Chlorine Element Facts

Chlorine In Test Tube

Chlorine In Test Tube (Photo: Ben Mills)


Data Zone

Classification: Chlorine is a halogen and a nonmetal
Color: greenish-yellow
Atomic weight: 35.453
State: gas
Melting point: -101 oC , 172 K
Boiling point: -34 oC , 239 K
Electrons: 17
Protons: 17
Neutrons in most abundant isotope: 18
Electron shells: 2,8,7
Electron configuration: 1s2 2s2 2p6 3s2 3p5
Density @ 20oC: 0.003214 g/cm3
Show more, including: Heats, Energies, Oxidation, Reactions, Compounds, Radii, Conductivities
Atomic volume: 22.7 cm3/mol
Structure: layers of Cl2 in solid
Specific heat capacity 0.48 J g-1 K-1
Heat of fusion 6.406 kJ mol-1 of Cl2
Heat of atomization 122 kJ mol-1
Heat of vaporization 20.41 kJ mol-1 of Cl2
1st ionization energy 1251.1 kJ mol-1
2nd ionization energy 2297.3 kJ mol-1
3rd ionization energy 3821.8 kJ mol-1
Electron affinity 349 kJ mol-1
Minimum oxidation number -1
Min. common oxidation no. -1
Maximum oxidation number 7
Max. common oxidation no. 7
Electronegativity (Pauling Scale) 3.16
Polarizability volume 2.2 Å3
Reaction with air none
Reaction with 15 M HNO3 mild, ⇒ HClOx, NOxCl, NOx
Reaction with 6 M HCl mild, ⇒ HOCl, Cl-
Reaction with 6 M NaOH mild, ⇒ OCl-, Cl-
Oxide(s) Cl2O, ClO2, Cl2O7
Hydride(s) HCl
Chloride(s) Cl2
Atomic radius 100 pm
Ionic radius (1+ ion)
Ionic radius (2+ ion)
Ionic radius (3+ ion)
Ionic radius (1- ion) 167 pm
Ionic radius (2- ion)
Ionic radius (3- ion)
Thermal conductivity 0.0089 W m-1 K-1
Electrical conductivity
Freezing/Melting point: -101 oC , 172 K

Safe drinking water

Safe Drinking Water: Image: Ionut_Cojocaru. In green areas everyone can get safe water. In red areas, at least 25 percent of people can’t get treated water. Yellow areas are intermediate. Before the routine use of chlorine in U.S. water supplies, typhoid fever claimed 25 000 fatalities each year. Today 98% of public water supplies are treated with chlorine or a chlorine compound. Typhoid fever now claims about one victim a year, on average. (4)


Carl Wilhelm Scheele, who discovered chlorine in 1774.

Discovery of Chlorine

Dr. Doug Stewart

Chlorine was first produced in 1774 by Carl Wilhelm Scheele in Sweden. Scheele collected the gas released by the reaction of pyrolusite [manganese dioxide] with spiritus salis – an alchemical term meaning spirit/breath of salt. [It was also known as muriatic acid and we now call it hydrochloric acid.] The new gas had, according to Scheele, “a very perceptible suffocating smell, which was most oppressive to the lungs… and gives the water a slightly acidic taste… the air in it acquires a yellow color…” (1)

Scheele also noted the high reactivity and the bleaching qualities of the new gas he had made: “…all metals were attacked… fixed alkali was converted into common salt… all vegetable flowers – red, blue, and yellow – became white in a short time; the same thing also happened with green plants… insects immediately died. (1)

Despite the accuracy of his observations, Scheele mistakenly thought the new gas was a dephlostiganated [* see below] form of muriatic acid.

The famous French chemist Antoine Lavoisier believed the new gas should be called oxymuriatic acid [an oxide of hydrochloric acid] based on the as yet undiscovered element murium. (2)

* The confusion about chlorine’s true identity was caused by the phlogiston theory; phlogiston had been accepted by chemists for most of the 1700s – until Lavoisier himself debunked it. Phlogiston was a ‘substance’ used to explain the then inexplicable. Conveniently, it had negative weight when it needed to, and ‘explained’ reactions such as rusting and burning.

Lavoisier was the architect of phlogiston’s downfall, showing that the chemistry of oxygen was a better explanation in chemical reactions than phlogiston was. (3)

By 1810 the scientific consensus was that the element we now call chlorine was actually a compound that contained oxygen. English chemist Sir Humphry Davy found that the consensus was wrong; he could not get the new yellow-green gas to react with a charcoal electrode, which made him believe it may not contain oxygen. In reactions with phosphorus and ammonia, he demonstrated the new gas did not contain oxygen. He used a huge, 2000 plate voltaic pile [battery] to see whether he could extract oxygen from the gas’s phosphorus and sulfur compounds, but again he found no oxygen. (1a)

In 1811, Davy concluded the new gas was in fact a new element. (1b) He named it chlorine, from the Greek word ‘chloros,’ meaning pale green or yellow-green.

