Some elements exist in several different structural forms, called allotropes. Each allotrope has different physical properties.

For more information on the Visual Elements image see the Uses and properties section below.



A vertical column in the periodic table. Members of a group typically have similar properties and electron configurations in their outer shell.

A horizontal row in the periodic table. The atomic number of each element increases by one, reading from left to right.

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 (s), principal (p), diffuse (d), and fundamental (f).

Atomic number
The number of protons in an atom.

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

Melting point
The temperature at which the solid–liquid phase change occurs.

Boiling point
The temperature at which the liquid–gas phase change occurs.

The transition of a substance directly from the solid to the gas phase without passing through a liquid phase.

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.

Atoms of the same element with different numbers of 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.

Fact box

Group 18  Melting point −111.75°C, −169.15°F, 161.4 K 
Period Boiling point −108.099°C, −162.578°F, 165.051 K 
Block Density (g cm−3) 0.005366 
Atomic number 54  Relative atomic mass 131.293  
State at 20°C Gas  Key isotopes 132Xe 
Electron configuration [Kr] 4d105s25p6  CAS number 7440-63-3 
ChemSpider ID 22427 ChemSpider is a free chemical structure database


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.


The description of the element in its natural form.

Biological role

The role of the element in humans, animals and plants.

Natural abundance

Where the element is most commonly found in nature, and how it is sourced commercially.

Uses and properties

Image explanation
The ‘electro-flash’ icon reflects the use of the gas in camera flash technology. This is usually a tube filled with xenon gas, with electrodes at each end and a metal trigger plate at the middle of the tube.
A colourless, odourless gas. It is very unreactive.
Xenon is used in certain specialised light sources. It produces a beautiful blue glow when excited by an electrical discharge. Xenon lamps have applications as high-speed electronic flash bulbs used by photographers, sunbed lamps and bactericidal lamps used in food preparation and processing. Xenon lamps are also used in ruby lasers.

Xenon ion propulsion systems are used by several satellites to keep them in orbit, and in some other spacecraft.

Xenon difluoride is used to etch silicon microprocessors. It is also used in the manufacture of 5-fluorouracil, a drug used to treat certain types of cancer.
Biological role
Xenon has no known biological role. It is not itself toxic, but its compounds are highly toxic because they are strong oxidising agents.
Natural abundance
Xenon is present in the atmosphere at a concentration of 0.086 parts per million by volume. It can also be found in the gases that evolve from certain mineral springs. It is obtained commercially by extraction from liquid air.
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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.

Atomic radius, non-bonded
Half of the distance between two unbonded atoms of the same element when the electrostatic forces are balanced. These values were determined using several different methods.

Covalent radius
Half of the distance between two atoms within a single covalent bond. Values are given for typical oxidation number and coordination.

Electron affinity
The energy released when an electron is added to the neutral atom and a negative ion is formed.

Electronegativity (Pauling scale)
The tendency of an atom to attract electrons towards itself, expressed on a relative scale.

First ionisation energy
The minimum energy required to remove an electron from a neutral atom in its ground state.

Atomic data

Atomic radius, non-bonded (Å) 2.16 Covalent radius (Å) 1.36
Electron affinity (kJ mol−1) Not stable Electronegativity
(Pauling scale)
Ionisation energies
(kJ mol−1)


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. Uncombined elements have an oxidation state of 0. The sum of the oxidation states within a compound or ion must equal the overall charge.


Atoms of the same element with different numbers of neutrons.

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

Oxidation states and isotopes

Common oxidation states 6, 4, 2
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  124Xe 123.906 0.0952 > 1017 β-β- 
  126Xe 125.904 0.089
  128Xe 127.904 1.9102
  129Xe 128.905 26.4006
  130Xe 129.904 4.071
  131Xe 130.905 21.2324
  132Xe 131.904 26.9086
  134Xe 133.905 10.4357 > 1.1 x 1016 β-β- 
  136Xe 135.907 8.8573 > 8.5 x 1021 β-β- 


Data for this section been provided by the British Geological Survey.

Relative supply risk

An integrated supply risk index from 1 (very low risk) to 10 (very high risk). This is calculated by combining the scores for crustal abundance, reserve distribution, production concentration, substitutability, recycling rate and political stability scores.

Crustal abundance (ppm)

The number of atoms of the element per 1 million atoms of the Earth’s crust.

Recycling rate

The percentage of a commodity which is recycled. A higher recycling rate may reduce risk to supply.


The availability of suitable substitutes for a given commodity.
High = substitution not possible or very difficult.
Medium = substitution is possible but there may be an economic and/or performance impact
Low = substitution is possible with little or no economic and/or performance impact

Production concentration

The percentage of an element produced in the top producing country. The higher the value, the larger risk there is to supply.

Reserve distribution

The percentage of the world reserves located in the country with the largest reserves. The higher the value, the larger risk there is to supply.

Political stability of top producer

A percentile rank for the political stability of the top producing country, derived from World Bank governance indicators.

Political stability of top reserve holder

A percentile rank for the political stability of the country with the largest reserves, derived from World Bank governance indicators.

Supply risk

Relative supply risk Unknown
Crustal abundance (ppm) 0.00003
Recycling rate (%) Unknown
Substitutability Unknown
Production concentration (%) Unknown
Reserve distribution (%) Unknown
Top 3 producers
  • Unknown
Top 3 reserve holders
  • Unknown
Political stability of top producer Unknown
Political stability of top reserve holder Unknown


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

A measure of the stiffness of a substance. 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

A measure of how difficult it is to deform a material. It is given by the ratio of the shear stress to the shear strain.

Bulk modulus

A measure of how difficult it is to compress a substance. It is given by the ratio of the pressure on a body to the fractional decrease in volume.

Vapour pressure

A 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)
158 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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Listen to Xenon Podcast
Transcript :

Chemistry in its element: xenon


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.


Chemistry in its element is brought to you by the Royal Society of Chemistry and produced by There's more information and other episodes of Chemistry in its element on our website at

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Visual Elements images and videos
© Murray Robertson 1998-2017.



W. M. Haynes, ed., CRC Handbook of Chemistry and Physics, CRC Press/Taylor and Francis, Boca Raton, FL, 95th Edition, Internet Version 2015, accessed December 2014.
Tables of Physical & Chemical Constants, Kaye & Laby Online, 16th edition, 1995. Version 1.0 (2005), accessed December 2014.
J. S. Coursey, D. J. Schwab, J. J. Tsai, and R. A. Dragoset, Atomic Weights and Isotopic Compositions (version 4.1), 2015, National Institute of Standards and Technology, Gaithersburg, MD, accessed November 2016.
T. L. Cottrell, The Strengths of Chemical Bonds, Butterworth, London, 1954.


Uses and properties

John Emsley, Nature’s Building Blocks: An A-Z Guide to the Elements, Oxford University Press, New York, 2nd Edition, 2011.
Thomas Jefferson National Accelerator Facility - Office of Science Education, It’s Elemental - The Periodic Table of Elements, accessed December 2014.
Periodic Table of Videos, accessed December 2014.


Supply risk data

Derived in part from material provided by the British Geological Survey © NERC.


History text

Elements 1-112, 114, 116 and 117 © John Emsley 2012. Elements 113, 115, 117 and 118 © Royal Society of Chemistry 2017.



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