Periodic Table > Chlorine
 

Terminology


Allotropes
Some elements exist in several different structural forms, these are called allotropes.


For more information on Murray Robertson’s image see Uses and properties facts below.

 

Fact box terminology


Group
Elements appear in columns or ‘groups’ in the periodic table. Members of a group typically have similar properties and electron configurations in their outer shell.


Period
Elements are laid out into rows or ‘periods’ so that similar chemical behaviour is observed in columns.


Block
Elements are organised into blocks by the orbital type in which the outer electrons are found. These blocks are named for the characteristic spectra they produce: sharp, principal, diffuse, and fundamental.


Atomic Number
The number of protons in the nucleus.


Atomic Radius/non -bonded (Å)
based on Van der Waals forces (where several isotopes exist, a value is presented for the most prevalent isotope). These values were calculated using a multitude of methods including crystallographic data, gas kinetic collision cross sections, critical densities, liquid state properties, for more details please refer to the CRC Handbook of Chemistry and Physics.


Electron Configuration
The arrangements of electrons above the last (closed shell) noble gas.


Isotopes
Elements are defined by the number of protons in its centre (nucleus), whilst the number of neutrons present can vary. The variations in the number of neutrons will create elements of different mass which are known as isotopes.


Melting Point (oC)
The temperature at which the solid-liquid phase change occurs.


Melting Point (K)
The temperature at which the solid-liquid phase change occurs.


Melting Point (oF)
The temperature at which the solid-liquid phase change occurs.


Boiling Point (oC)
The temperature at which the liquid-gas phase change occurs.


Boiling Point (K)
The temperature at which the liquid-gas phase change occurs.


Boiling Point (oF)
The temperature at which the liquid-gas phase change occurs.


Sublimation
Elements that do not possess a liquid phase at atmospheric pressure (1 atm) are described as going through a sublimation process.


Density (g cm-3)
Density is the mass of a substance that would fill 1 cm3 at room temperature.


Relative Atomic Mass
The mass of an atom relative to that of Carbon-12. This is approximately the sum of the number of protons and neutrons in the nucleus. Where more than one isotope exists the value given is the abundance weighted average.


Key Isotopes (% abundance)
An element must by definition have a fixed number of protons in its nucleus, and as such has a fixed atomic number, however variants of an element can exist with differing numbers of neutrons, and hence a different atomic masses (e.g. 12C has 6 protons and 6 neutrons and 13C has 6 protons and 7 neutrons).


CAS number
The Chemical Abstracts Service registry number is a unique identifier of a particular chemical, designed to prevent confusion arising from different languages and naming systems (where several isotopes exist, a value is presented for the most prevalent isotope).

Fact box

 
Group 17  Melting point -101.5 oC, -150.7 oF, 171.65 K 
Period Boiling point -34.04 oC, -29.272 oF, 239.11 K 
Block Density (g cm-3) 0.002898 
Atomic number 17  Relative atomic mass 35.453  
State at room temperature Gas  Key isotopes 35Cl, 37Cl 
Electron configuration [Ne] 3s23p5  CAS number 7782-50-5 
ChemSpider ID 4514529 ChemSpider is a free chemical structure database
 

Uses and properties terminology


Image Explanation

Murray Robertson is the artist behind the images which make up Visual Elements. This is where the artist explains his interpretation of the element and the science behind the picture.


Natural Abundance

Where this element is most commonly found in nature.


Biological Roles

The elements role within the body of humans, animals and plants. Also functionality in medical advancements both today and years ago.


Appearance

The description of the element in its natural form.

Uses and properties

 
Image explanation

The symbol shows a gas mask. This is because chlorine is a toxic gas, and has been used as a chemical weapon. Chlorine is yellowy-green in colour, as is the image.

Appearance

A yellowy-green dense gas with a choking smell.

Uses

Chlorine kills bacteria – it is a disinfectant. It is used to treat drinking water and swimming pool water. It is also used to make hundreds of consumer products from paper to paints, and from textiles to insecticides.

