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Chlorine General

Name:Chlorine Symbol:Cl
Type:Halogen Atomic weight:35.453
Density @ 293 K:0.003214 g/cm3 Atomic volume:22.7 cm3/mol

Chlorine was produced first in 1774 by Carl Wilhelm Scheele, who collected the gas released by the reaction of pyrolusite (manganese dioxide) with the substance we now call hydrochloric acid. It 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..." Scheele also noted the reactivity and 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 resulting gas was a compound that contained oxygen.

Sir Humphry Davy in 1810, however, found he could not get the new gas to react with a charcoal electrode, which caused him to believe it may not contain oxygen. In reactions with phosphorus and ammonia, he demonstrated the new gas could not contain oxygen. He used a huge, 2000 plate voltaic pile (battery) to see whether he could get oxygen out of the gas's compounds with phosphorus and sulfur, but again 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.

Chlorine States

State (s, l, g):gas
Melting point:172 K (-101 °C) Boiling point:239 K (-34 °C)

Chlorine Energies

Specific heat capacity: 0.48 J g-1 K-1 Heat of atomization:122 kJ mol-1
Heat of fusion:6.406 kJ mol-1 of Cl2 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

Chlorine Oxidation & Electrons

Shells:2,8,7 Electron configuration: [Ne] 3s2 3p5
Minimum oxidation number:-1 Maximum oxidation number:7
Min. common oxidation no.:-1 Max. common oxidation no.:7
Electronegativity (Pauling Scale):3.16 Polarizability volume:2.2 Å3

Chlorine Appearance & Characteristics

Structure:layers of Cl2 Color:greenish-yellow
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(H2O) ], and sylvite (KCl).

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


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. 

Chlorine Reactions

Reaction with air: none Reaction with 6 M HCl:mild, ⇒ HOCl, Cl-
Reaction with 15 M HNO3: mild, ⇒ HClOx, NOxCl, NOx Reaction with 6 M NaOH:mild, ⇒ OCl-, Cl-

Chlorine Compounds

Oxide(s):Cl2O, ClO2, Cl2O7 Chloride(s):Cl2

Chlorine Radius

Atomic radius:100 pm Ionic radius (1+ ion):pm
Ionic radius (2+ ion):pm Ionic radius (3+ ion):pm
Ionic radius (2- ion):pm Ionic radius (1- ion):167 pm

Chlorine Conductivity

Thermal conductivity:0.0089 W m-1K-1 Electrical conductivity:S cm-1

Chlorine Abundance & 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

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


Chlorine has 16 isotopes whose half-lives are known, with mass numbers 31 to 46. Of these, two are stable: 35Cl and 37Cl.

Chlorine Other


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.

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