboratory studies show that repeated exposure to chlorine in the air can harm an animal’s immune system, blood, heart, and respiratory system.
  • At low concentrations, chlorine harms the environment. Chlorine is particularly harmful to organisms that live in water and soil.

Toxicity classification by WHMIS 1988

Class D1A: Very toxic, Class E: Corrosive, Class A: Compressed gas

Class D1A, is the level of a substance that can damage a life form. Toxicity or even death can result from exposure to products affixed with this class of gas. Also acute toxicity can be the result of oral exposure, dermal exposure, and inhalation.

Cylinders storing compressed gas, liquefied gas, refrigerated liquefied gas, or dissolved gas can be dangerous. The cylinders will explode under heat.

The corrosive damage not only can this affect the skin and eyes, but also your workspace. In addition, some corrosive products can damage aluminum and steel, creating an unsafe environment.

Safety Measures

Before attempting a rescue, precautions are before ensuring your safety (e.g. wear appropriate protective equipment).

  • In case of inhaling, get the victim some fresh air. Maintain a comfortable breathing position at rest. If breathing becomes difficult, emergency oxygen should be administered by trained personnel. The onset of pulmonary edema symptoms may be delayed. Accordingly, call a Poison Control Center or a doctor right away. Further treatment is required immediately.
  • If chlorine comes in contact with skin, flush the part for 5 minutes with lukewarm, gently flowing water. Consult a doctor if the irritation or pain persists.
  • In case Liquefied gas comes in contact quickly remove the victim as soon as possible from the source of contamination. DO NOT TRY TO REWARM or RUB THE AFFECTED AREA ON THE SPOT. Remove any clothing or jewelry that may be impeding circulation. Remove the rest of the garment after carefully cutting around clothing that sticks to the skin. Cover the affected area loosely with a sterile dressing.
  • If gas comes in eye contact, flush the contaminated eye with lukewarm, gently flowing water for 5 minutes while keeping the eyelid open. If the irritation or pain persists, consult a doctor.
  • Avoid direct contact with liquefied gases and if necessary, put on chemically protective gloves. Immediately and briefly wash the eyes with lukewarm, gently flowing water. DO NOT ATTEMPT TO REWARM. Cover both eyes with a sterile dressing. DO NOT ALLOW THE VICTIM TO DRINK OR SMOKE.


  • Immediately evacuate the area. Isolate the danger zone. If ventilation is inadequate, vapor or gas can accumulate in dangerous amounts in low-lying areas, particularly inside confined spaces. Remove or isolate incompatible and potentially hazardous materials.
  • Wear chemical safety goggles to protect your eyes and face. A face shield (along with safety goggles) will work the best.
  • Immediately evacuate the area. Isolate the danger zone. If ventilation is inadequate, vapor or gas can accumulate in dangerous amounts in low-lying areas, particularly inside confined spaces. Remove or isolate incompatible and potentially hazardous materials.
  • Wear chemical safety goggles to protect your eyes and face. A face shield (along with safety goggles) will work the best.
  • Immediately evacuate the area. Isolate the danger zone. If ventilation is inadequate, vapor or gas can accumulate in dangerous amounts in low-lying areas, particularly inside confined spaces. Remove or isolate incompatible and potentially hazardous materials.
  • Wear chemical safety goggles to protect your eyes and face. A face shield (along with safety goggles) will work the best.
  • Wear chemical protective clothing, such as gloves, aprons, and boots, to protect your skin. Some operations require coveralls or long-sleeved shirts and pants. Wear a full-body encapsulating suit with chemical protection and a self-contained breathing apparatus (SCBA).
  • Do not apply to ultra-thin neoprene rubber gloves (0.3 mm or less).

Have a look at the guide for safety and hazards

For immediate help:

Centers for Disease Control and Prevention Public Response Hotline (1-888-246-2675)

Agency for Toxic Substances and Disease Registry (1-888-422-8737)

Regional Poison Control Center (1-800-222-1222)


  3. Sconce, J.S. Chlorine: Its Manufacture, Properties, and Uses. Reinhold Corporation, 1962.
  4. Stringer, Ruth, and Paul Johnston. Chlorine and the Enviroment. Norwell: Kluwer Academic, 2001.
  10. Chlorine. In: Sifton DW (Ed.), Physicians’ Desk Reference Guide to Biological and Chemical Warfare Response, 1st ed. (pp. 48-49). Montvale, NJ: Thomson/Physicians’ Desk Reference, 2002.
  12. Agency for Toxic Substances and Disease Registry. 2002. ToxFAQs for Chlorine. Division of Toxicology, U.S. Department of Health and Human Services. Public Health Service: Atlanta, GA.

About Author

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Jyoti Bashyal

Jyoti Bashyal, a graduate of the Central Department of Chemistry, is an avid explorer of the molecular realm. Fueled by her fascination with chemical reactions and natural compounds, she navigates her field's complexities with precision and passion. Outside the lab, Jyoti is dedicated to making science accessible to all. She aspires to deepen audiences' understanding of the wonders of various scientific subjects and their impact on the world by sharing them with a wide range of readers through her writing.

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