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 18  Melting point -189.36 oC, -308.848 oF, 83.79 K 
Period Boiling point -185.85 oC, -302.53 oF, 87.3 K 
Block Density (kg m-3) 1656 (40 K) 
Atomic number 18  Relative atomic mass 39.948  
State at room temperature Gas  Key isotopes 40Ar 
Electron configuration [Ne] 3s23p6  CAS number 7440-37-1 
ChemSpider ID 22407 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 reflects the use of the element in the welding industry. Argon provides an inert atmosphere in which welded metals will not oxidise.

Appearance

Argon is a colourless, odourless gas that is totally inert to other substances.

Source

Uses

Argon is obtained commercially from liquid air. It is used in electric light bulbs and fluorescent tubes at a pressure of about 3 mm. Industrially it is used as an inert gas shield for arc welding, and as a blanket for the production of titanium and other reactive elements.

Biological role
Argon has no known biological role.
Natural abundance

The third most abundant atmospheric gas, making up 0.94% of the Earth’s atmosphere. The quantity has increased since the Earth was formed because radioactive potassium turns into argon as it decays.

 
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) 1.880 Covalent radius (Å) 1.01
Electron affinity (kJ mol-1) Not stable Electronegativity
(Pauling scale)
Unknown
Ionisation energies
(kJ mol-1)
 
1st
1520.571
2nd
2665.855
3rd
3930.809
4th
5770.783
5th
7238.324
6th
8781.027
7th
11995.337
8th
13841.775
 

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 Unknown
Country with largest reserve base Unknown
Crustal abundance (ppm) Unknown
Leading producer Unknown
Reserve base distribution (%) Unknown
Production concentration (%) Unknown
Total governance factor(production) Unknown
Top 3 countries (mined)
  • Unknown
Top 3 countries (production)
  • Unknown
 

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 Unknown
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  36Ar 35.968 0.336
  38Ar 37.963 0.063
  40Ar 39.962 99.6
 

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)
20.786 Young's modulus (GPa) Unknown
Shear modulus (GPa) Unknown Bulk modulus (GPa) Unknown
Vapour pressure  
Temperature (K)
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
Pressure (Pa)
- - - - - - - - - - -
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History

Although argon is abundant in the Earth’s atmosphere, it evaded discovery until 1894 when Lord Rayleigh and William Ramsay first separated it from liquid air. In fact the gas had been isolated in 1785 by Henry Cavendish who had noted that about 1% of air would not react even under the most extreme conditions. That 1% was argon.


Argon was discovered as a result of trying to explain why the density of nitrogen extracted from air differed from that obtained by the decomposition of ammonia. 


Ramsay removed all the nitrogen from the gas he had extracted from air, and did this by reacting it with hot magnesium, forming the solid magnesium nitride. He was then left with a gas that would not react and when he examined its spectrum he saw new groups of red and green lines, confirming that it was a new element.

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Podcasts

Listen to Argon Podcast
Transcript :

Chemistry in Its Element - Argon


 

 (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 the element that's so indolent that scientists at one time thought it wouldn't react with anything, but in the chemical world laziness can have its advantages especially if it's super quiet car tyres or a safe chemical with which to pump up your diving suit that you're after.  

Here's John Emsley.

John Emsley

It's lazy, it's hard-working, it's colourless, it's colourful - it's argon!

Argon's name comes from the Greek word argos meaning lazy and indeed for more than a hundred years after its discovery chemists were unable to get it to combine with any other elements. But in the year 2000, chemists at the University of Helsinki led by Markku Räsänen announced the first ever compound: argon fluorohydride. They made it by condensing a mixture of argon and hydrogen fluoride on to caesium iodide at -265oC and exposing it to UV light. On warming above just -246oC it reverted right back to Argon   and hydrogen fluoride. And no other process has ever induced argon to react - [a truly lazy element]. 

