'Noble Gases' is the most common designation for the elements in the rightmost group (group 0, group VIII or group 18 depending on which nomenclature is being used) of The Periodic Table of the Elements. The commonly found designations 'inert gases' or 'rare gases' are somewhat misleading. Firstly, they are not inert in a strict sense. And secondly, they are not rare. Argon, for example, makes up almost one per cent of the atmosphere, and helium is the second most common element in the universe.

For a number of complicated reasons, which involve serious Quantum Mechanics, and electron filling rules for atomic shells and orbitals, these elements have many properties in common. This includes their extremely low chemical reactivity. For example, the Noble Gases are not flammable and are very unreactive when a chemical reaction is applied. This low reactivity is the reason why these elements are termed 'noble.' Or possibly their arrogant behaviour - as seen from a chemical perspective, these gases do not get together with other elements, similar to many 'noble' aristocrats. Some pieces of data on the noble gases are collected in the following table:

Some Data for the Noble Gases Helium Neon Argon Krypton Xenon Radon Symbol He Ne Ar Kr Xe Rn Atomic number 2 10 18 36 54 86 Atomic weight [u] 4.001602 20.1797 39.948 83.80 131.29 (222.02) %Vol. in air 0.000524 0.001818 0.934 0.000114 0.0000087 6 x 10-18 Boiling point [°C] -268.9 -246.08 -185.9 -153.2 -108.0 -61.7 Melting point [°C] (-272.2°C) -248.59 -189.3 -157.4 -111.76 -71 Inversion temperature [°C] -233 -3 450 1000 1700 - Critical temperature [°C] -267.9 -228.7 -122.3 -63.8 16.6 105 Critical pressure [bar] 2.26 26.9 48.3 54.3 57.6 62 Enthalpy of evaporation [kJ/mol] 0.0812 1.732 6.518 9.029 12.635 18.096 Gas density [g/l] 0.1785 0.89990 1.7837 3.733 5.887 9.73 Liquid density [g/ml] 0.125 1.207 1.400 2.413 3.057 4.4 Atomic radius [pm] 93 131 174 189 209 214 Colour of light

in a gas discharge tube yellow red purple lime turquoise - 1st ionisation energy [eV] 24.586 21.563 15.759 13.998 12.130 10.75 2nd ionisation energy [eV] 54.41 40.96 27.62 24.35 21.20 -

Noble Gases: Yesterday and Today

One consequence of the aforementioned Noble Gases' low reactivity was that these elements were discovered and isolated only relatively late. The first person to actually isolate and note the presence of Noble Gases - however, without going into further details - was Henry Cavendish (1731-1810 chemistry weirdo and 'discoverer' of hydrogen) in 1785. The real 'discovery' of the Noble Gases, their isolation and proper characterisation took place between 1890 and 1900. A key figure in the process of discovering, isolating and characterising the gases was a chap called William Ramsay, who in the end became 'nobel' for the noble stuff (more details are in The History Around the Noble Gases).

All Noble Gases are widely used in industrial applications and in scientific research. With the exception of radon they are all used as luminescent gases, e.g. in lasers or in neon lighting. They are also widely used as protective gases, eg in semiconductor manufacturing. All the gases, except helium and radon, can be obtained from the fractional distillation of liquid air. Helium (originating from radioactive decay) is not held in the atmosphere by the earth's gravity. However, it is found sealed or trapped deep inside the earth, commonly along with gas and petroleum, from where it is extracted. Helium is the most well-known and most widely used Noble Gas, eg to fill balloons and dirigibles. Radon is very difficult to obtain as a pure gas, since it is not a stable element. Even so, in the past it has found uses as a radioactive tracer gas for medical applications.