About 20% of chlorine produced is used to make PVC. This is a very versatile plastic used in window frames, car interiors, electrical wiring insulation, water pipes, blood bags and vinyl flooring.

Another major use for chlorine is in organic chemistry. It is used as an oxidising agent and in substitution reactions. 85% of pharmaceuticals use chlorine or its compounds at some stage in their manufacture.

In the past chlorine was commonly used to make chloroform (an anaesthetic) and carbon tetrachloride (a dry-cleaning solvent). However, both of these chemicals are now strictly controlled as they can cause liver damage.

Chlorine gas is itself very poisonous, and was used as a chemical weapon during the First World War.

Biological role

The chloride ion is essential to life. It is mostly present in cell fluid as a negative ion to balance the positive (mainly potassium) ions. It is also present in extra-cellular fluid (eg blood) to balance the positive (mainly sodium) ions.

We get most of the chloride we need from salt. Typical daily salt intake is about 6 grams, but we could manage with half this amount.

Natural abundance

Chlorine is not found uncombined in nature. Halite (sodium chloride or ‘common salt’) is the main mineral that is mined for chlorine. Sodium chloride is a very soluble salt that has been leached into the oceans over the lifetime of the Earth. Several salt beds, or ‘lakes’ are found where ancient seas have evaporated, and these can be mined for chloride.

Chlorine is also found in the minerals carnallite (magnesium potassium chloride) and sylvite (potassium chloride).

40 million tonnes of chlorine gas are made each year from the electrolysis of brine (sodium chloride solution). This process also produces useful sodium hydroxide.

 
Atomic data terminology

Atomic radius/non -bonded (Å)
Based on Van der Waals forces (where several isotopes exist, a value is presented for the most prevalent isotope). These values were calculated using a multitude of methods including crystallographic data, gas kinetic collision cross sections, critical densities, liquid state properties,for more details please refer to the CRC Handbook of Chemistry and Physics.


Electron affinity (kJ mol-1)
The energy released when an additional electron is attached to the neutral atom and a negative ion is formed (where several isotopes exist, a value is presented for the most prevalent isotope). *


Electronegativity (Pauling scale)
The degree to which an atom attracts electrons towards itself, expressed on a relative scale as a function bond dissociation energies, Ed in eV. χA - χB =(eV)-1/2sqrt(Ed(AB)-[Ed(AA)+Ed(BB)]/2), with χH set as 2.2 (where several isotopes exist, a value is presented for the most prevalent isotope).


1st Ionisation energy (kJ mol-1)
The minimum energy required to remove an electron from a neutral atom in its ground state (where several isotopes exist, a value is presented for the most prevalent isotope).


Covalent radius (Å)
The size of the atom within a covalent bond, given for typical oxidation number and coordination (where several isotopes exist, a value is presented for the most prevalent isotope). ***

Atomic data

 
Atomic radius, non-bonded (Å) 1.75 Covalent radius (Å) 1
Electron affinity (kJ mol-1) 348.602 Electronegativity
(Pauling scale)
3.16
Ionisation energies
(kJ mol-1)
 
1st
1251.185
2nd
2297.661
3rd
3821.781
4th
5158.604
5th
6541.700
6th
9361.965
7th
11018.211
8th
33603.885
 
Bond enthalpies terminology

Covalent Bonds
The strengths of several common covalent bonds.

Bond enthalpies

 
Covalent bonds
Cl–Cl  243.4  kJ mol -1 Cl–H  432  kJ mol -1 C–Cl  346  kJ mol -1
C–Cl  327  kJ mol -1  
 

Mining/Sourcing Information

Data for this section of the data page has been provided by the British Geological Survey. To review the full report please click here or please look at their website here.


Key for numbers generated


Governance indicators

1 (low) = 0 to 2

2 (medium-low) = 3 to 4

3 (medium) = 5 to 6

4 (medium-high) = 7 to 8

5 (high) = 9


Reserve distribution (%)

1 (low) = 0 to 30 %

2 (medium-low) = 30 to 45 %

3 (medium) = 45 to 60 %

4 (medium-high) = 60 to 75 %

5 (high) = 75 %

(Where data are unavailable an arbitrary score of 2 was allocated. For example, Be, As, Na, S, In, Cl, Ca and Ge are allocated a score of 2 since reserve base information is unavailable. Reserve base data are also unavailable for coal; however, reserve data for 2008 are available from the Energy Information Administration (EIA).)


