Inspiring Gases: Noble Gases: The Rarest Gases / Properties

Properties of the noble gases

The noble gases are unreactive gases. Apart from helium and neon, the noble gases are denser than air.

	Helium	Neon	Argon	Krypton	Xenon
Symbol	He	Ne	Ar	Kr	Xe
Atomic number	2	10	18	36	54
Relative atomic mass	4	20	40	84	131
Boiling point	4.2 K	27 K	87 K	120 K	165 K
Electronic Configuration	1s²	1s²2s²2p⁶	1s²2s²2p⁶3s²3p⁶	[Ar] 3d¹⁰4s²4p⁶	[Kr] 4d¹⁰5s²5p⁶
Key properties	Unreactive gas Liquid helium is very cold	Odourless Colourless Unreactive Gases All produce light when an electric current is applied
Major industrial applications	Filling Weather Balloons Breathing mixtures for deep sea divers Coolant for MRI Scanner magnets Welding	Advertising Signs Gas Lasers	Lightbulbs Steel Production Welding	Lighting Gas Lasers	Lighting Ion Drives for space probes
Discoverers	Pierre Janssen (1868)	William Ramsey (1898)

Sources of the noble gases

Argon is the third most abundant gas in the atmosphere, after nitrogen and oxygen, at 9340 parts per million or 0.934 per cent. The other noble gases are found in very much smaller proportions in the Earth's atmosphere (see table below). However, helium is the second most abundant element in the universe after hydrogen. About 7.2 per cent of all the atoms in the universe are helium atoms, and they form about 23 per cent of the mass of the universe. Helium is also the second most abundant element in the Sun.

Helium is formed in the Earth's crust as a result of radioactive decay (alpha particles are helium nuclei) and it can become trapped in natural gas fields. Some sources of natural gas may contain as much as 7 per cent helium. The main sources of helium are gas fields in the US, Algeria, Russia, Poland and the Middle East. The other noble gases are obtained from liquefied air using fractional distillation.

Gas	Parts per million
Argon	9340
Neon	18
Helium	5.2
Krypton	1.1
Xenon	0.1

NOBLE GASES: THE RAREST GASES

Properties of the noble gases

Sources of the noble gases