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 -111.74 oC, -169.132 oF, 161.41 K 
Period Boiling point -108.099 oC, -162.578 oF, 165.051 K 
Block Density (kg m-3) 3560 (88 K) 
Atomic number 54  Relative atomic mass 131.29  
State at room temperature Gas  Key isotopes 132Xe 
Electron configuration [Kr] 4d105s25p6  CAS number 7440-63-3 
ChemSpider ID 22427 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
Electro flash. The icon used here reflects the use of the gas in camera flash technology, usually a tube filled with xenon gas, with electrodes on either end and a metal trigger plate at the middle of the tube.
Appearance
A colourless, odourless gas that makes up 0.086 parts per million of the atmosphere. About half a tonne a year is produced from liquid air and used for research purposes.
Uses
Xenon is little used outside research. However, it is used in certain specialised light sources which require an instant, intense light such as the high-speed electronic flash bulbs used by photographers. The high volatility of this element’s electron structure produces this type of light. Xenon in a vacuum tube produces a beautiful blue glow when excited by an electrical discharge, and finds application in electron tubes, stroboscopic lights and bactericidal lamps.
Biological role
Xenon has no known biological role. It is not itself toxic, but its compounds are highly toxic because of their strong oxidising characteristics.
Natural abundance
Xenon is present in the atmosphere at a concentration of 0.086 parts per million by volume. It can be found in the gases which evolve from certain mineral springs. Commercially it is obtained by extraction from liquid air.
 
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) 2.160 Covalent radius (Å) 1.36
Electron affinity (kJ mol-1) Not stable Electronegativity
(Pauling scale)
2.600
Ionisation energies
(kJ mol-1)
 
1st
1170.347
2nd
2023.778
3rd
3099.396
4th
-
5th
-
6th
-
7th
-
8th
-
 

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 6, 4, 2
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  124Xe 123.906 0.095 > 1017 β-β- 
  126Xe 125.904 0.089
  128Xe 127.904 1.91
  129Xe 128.905 26.401
  130Xe 129.904 4.071
  131Xe 130.905 21.232
  132Xe 131.904 26.909
  134Xe 133.905 10.436 > 1.1 x 1016 β-β- 
  136Xe 135.907 8.857 > 8.5 x 1021 β-β- 
 

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

Xenon was discovered in July 1898 by William Ramsay and Morris Travers at University College London. They had already extracted neon, argon, and krypton from liquid air, and wondered if it contained other gases. The wealthy industrialist Ludwig Mond gave them a new liquid-air machine and they used it to extract more of the rare gas krypton. By repeatedly distilling this, they eventually isolated a heavier gas, and when they examined this in a vacuum tube it gave a beautiful blue glow. They realised it was yet another member of the ‘inert’ group of gaseous elements as they were then known because of their lack of chemical reactivity. They called the new gas xenon. It was this gas which Neil Bartlett eventually showed was not inert by making a fluorine derivative in 1962. So far more than 100 xenon compounds have been made.

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Podcasts

Listen to Xenon Podcast
Transcript :

Chemistry in its element - xenon


(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) 

Meera Senthilingam 

This week we enter the stranger realms of chemistry as we hear the story of xenon. He's Peter Wothers.

Peter Wothers

When William Ramsay named his newly-discovered element after the Greek Xenon for stranger, I'm sure he had no idea just how strange and important this element would turn out to be.   He could never have foreseen that his discovery would one day be used to light our roads at night, image the workings of a living lung, or propel spaceships.

The story of xenon begins in 1894 when Lord Rayleigh and William Ramsay were investigating why nitrogen extracted from chemical compounds is about one-half per cent lighter than nitrogen extracted from the air - an observation first made by Henry Cavendish 100 years earlier. Ramsay found that after atmospheric nitrogen has reacted with hot magnesium metal, a tiny proportion of a heavier and even less reactive gas is left over.   They named this gas argon from the Greek for lazy or inactive to reflect its extreme inertness.   The problem was, where did this new element fit into Mendeleev's periodic table of the elements?   There were no other known elements that it resembled, which led them to suspect that there was a whole family of elements yet to be discovered.   Remarkably, this turned out to be the case.  

The following year, Ramsay confirmed the presence in certain radioactive rocks of the lightest member of the group, helium, trapped as it was formed during the alpha-particle emission from elements such as uranium.     In 1897 Ramsay boldly stated that 'there should be an undiscovered element between helium and argon, with an atomic weight of 20.   Pushing this analogy further, it is to be expected that this element should be as indifferent to union with other elements, as the two allied elements.'

Initially, Ramsay looked for the new element in rock samples, but around this time, a new breakthrough in science began to emerge - the production and manipulation of liquid air.   In May 1898, Ramsay instructed his student Morris Travers to allow a sample of liquid air to evaporate until just a few millilitres remained.   This he did, and upon examining the electrical discharge of the residue with a spectroscope, the appearance of a bright yellow line and a brilliant green line confirmed the presence of a new element.   But it wasn't the missing element with mass 20 they had been searching for, it was actually about twice as heavy as argon and is the element beneath argon in the periodic table.   They called it krypton, from the Greek for hidden.