Production Concentration

1 (low) = 0 to 30 %

2 (medium-low) = 30 to 45 %

3 (medium) = 45 to 60 %

4 (medium-high) = 60 to 75 %

5 (high) = 75 %


Crustal Abundance

1 (low) = 100 to 1000 ppm

2 (medium-low) =10 to 100 ppm

3 (medium) = 1 to 10 ppm

4 (medium-high) = 0.1 to 1 ppm

5 (high) = 0.1 ppm

(Where data are unavailable an arbitrary score of 2 was allocated. For example, He is allocated a score of 2 since crustal abundance data is unavailable.)


Explanations for terminology


Crustal Abundance (ppm)

The abundance of an element in the Earth's crust in parts-per-million (ppm) i.e. The number of atoms of this element per 1 million atoms of crust.


Sourced

The country with the largest reserve base.


Reserve distribution (%)

This is a measure of the spread of future supplies, recording the percentage of a known resource likely to be available in the intermediate future (reserve base) located in the top three countries.


Production Concentrations

This reports the percentage of an element produced in the top three countries. The higher the value, the larger risk there is to supply.


Political stability of top producer

The World Bank produces a global percentile rank of political stability. The scoring system is given below, and the values for all three production countries were summed.


Relative Supply Risk Index

The Crustal Abundance, Reserve distribution (%), Production Concentration and Governance Factor scores are summed and then divided by 2, to provide an overall Relative Supply Risk Index.

Supply risk

 
Relative supply risk 4
Crustal abundance (ppm) 145
Recycling rate (%) Unknown
Substitutability Unknown
Production concentration (%) 24.3
Reserve distribution (%) n/a
Top 3 producers
  • 1) China
  • 2) India
  • 3) USA
Top 3 reserve holders
  • 1) n/a
Political stability of top producer 8
Political stability of top reserve holder Unknown
 

Oxidation states and isotopes


Key for Isotopes


Half Life
  y years
  d days
  h hours
  m minutes
  s seconds
Mode of decay
  α alpha particle emission
  β negative beta (electron) emission
  β+ positron emission
  EC orbital electron capture
  sf spontaneous fission
  ββ double beta emission
  ECEC double orbital electron capture

Terminology


Common Oxidation states
The oxidation state of an atom is a measure of the degree of oxidation of an atom. It is defined as being the charge that an atom would have if all bonds were ionic. Free atoms have an oxidation state of 0, and the sum of oxidation numbers within a substance must equal the overall charge.


Important Oxidation states
The most common oxidation states of an element in its compounds.


Isotopes
Elements are defined by the number of protons in its centre (nucleus), whilst the number of neutrons present can vary. The variations in the number of neutrons will create elements of different mass which are known as isotopes.

Oxidation states and isotopes

 
Common oxidation states 7, 5, 3, 1, -1
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  35Cl 34.969 75.76
  37Cl 36.966 24.24
 

Pressure and temperature - advanced terminology


Specific heat capacity (J kg-1 K-1)

Specific heat capacity is the amount of energy needed to change the temperature of a kilogram of a substance by 1 K.


Young's modulus (GPa)

Young's modulus is a measure of the stiffness of a substance, that is, it provides a measure of how difficult it is to extend a material, with a value given by the ratio of tensile strength to tensile strain.


Shear modulus (GPa)

The shear modulus of a material is a measure of how difficult it is to deform a material, and is given by the ratio of the shear stress to the shear strain.


Bulk modulus (GPa)

The bulk modulus is a measure of how difficult to compress a substance. Given by the ratio of the pressure on a body to the fractional decrease in volume.