There are 50 trillion tonnes of argon swirling around in the Earth's atmosphere and this has slowly built-up over billions of years, almost all coming from the decay of the radioactive isotope potassium-40 which has a half-life of 12.7 billion years. Although argon makes up 0.93% of the atmosphere it evaded discovery until 1894 when the physicist Lord Rayleigh and the chemist William Ramsay identified it. In 1904 Rayleigh won the Nobel Prize for Physics and Ramsay won the Nobel Prize for Chemistry for their work. 

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, with which nitrogen reacts to form magnesium nitride. 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. Although in fact it contained traces of the other noble gases as well.

Argon was first isolated in 1785 in Clapham, South London, by Henry Cavendish. He had passed electric sparks through air and absorbed the gases which formed, but he was puzzled that there remained an unreactive 1%. He didn't realise that he had stumbled on a new gaseous element. 

Most argon goes to making steel where it is blown through the molten iron, along with oxygen. Argon does the stirring while the oxygen removes carbon as carbon dioxide. It is also used when air must be excluded to prevent oxidation of hot metals, as in welding aluminium and the production of titanium to exclude air. Welding aluminium is done with an electric arc which requires a flow of argon of at 10-20 litres per minute. Atomic energy fuel elements are protected with an argon atmosphere during refining and reprocessing.

The ultra-fine metal powders needed to make alloys are produced by directing a jet of liquid argon at a jet of the molten metal. 

Some smelters prevent toxic metal dusts from escaping to the environment by venting them through an argon plasma torch. In this, argon atoms are electrically charged to reach temperatures of 10 000 °C and the toxic dust particles passing through it are turned into to a blob of molten scrap.

For a gas that is chemically lazy argon has proved to be eminently employable. Illuminated signs glow blue if they contain argon and bright blue if a little mercury vapour is also present. Double glazing is even more efficient if the gap between the two panes of glass is filled with argon rather than just air because argon is a poorer conductor of heat. Thermal conductivity of argon at room temperature (300 K) is 17.72 mW m-1K-1  (milliWatts per metre per degree) whereas for air it is 26 mW m-1K-1.For the same reason argon is used to inflate diving suits. Old documents and other things that are susceptible to oxidation can be protected by being stored in an atmosphere of argon. Blue argon lasers are used in surgery to weld arteries, destroy tumors and correct eye defects.

The most exotic use of argon is in the tyres of luxury cars. Not only does it protect the rubber from attack by oxygen, but it ensures less tyre noise when the car is moving at speed.   Laziness can prove useful in the case of this element.   Its high tech uses range from double glazing and laser eye surgery to putting your name in lights.

 

Chris Smith

John Emsley unlocking the secrets of the heavier than air noble gas Argon.   Next week, would you marry this man?  

 

 

Steve Mylon

It's almost never the case where the popular elements are that way because of their utility and interesting chemistry.   But for Gold and Silver it's all so superficial. They are more popular because they're prettier. My wife for example, a non chemist, wouldn't dream of wearing a copper wedding ring. That might have something to do with the fact that copper oxide has an annoying habit of dyeing your skin green. But if she only took the time to learn about copper, to get to know it some; maybe then she would be likely to turn her back on the others and wear it with pride. 

 

Chris Smith

Steve Mylon's back to cross your palm with copper 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 :
The activity sets some critical thinking and pattern spotting tasks in the context of the noble gases. The students are given data that can be manipulated to show a directly proportional relationship,...
Description :
Estimate the percentage of ‘empty space’ in a sample of gaseous argon.
Description :
A teaching resource on Group 8 (18) - The Noble Gases, supported by video clips from the Royal Institution Christmas Lectures® 2012.
Description :
Explore chemistry & industrial processes with 15 tutorials, all available on the Alchemy website.
Description :
An introduction to extracting gases from air
Description :
A series of short experiments and demonstrations about the chemistry of light, taken from a lecture by Peter Wothers from the University of Cambridge
 

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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.