The Noble Gases

Besides the major components nitrogen and oxygen, the air contains smaller amounts of elements belonging to a special group of the periodic table: The noble gases. In everyday life they are known from gas-filled balloons, colourful neon lights and xenon headlights.

Which Elements Belong to the Noble Gases?

Helium, neon, argon, krypton, xenon and radon form the 8th main group of the periodic table and are called noble gases. All of them are colourless, odourless, very slow reacting gases, which occur as a single atom and possess a very low melting and boiling point. Radon is radioactive.

How Noble Are They Really?

They are termed noble gases, because these elements usually don’t form compounds or react with other elements. This is because their outermost shell is already fully occupied with eight electrons, and so they are not inclined to gain or lose any electrons.
For a long time it was believed that noble gases do not form any compounds at all. In the meantime, scientists succeeded in producing noble gas compounds under special conditions. So the noble gases are not as 'noble' as they were said to be, but nevertheless extremely slow to react.
As a result, the 8th main group was only discovered very late, namely at the end of the 19th Century.

Where Do Noble Gases Occur?

With the exception of radon, all noble gases are contained in the air in small amounts – around a total of 1 percentage by volume. They are gained by fractioned distillation of liquefied air.
The most abundant noble gas in the air is argon with a 0.9 percentage by volume.
Helium can be found in some natural gas reservoirs. Large amounts of helium exist on the sun, where it is formed by nuclear fusion of hydrogen.
The short-lived radon is generated by radioactive fission. In some places - near Bad Gastein, Austria, for example - it escapes from the rocks in larger quantities.

What Are Noble Gases Used for?

Helium is a very lightweight gas and is used for filling balloons and airships. When mixed with oxygen, it serves as breathing gas for scuba divers. As helium has a different density than air, the voice sounds distorted when helium is inhaled. Helium only becomes liquid at very low temperatures near absolute zero. Liquid helium is used as a low-temperature refrigerant. Due to their unresponsiveness, noble gases - especially argon- are used as shielding gases in situations where the oxygen in the air would lead to unwanted oxidation reactions: during welding, in light bulbs and during air-sensitive reactions in a chemical laboratory.

When enclosed in a glass tube and subjected to high voltage, noble gases emit visible light. Such gas discharge tubes are used for illuminated ads. The colour of the light depends on the gas used for filling: Helium shines yellow, neon (in the so-called neon lights) shines red, argon blue, krypton violet and xenon blue-white. The especially bright xenon headlights in cars are gas discharge tubes as well.

A mixture of helium and neon is used to manufacture laser