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/Interesting 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 (kgm-3)
Density is the weight of a substance that would fill 1 m3 (at 298 K unless otherwise stated).


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 (kg m-3) 2030 (113 K) 
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
 

Interesting Facts 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 / Interesting Facts

 
Image explanation

The symbol is a version of a generic hazard warning associated with the toxic nature of the gas.

Appearance

A yellowy-green dense gas with a choking smell.

Source

Uses

Chlorine gas is made on a large scale from salt (sodium chloride). It is used to sterilise drinking water, to disinfect swimming pools and in the manufacture of many consumer products such as paper, dyestuffs, textiles, petroleum products, medicines, antiseptics, insecticides, foodstuffs, solvents, paints and plastics, especially PVC. It is also used to produce bleaches, chlorates, chloroform, carbon tetrachloride and bromine. A further substantial use for this element is in organic chemistry, both as an oxidising agent and in substitution reactions. As the free element it is 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, and in extra-cellular fluid (eg blood) to balance the (mainly sodium) ions. Our daily intake is about 6 grams, mainly as salt, but we could manage with half this amount.

Natural abundance

Chlorine is not found uncombined in nature but chiefly as sodium chloride (common salt). This very soluble salt has been leached into the oceans over the lifetime of the planet, but several salt beds, or ‘lakes’ are found where ancient seas have evaporated. Chlorine is also found in the minerals carnallite and sylvite.

 
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) 1.750 Covalent radius (Å) 1
Electron affinity (kJ mol-1) 348.602 Electronegativity
(Pauling scale)
3.160
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
 
Bonding and Enthalpies terminology

Covalent Bonds
The strengths of several common covalent bonds.

Bonding / Enthalpies

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


Total Governance Factor

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 Base Distribution, Production Concentration and Governance Factor scores are summed and then divided by 2, to provide an overall Relative Supply Risk Index.

Supply Risk

 
Scarcity factor 4.0
Country with largest reserve base n/a
Crustal abundance (ppm) 145
Leading producer China
Reserve base distribution (%) n/a
Production concentration (%) 24.30
Total governance factor(production) 8
Top 3 countries (mined)
  • 1) n/a
Top 3 countries (production)
  • 1) China
  • 2) India
  • 3) USA
 

Oxidation states/ 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 / 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


Molar Heat Capacity (J mol-1 K-1)

Molar heat capacity is the energy required to heat a mole 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 / Temperature - Advanced

 
Molar heat capacity
(J mol-1 K-1)
33.949 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 - Sulfur


  (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, this week stinky sediments, skunks and the smell of hell.   Well they all begin with the letter S, and so does this week's element.   Here's Steve Mylon.

 

Steve Mylon

 

"How did it smell?" That was the only question I needed to ask a geologist colleague of mine about the sediment she was trying to understand.   The smell of the sediment tells a great deal about the underlying chemistry.   Thick black anoxic sediments can be accompanied by a putrid smell which is unique to reduced sulfur.  

 

Maybe this is why sulfur has such a bad reputation. My son wouldn't eat eggs for 6 months when he got a smell of his first rotten one.   In the bible it seems that whenever something bad happens or is about to happen burning sulfur is in the picture:

For example,

In Genesis we hear, "the lord rained down burning sulfur on Sodom and Gomorrah"

 

And in Revelation we read that the sinners will find their place in a fiery lake of burning sulfur."  

 

The odd thing is that in both cases we shouldn't expect anything smelly to be produced.   When sulfur burns in air, it generally forms sulfur dioxide or sulfur trioxide both of which lack any smell.   These compounds can further oxidize and rain out as sulfuric or sulfurous acid.   This is the mechanism for acid rain which has reeked havoc on the forests of the northeastern United States as sulfur rich coals are burned to generate electricity in midwestern states and carried east by prevailing winds where sulfuric acid is rained out causing all sorts of ecological problems.  

 

Additionally, the combination of burning coal and fog creates smog in many industrial cities causing respiratory problems among the locals.   Here too, sulfur dioxide and sulfuric acid are implicated as the culprits.   But again, there is no smell associated with this form of sulfur.

