Chlorine Element Facts

States | Energies | Electrons | Characteristics | Reactions & Compounds | Radius | Conductivity | Abundance & Isotopes
17
Cl
35.45
Chlorine
Chlorine In Test Tube (Photo: Ben Mills)
Classification:Chlorine is a halogen and a nonmetal
Atomic weight:35.453 g/mol
Density @ 20 oC:0.003214 g/cm3
Atomic volume:22.7 cm3/mol
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)

Scheele
Carl Wilhelm Scheele, who discovered chlorine in 1774.

Discovery of Chlorine


Author: Dr. Doug Stewart
Chlorine was first produced in 1774 by Carl Wilhelm Scheele.

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. 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.

States

State (s, l, g): gas
Melting point: 172 K   (-101 oC)

Boiling point: 239 K   (-34 oC)

Energies

Specific heat capacity: 0.48 J g-1 K-1
Heat of fusion: 6.406 kJ mol-1 of Cl2
1st ionization energy: 1251.1 kJ mol-1
3rd ionization energy: 3821.8 kJ mol-1
Heat of atomization: 122 kJ mol-1
Heat of vaporization: 20.41 kJ mol-1 of Cl2
2nd ionization energy: 2297.3 kJ mol-1
Electron affinity: 349 kJ mol-1

Oxidation & Electrons

Shells: 2,8,7
Minimum oxidation number: -1
Min. common oxidation no.: -1
Electronegativity (Pauling Scale): 3.16
Electron configuration: 1s2 2s2 2p6 3s2 3p5
Maximum oxidation number: 7
Min. common oxidation no.: 7
Polarizability volume: 2.2 Å3

Appearance & Characteristics

Structure: layers of Cl2
Hardness: mohs

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.
Color: greenish-yellow


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

Characteristics:
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:
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.

Reactions & Compounds

Reaction with air: none
Reaction with 15 M HNO3: mild, ⇒ HClOx, NOxCl, NOx
Oxide(s): Cl2O, ClO2, Cl2O7
Hydride(s): HCl
Reaction with 6 M HCl: mild, ⇒ HOCl, Cl-
Reaction with 6 M NaOH: mild, ⇒ OCl-, Cl-
Chloride(s): Cl2

Radius

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

Conductivity

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

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

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. Of these, two are stable: 35Cl and 37Cl. The most abundant isotope is 35Cl at 75.8%.


References

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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