Vapour Pressure (Pa)

Vapour pressure is the measure of the propensity of a substance to evaporate. It is defined as the equilibrium pressure exerted by the gas produced above a substance in a closed system.

Pressure and temperature data – advanced

 
Specific heat capacity
(J kg-1 K-1)
479 Young's modulus (GPa) Unknown
Shear modulus (GPa) Unknown Bulk modulus (GPa) 1.1 (liquid)
Vapour pressure  
Temperature (K)
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
Pressure (Pa)
- - - - - - - - - - -
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History

Hydrochloric acid (HCl) was known to the alchemists. The gaseous element itself was first produced in 1774 by Carl Wilhelm Scheele at Uppsala, Sweden, by heating hydrochloric acid with the mineral pyrolusite which is naturally occuring manganese dioxide, MnO2. A dense, greenish-yellow gas was evolved which he recorded as having a choking smell and which dissolved in water to give an acid solution. He noted that it bleached litmus paper, and decolourised leaves and flowers.


Humphry Davy investigated it in 1807 and eventually concluded not only that it was a simple substance, but that it was truly an element. He announced this in 1810 and yet it took another ten years for some chemists finally to accept that chlorine really was an element.

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Podcasts

Listen to Chlorine Podcast
Transcript :

Chemistry in its element - Chlorine


(Promo) 

You're listening to Chemistry in its element brought to you by Chemistry World, the magazine of the Royal Society of Chemistry.

(End promo)


Chris Smith

Hello. What's got three isotopes, keeps swimming pools clean, damages the ozone layer and is used in more chemical synthesis reactions than you can shake a benzene ring at. Well the man with the answer is Tim Harrison.


Tim Harrison 

Chlorine is what you might describe as a Jekyll and Hyde element; it is the friend of the synthetic chemist and has found a use in a number of 'nice' applications such as the disinfecting of drinking water and keeping our swimming pools clean. It also has an unpleasant side, being the first chemical warfare agent and taking some of the blame in the depletion of the Earth's ozone layer. 

Elemental chlorine is a pale, yellowy green gas at room temperature. It was the Greek word khlôros meaning 'yellowish-green' that was used as inspiration by Sir Humphrey Davy when he named this element in the 19th century. 

This element was first isolated in 1774 by the Swiss-German chemist Carl Wilhelm Scheele, by reacting hydrochloric acid with manganese (IV) oxide. But he failed to realise his achievement, mistakenly believing it also contained oxygen. It was Davy in 1810 who finally concluded that Scheele had made elemental chlorine. 

Chlorine is in group 17 of periodic table, also called the halogens, and is not found as the element in nature - only as a compound. The most common of these being salt, or sodium chloride, and the potassium compounds sylvite (or potassium chloride) and carnallite (potassium magnesium chloride hexahydrate). It is also estimated that there are around two thousand organic chlorine compounds. 

Chlorine has two stable isotopes chlorine-35 and chlorine-37with Chlorine-35 accounting for roughly 3 out of every 4 naturally occurring chlorine atoms. Chlorine-36 is also known naturally and is a radioactive isotope with a half life of about 30,000 years. 

Chlorine has a major role to play in synthetic organic chemistry, taking part in three of the most common reaction mechanisms. In the first of these, the photochemical substitution reaction, chlorine reacts with an alkane by replacing one of the hydrogen atoms attached to a carbon forming a chloroalkane. This radical reaction is initiated by the use of sunlight or ultraviolet light to split diatomic chlorine into two radicals. 

Chlorine can also react with alkenes via the electrophilic addition mechanism. This time two chlorine atoms add to a molecule across the electron-rich carbon-carbon double bond. This reaction has to be carried out in the dark to avoid complications with competing free radical substitutions. 

A third common mechanism is electrophilic substitution, which occurs when chlorine reacts with a benzene ring by replacing a hydrogen atom forming chlorobenzene and hydrogen chloride. This reaction is most commonly known as the Friedal-Crafts reaction. 

Chlorine also has a multitude of industrial uses. Including making bulk materials like bleached paper products, plastics such as PVC and the solvents tetrachloromethane, chloroform and dichloromethane. It is also used to make dyes, textiles, medicines, antiseptics, insecticides and paints. 