 

So if hell or the devil is said have the 'smell of sulfur', maybe that's not so bad. 

 

But reduce sulfur by giving it a couple of electrons, and its smell is unmistakable.   The requirement of sulfur reduction to sulfide has clearly been lost in translation .  

 

Hell that smells like hydrogen sulfide or any number of organic-sulfur compound will not be a nice place at all.   The organic sulfide compounds known as thiols or mercaptans smell so bad, that they are commonly added to odorless natural gas in very small quantities in order to serve as a 'smell alarm' should there be leak in a natural gas line.   Skunks take advantage of the foul smell of butyl seleno-mercaptan as a means of defending themselves against their enemies.   And for me, personally, the worst chemistry of all occurs when reduced sulfur imparts a bad (skunky) taste in bottles of wine or beer. -bound to ruin a nice night out on the town or an afternoon at the local pub.

 

So, where does the "smell of hell" come from in anoxic sediments.   Interestingly, some bacteria have evolved to make use of oxidized sulfur , sulfate, as an electron acceptor during respiration.   In a similar manner to the way humans reduce elemental oxygen to water, these bacteria reduce sulfate to hydrogen sulfide- They clearly don't mind the smell.  

 

Smell is not the only interesting chemistry that accompanies reduced sulfur.   The deep black associated with anoxic sediments results from the low solubility of most metal sulfides.   Sulfate reduction to sulfide generally accompanies the precipitation of pyrite (iron sulfide), cinnabar (mercury sulfide), galena (lead sulfide) and many more minerals.   These metal sulfides have become an important industrial source for many of these important metals.

 

Industry is one place you are almost certain to find sulfur or more importantly sulfuric acid which is used in processes ranging from fertilizer production to oil refining. In fact sulfuric acid ranks as the most highly produced chemical in the industrialized world.   Imagine that, the element with such a hellish reputation has become one of the most important.  

 

And some even suggest that sulfur could save the planet.     The biogenic compound dimethylsulfide (DMS) is produced from the cleavage of dimethylsufonoprioponate, an osmotic regulatory compound produced by plankton in the ocean.   The volatility and low solubility of DMS results in some 20 Tg (10^12) of sulfur emitted to the atmosphere annually. DMS is oxidized to SO2 and finally to sulfuric acid particles which can act as cloud condensation nuclei forming clouds which have a net cooling effect to the planet. 

 

  Imagine warmer temperatures followed by greater biological activity resulting in more DMS to the atmosphere.   The resulting cloud formation might work to cool a warming planet.   It's almost like the plankton are opening an umbrella made up-in part- of sulfur.   From a symbol of damnation to savior...what a turn around!!. 

 

Chris Smith

 

Steve Mylon sniffing out the stinky story of Sulfur.   Thankfully next week's element is a lot less odiforous.  

 

John Emsley

 

The story of its discovery started when Rayleigh found that the nitrogen extracted from the air had a higher density than that made by decomposing ammonia. The difference was small but real. Ramsay wrote to Rayleigh suggesting that he should look for a heavier gas in the nitrogen got from air, while Rayleigh should look for a lighter gas in that from ammonia. Ramsay removed all the nitrogen from his sample by repeatedly passing it over heated magnesium.   He was left with one percent which would not react and found it was denser than nitrogen. Its atomic spectrum showed new red and green lines, confirming it a new element. 

 

Chris Smith

 

And that new element was Argon nicknamed the lazy element because originally scientists thought that it wouldn't react with anything.   Now we know that's not true and John Emsley will be here to unlock Argon secrets on next week's Chemistry in its Element, I hope you can join us.   I'm Chris Smith, thank you for listening and goodbye.

 

(Promo)

 

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

 

(End promo)

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  Help Text

Resources

Description :
How does reactivity change upon descending the group?
Description :
The Group 7 elements are called the halogens. This experiment involves some reactions of the halogens.
Description :
This activity compares the colours of three halogens in aqueous solution and in a non-polar solvent. These halogens also react to a small extent with water, forming acidic solutions with bleaching pr...
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?
 

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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.