Noble gases
Explosive reactions
Watch some explosive results as water comes into contact with alkali metals.
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Watch a demonstration of the properties of noble gases
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Here are five of the six noble gases: helium, neon, argon, kypton and xeon. They're all colourless and transparent. Krypton and xeon form compounds only with difficulty. Helium, neon and argon don't form compounds at all.
As we descend the group in the periodic table the atomic number and relative atomic mass increases. The gasses get denser.
Helium - helium is lighter than air. Neon is just lighter. Argon and krypton - I've just got to unstick these from the anchorage... Argon and krypton are both heavier than air. And xeon, xeon is the heaviest of the lot, you've heard of a lead balloon, well this is it.
The science
The noble gases, in order of their density, are helium, neon, argon, krypton, xenon and radon. They are called noble gases because they are so majestic that, in general, they don’t react with anything. For this reason they are also known as inert gases.
The noble gases are present in the atmosphere in small amounts:
- 0.934% Argon
- 0.0018% Neon
- 0.00052% Helium
- 0.00011% Krypton
- 0.000009% Xenon
Most of the noble gases are extracted from the air, except for helium. Helium is a product of radioactive decay (the alpha particle) and is found naturally in rocks. Most of the helium used nowadays comes from natural gas, of which it comprises 7%.
Helium, the lightest, is used for filling party balloons. It is also mixed with oxygen to create a mixture that divers can breathe at depth – the helium is not very soluble in the blood so it avoids the “bends”.
Neon is probably most famous for neon signs – a tube containing neon gas through which a current is passed which causes the gas to give out light. When mixed with helium it is used to make helium-neon lasers.
Argon is used as the inert atmosphere in many light bulbs – an electric current is passed through a wire to heat it up so that it gets so hot it emits light. At these temperatures the metal would react with any oxygen present which is why an inert gas is needed.
Krypton is used to produce white light for photography – again an electrical current is passed through the gas so it emits light.
Xenon is again used in high quality lamps such as those used in lighthouses and in lasers.
Radon is a radioactive element. Radon gas is formed by decay of other radioactive elements and the concentration in the environment depends upon the types of rocks on which you live. For example, the granite in Dartmoor contains small amounts of uranium that forms radon, which can accumulate in buildings and drinking water. This leads to an increased risk of cancer.
Content last updated: 26/06/2007
Peter Taylor
A Professor of Organic Chemistry, Peter is interested in public engagement as a member of the BLAST and ISOTOPE project teams. He has been involved with many broadcast series such as The New Curiosity Shop, The Chemistry of Almost Everything, Rough Science and recently Alternative Therapies. He has written teaching materials for most areas and levels of chemistry including an MBA course in Life Sciences. He has an active research group in organosilicon chemistry.