Realising that their missing lighter element should actually have a lower boiling point than argon, they looked again at some of the more volatile fractions of gas from liquefied atmospheric residues.

On Sunday, June 12, 1898 they prepared a sample for examination with the spectroscope, but as they turned on the current through the gas, they had no need for the prism to split the light, for the brilliant red glow of the tube confirmed the presence of the new missing element they named neon.

In an attempt to isolate more of the krypton, Ramsay and Travers repeatedly distilled out the heavier fractions of the liquefied gases.   Travers writes: 'one evening late, about July 12th (1898), we had been working at the fractionation of some argon-krypton residues when, after removing the vacuum vessel from the liquefying apparatus, which had been pumped out, it was noticed that a bubble of gas remained in the pump.   It seemed likely that this was only CO2, which is quite non-volatile at liquid air temperature.   The hour was late enough to have justified neglecting this bubble of gas and going home to bed.   However, it was collected as a separate fraction.'

The gas bubble was treated with potassium hydroxide to remove any CO2 and the remaining gas, about three tenths of a millilitre was introduced into a vacuum tube.   Ramsay and Travers recorded in the notebook the appearance of the spectrum from this sample: 'krypton yellow appeared very faint, the green almost absent.   Several red lines, three brilliant and equidistant, and several blue lines were seen.   Is this pure krypton, at a pressure which does not bring out the yellow and green, or a new gas?   Probably the latter!'   They noted that the most striking feature of this new gas was the beautiful blue glow from the discharge tube.

Ramsay and Travers wanted to name the new gas after its colour, but found that all the Greek and Latin roots indicating blue had long before been appropriated by organic chemists.   Instead, they settled on the name xenon, the stranger.

It took Travers and Ramsay many months before they could isolate enough xenon to determine its density.   This is not surprising since xenon is by far the least abundant of the noble gases in the atmosphere: by volume, about 1 per cent of the air is argon, 18 parts per million neon, 5 ppm helium, 1 ppm krypton and just 0.09 ppm xenon: just a couple of millilitres in an average room.   This means it is pretty expensive - a small balloon full would currently cost around £100.

Xenon currently finds its uses as the free element.    The most effective car headlamps currently available contain xenon gas at pressures of a couple of atmospheres.   Its role is to immediately provide light on switching on before some of the other components are properly vaporised.    Being so heavy, and yet chemically inert, it is used in electrostatic ion thrusters to move satellites in space.   Atoms of xenon are ionised, then accelerated to speeds of around 30 kilometres per second before being flung out the back of the engine.   These ions are forced backwards, propelling the satellite forward in the opposite direction.

Xenon-129, a stable isotope that makes up about a quarter of naturally occurring xenon, turns out to be ideal for use in magnetic resonance imaging.   Usually these instruments only detect hydrogen nuclei in water and fats - ideal for most tissue, but are of no use when looking at air spaces such as the lungs.   Not only can xenon-129 be detected when breathed into the lungs, it can also be detected dissolved in the blood allowing the functions of a working-living lung to be studied in real time.   But perhaps the strangest property of this supposedly inert gas, is that in higher concentrations it is physiologically active in the body and can act as an anaesthetic.   It is usually too expensive to use as such, but this could become more common if it can be recycled.   In April 2010, xenon made headline news, as it was first used in the treatment of a baby born with no pulse and not breathing.   By cooling the baby and treating with xenon gas to reduce the release of neurotransmitters, brain damage to the baby was avoided. Welcome to the strange world of xenon.

Meera Senthilingam 

So car headlamps, propelling satellites and saving the lives of babies. That was Cambridge University's Pete Wothers with the strange and diverse chemistry of xenon. Now next week, chemistry at the post office. 

Eric Scerri

This led to an amusing situation whereby people could try to send letters or postcards to Seaborg by using nothing but a sequence of symbols of various elements in the following order.   First of all one could write Sg for element 106 or Seaborg's name.   The second line consisted of Bk for this week's element 97 or the University at which Seaborg worked.   The third line was Cf for element 98, californium, or the state in which the university stands.   Finally, if writing from abroad, the correspondent could add Am for element 95, or americium, or the country of America to complete the address. To the credit of several postal systems around the world a handful of people did indeed succeed in getting letters and messages of congratulations to Seaborg in this cryptic fashion.

Meera Senthilingam 

And to find out how Seaborg and his team set about discovering the element in the middle of that chemical address, Berkelium, join Eric Scerri in next week's Chemistry in its element. Until then thank you for listening, I'm Meera Senthilingam.

(Promo) 

Chemistry in its element is 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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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 :
A teaching resource on Group 8 (18) - The Noble Gases, supported by video clips from the Royal Institution Christmas Lectures® 2012.
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
Description :
We discover how to extract lead from lead(II) oxide. We mix lead(II) oxide with charcoal powder and then heat the mixture using a Bunsen burner. It glows bright red as a reaction occurs and after a fe...
Learn Chemistry: Your single route to hundreds of free-to-access chemistry teaching resources.
 

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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.