It's best known uses however are probably in making bleaches such as 'Domestos' and in treating drinking and swimming pool waters to make them safe to use and of course its role as a chemical warfare agent. 

The treatment of water with chlorine began in London after a cholera outbreak in 1850 when the physician and pioneering hygienist John Snow identified a well in Soho as the source of the outbreak. Chlorine is still used in most sewage treatment works today. 

Snow also used a compound of chlorine - chloroform with the formula CHCl3 - as an anesthetic to aid the childbirth of two of Queen Victoria's children.

 The use of chlorine gas as a chemical weapon was pioneered by German chemist Fritz Haber, who is better known for his work with ammonia. It was first used against the Allied soldiers in the battle of Ypres during the first world war. While it was quickly replaced by the more deadly phosgene and mustard gases, chlorine gas has been used as a weapon as recently as 2007 in Iraq during the second gulf war. 

Chlorine was also once used to make a series of aerosol solvents and refrigerants called chlorofluorocarbons or CFCs. However their use was stopped once it became apparent that when in the atmosphere these compounds absorb ultraviolet light and cause homolytic bond fission producing a chlorine free radical which in turn reacts with ozone. 

This has led to a reduction in the concentration of ozone in the so-called ozone layer, and therefore a reduction in the protection for those of us on the surface of the planet making us more susceptible to skin cancers. So, that's chlorine - a Jeckll and Hyde element with an extremely wide range of applications. 


Chris Smith 

So slap on your sun screen. Tim Harrison was telling the tale of Element number 17, and that's chlorine. Tim's based at the University of Bristol's ChemLabs. Next week, the stuff that gives itself an x-ray. 


Brian Clegg 

This grey metallic element gives off beta particles as it decays. These can cause radioactive damage in their own right, but prometheum is probably most dangerous because those beta particles generate X-rays when they hit heavy nuclei, making a sample of promethium bathe its surroundings in a constant low dosage x-ray beam. It was initially used to replace radium in luminous dials. Promethium chloride was mixed with phosphors that glow yellowy-green or blue when radiation hits them. However, as the dangers of the element's radioactive properties became apparent, this too was dropped from the domestic glow-in-the-dark market, only employed now in specialist applications. 


Chris Smith 

And you can hear what some of those applications are when Brian Clegg looks at the story of promethium in next week's Chemistry in its Element. In the meantime more elements are available from the Chemistry in its Element Podcast, that's on iTunes or on the web at chemistryworld.org/elements. I'm Chris Smith, thank you very much for listening and goodbye. 


(Promo) 

Chemistry in its element is brought to you by the Royal Society of Chemistry and produced by thenakedscientists.com. There's more information and other episodes of Chemistry in its element on our website at chemistryworld.org/elements.

(End promo) 

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  Help Text

Resources

Description :
The Group 7 elements are called the halogens. This experiment involves some reactions of the halogens.
Description :
More reactions of chlorine
Description :
Studying the physical characteristics of the group 7 non-metals known as the halogens
Description :
How does the reaction compare with other halogens?
Description :
Each of the halogens forms a monovalent (singly-charged) anion. In this experiment you will be looking at the similarities and differences in some of the properties of these halide ions.
Description :
Demonstrating how the more reactive fluorine displaces the less reactive halogens
 

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References

 
Images:  Visual Elements © Murray Robertson 2011
Mining and Sourcing data:  British Geological Survey – natural environment research council.
Text:  John Emsley Nature’s Building Blocks: An A-Z Guide to the Elements, Oxford University Press, 2nd Edition, 2011.
Additional information for platinum, gold, neodymium and dysprosium obtained from Material Value Consultancy Ltd www.matvalue.com
Data: CRC Handbook of Chemistry and Physics, CRC Press, 92nd Edition, 2011.
G. W. C. Kaye and T. H. Laby Tables of Physical and Chemical Constants, Longman, 16th Edition, 1995.
Members of the RSC can access these books through our library.