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Xenon was discovered by William Ramsay ( [link] ) and Morris Travers ( [link] ) on July 12, 1898, shortly after their discovery of krypton and neon.


Radon was the fifth radioactive element to be discovered after uranium, thorium, radium and polonium. Discovered in 1900 by Friedrich Dorn ( [link] ) after he noticed that radium compounds emanate a radioactive gas that he named Radium Emanation ( Ra Em ). Prior to these experiments, in 1899, Pierre and Marie Curie ( [link] ) observed that the gas emitted by radium remained radioactive for a month. Later that year, Ernest Rutherford ( [link] ) noticed variations when trying to measure radiation from thorium oxide. In 1901, he demonstrated that the emanations are radioactive, but credited the Curies for the discovery of the element.

German physicist Friedrich Ernst Dorn (1848 - 1916).
Pierre (1859 - 1906) and Marie Skłodowska-Curie (1867 - 1934) in their Paris laboratory.
British-New Zealand chemist and physicist Ernest Rutherford, 1 st Baron Rutherford of Nelson, OM, FRS (1871 - 1937).


The abundance of the Noble gases is given in [link] .

Abundance of Group 18 elements.
Element Terrestrial abundance (ppm)
He 8 x 10 -3 (Earth’s crust), 4 x 10 6 (sea water), 5 (atmosphere)
Ne 70 x 10 -3 (Earth’s crust), 0.2 (sea water), 18 (atmosphere)
Ar 1.2 (Earth’s crust), 0.45 (sea water), 0.93 x 10 4 (atmosphere)
Kr 10 x 10 -6 (Earth’s crust), 80 x 10 -6 (sea water), 1 (atmosphere)
Xe 2 x 10 -6 (Earth’s crust), 100 x 10 -6 (sea water), 90 x 10 -3 (atmosphere)


The naturally abundant isotopes of the Group 18 elements are listed in [link] . All of the isotopes of radon are radioactive.

Abundance of the non-synthetic isotopes of the Group 18 elements.
Isotope Natural abundance (%)
Helium-3 0.000137
Helium-4 99.999863
Neon-20 90.48
Neon-21 0.27
Neon-22 9.25
Argon-36 0.337
Argon-86 0.063
Argon-40 99.600
Krypton-78 0.35
Krypton-80 2.25
Krypton-81 trace
Krypton-82 11.6
Krypton-83 11.5
Krypton-84 57
Krypton-86 17.3
Xenon-124 0.095
Xenon-126 0.089
Xenon-128 1.91
Xenon-129 26.4
Xenon-130 4.07
Xenon-131 21.2
Xenon-132 26.9
Xenon-134 10.4
Xenon-136 8.86
Radon-222 trace

Unlike most elements, helium's isotopic abundance varies greatly by origin, due to the different formation processes. The most common isotope, 4 He, is produced on Earth by a decay of heavier radioactive elements. It was also formed in enormous quantities during the Big Bang .

Naturally occurring 40 K with a half-life of 1.25 × 10 9 years, decays to stable 40 Ar (11.2%) by electron capture and positron emission, and also to stable 40 Ca (88.8%) via beta decay. These properties and ratios are used to determine the age of rocks.

With a half-life of 230,000 years 81 Kr is used for dating 50,000 - 800,000 year old groundwater. 85 Kr is an inert radioactive noble gas with a half-life of 10.76 years. It is produced in nuclear bomb testing and nuclear reactors. 85 Kr is released during the reprocessing of fuel rods from nuclear reactors.

Industrial production of the elements

Helium is extracted by fractional distillation from natural gas, which contains up to 7% helium. Since helium has a lower boiling point than any other element, low temperature and high pressure are used to liquefy nearly all the other gases. The resulting helium gas is purified by successive exposures to lowering temperatures. A final purification step with activated charcoal results in 99.995% pure Grade-A helium.

Argon is produced industrially by the fractional distillation of liquid air, a process that separates liquid nitrogen, which boils at 77.3 K, from argon, which boils at 87.3 K and oxygen, which boils at 90.2 K. Xenon is obtained commercially as a byproduct of the separation of air into oxygen and nitrogen.

Physical properties

The physical properties of the Group 18 elements are given in [link] .

Selected physical properties of the Group 18 elements.
Element Mp (°C) Bp (°C)
He -272.20 -268.93
Ne -248.59 -246.08
Ar -189.35 -185.85
Kr -157.36 -153.22
Xe -111.7 -108.12
Rn -71.15 -61.85

All of the Noble gases show characteristic spectral lines ( [link][link] ).

Spectral lines of helium.
Spectral lines of neon.
Spectral lines of argon.
Spectral lines of krypton.
Spectral lines of xenon.

Compounds of the group 18 elements.

Only a few hundred noble gas compounds have been formed. Neutral compounds of helium and neon have not been formed, while xenon, krypton, and argon have shown only minor reactivity. The reactivity follows the order:

Xenon compounds are the most numerous of the noble gas compounds. Oxidation states of +2, +4, +6, and +8 with electronegative elements, e.g., XeF 2 , XeF 4 , XeF 6 , XeO 4 , and Na 4 XeO 6 . Compounds of xenon bound to boron, hydrogen, bromine, iodine, beryllium, sulphur, titanium, copper, and silver have also been observed but only at low temperatures in noble gas matrices, or in supersonic noble gas jets.

Although radon is more reactive than xenon it should form chemical bonds more easily than xenon, however, due to the high radioactivity and short half-life of radon isotopes, only a few fluorides and oxides of radon have been formed.

Krypton is less reactive than xenon, and oxidation states are generally limited to +2, KrF 2 . Compounds in which krypton forms a bond to nitrogen and oxygen are only stable below -60 °C and -90 °C, respectively. Krypton atoms chemically bound to other nonmetals (hydrogen, chlorine, carbon) as well as some late transition metals (copper, silver, gold), but only at low temperatures in noble gas matrices, or in supersonic noble gas jets. Similar conditions were used to obtain the first compounds of argon.

Noble gases also form non-covalent compounds, for example clathrates that consist of an atom trapped within cavities of crystal lattices of organic and inorganic compounds. Noble gases can form endohedral fullerene compounds, in which the noble gas atom is trapped inside a fullerene molecule ( [link] ).

A skeletal structure of He@C 60 .


  • L. Pauling, J. Am. Chem. Soc. , 1933, 55 , 1895.
  • M. Saunders, H. A. Jiménez-Vázquez, R. J. Cross, and R. J. Poreda, Science , 1993, 259 , 1428.

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
analytical skills graphene is prepared to kill any type viruses .
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
waht is hydrating power of lithium carbonates
Mahar Reply

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Source:  OpenStax, Chemistry of the main group elements. OpenStax CNX. Aug 20, 2010 Download for free at http://cnx.org/content/col11124/1.25
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