Interesting Facts about Chlorine

  • The first chain reaction discovered was not a nuclear reaction; it was a chemical chain reaction. It was discovered in 1913 by Max Bodenstein, who saw a mixture of chlorine and hydrogen gases explode when triggered by light. The chain reaction mechanism was fully explained in 1918 by Walther Nernst.
  • Earth’s oceans contain a large amount of chlorine. If this chlorine were released as a gas, its weight would be 5x greater than Earth’s total current atmosphere. (Our oceans contain about 2.6 x 1016 metric tons of chlorine, mostly as sodium chloride.)
  • Chlorine is not only abundant in our oceans; it is the sixth most abundant element in Earth’s crust.
  • Exposure to small amounts of chlorine, even for a short time, can be deadly. Fatalities are expected at 1 part in a thousand chlorine in air (or sometimes at even lower concentrations). (5)
  • Chlorine is heavier than air. When released, it forms a poisonous blanket that drifts along with the wind. Chlorine was used as a chemical weapon in World War I, first in 1915 by the German army and then by the Western Allies. It was not as ‘effective’ as had been hoped, because chlorine is easily detected by its strong smell. It is also water soluble, and so soldiers could protect themselves from the worst of its effects by breathing through damp cloths.

Sodium Choride is table salt. You’ve run out? Here’s one way of getting more!

Chlorine made by reacting hydrochloric acid with potassium permanganate.

Appearance and Characteristics

Harmful effects:

Chlorine is a toxic gas that irritates the skin, the eyes and the respiratory system.


Chlorine is a greenish-yellow, diatomic, dense gas with a sharp smell (the smell of bleach).

It is not found free in nature as it combines readily with nearly all other elements.

Chlorine occurs in nature mainly as common salt (NaCl), carnallite [ KMgCl2.6(H20) ], and sylvite (KCl).

In its liquid and solid form it is a powerful bleaching, oxidizing and disinfecting agent.

Uses of Chlorine

Chlorine is used for producing safe drinking water.

Chlorinated compounds are used mostly for sanitation, pulp bleaching, disinfectants, and textile processing.

Chlorine is also used for the manufacture of chlorates and it is important in organic chemistry, forming compounds such as chloroform, carbon tetrachloride, polyvinyl chloride, and synthetic rubber.

Other uses of chlorine compounds include dyestuffs, petroleum products, medicines, antiseptics, insecticides, foodstuffs, solvents, paints and plastics.

Abundance and Isotopes

Abundance earth’s crust: 145 parts per million by weight, 85 parts per million by moles

Abundance solar system: 8 parts per million by weight, 0.3 parts per million by moles

Cost, pure: $0.15 per 100g

Cost, bulk: $ per 100g

Source: Chlorine gas is produced commercially by the electrolysis of sodium chloride (NaCl) from seawater or brine from salt mines.

Isotopes: Chlorine has 16 isotopes whose half-lives are known, with mass numbers 31 to 46. Naturally occurring chlorine is a mixture of its two stable isotopes 35Cl and 37Cl with natural abundances of 75.8% and 24.3% respectively.


1. Henry M. Leicester, Herbert S. Klickstein, A Source Book in Chemistry, 1400-1900., (1969) p111. Harvard University Press.
1a. Henry M. Leicester, Herbert S. Klickstein, A Source Book in Chemistry, 1400-1900., (1969) p241. Harvard University Press.
1b. Henry M. Leicester, Herbert S. Klickstein, A Source Book in Chemistry, 1400-1900., (1969) p257. Harvard University Press.
2. J.W. Mellor, A Comprehensive Treatise on Inorganic and Theoretical Chemistry., 1922, vol 2, Longmans, Green and Co., p21.
3. Antoine Lavoisier, Memoires de l’ Academie royale des sciences 1783., 1786, p505-538.
4. The Chlorine Tree.
5. OSHA, Occupational Safety and Health Guideline for Chlorine.

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  1. shailendrasinh chauhan says:

    very impressive content…
    nice web site…
    I’m having a question: though chlorine is poisonous, why it is used to produce safe drinking water???

    • It depends on the concentration. In high concentrations chlorine can kill us. When the concentrations are low it kills bugs but leaves us unharmed.

  2. anonymous says:

    I have chlorine for a project in science but i dont know any MINDBLOWING facts. Help?

  3. I love this site we are doing a class periodic table and everyone in the class got there own element and we are doing research about it and this site gave me a lot of the information i needed