Neon – facts and properties

Position in the periodic table

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Occurrence and extraction

Neon is abundant in the universe, where it forms inside massive stars during carbon burning, but rare on Earth, because the young planet could not hold on to its light gases. The only practical source is the atmosphere, which contains about eighteen parts of neon per million parts of air. That is more than helium, krypton or xenon, but far less than argon. Rocks and seawater hold only traces, since neon forms no compounds and therefore never accumulates anywhere.

All commercial neon is a by-product of air separation. Large plants liquefy air and distil it into oxygen and nitrogen. Neon, helium and hydrogen do not condense even at the temperatures in the nitrogen column and collect at its top as a crude gas mixture. This is drawn off, freed of hydrogen, and separated into neon and helium by further cooling or by adsorption on activated charcoal. Only very large air separation units, typically those serving steelworks, recover neon in worthwhile amounts, so world supply has long depended on a handful of sites, several of them in Ukraine. Neon was discovered in 1898 by William Ramsay and Morris Travers in London. They isolated it from liquefied air and recognised it by the brilliant red glow it gave in a discharge tube; the name comes from the Greek neos, meaning new.

Properties and behaviour

Neon has the electron configuration [He] 2s² 2p⁶. Its outer shell holds eight electrons, a complete octet, so the atom has no reason to gain, lose or share electrons. It belongs to period 2 and group 18. Neon is generally regarded as the least reactive of all the elements: fluorides of xenon and krypton are well known, but not a single stable compound of neon exists. Only short-lived species in ion traps and at extremely low temperatures have been observed. For this reason neon is usually listed without an electronegativity.

The gas is colourless, odourless and monatomic, and with a density of 0.900 g/L it is lighter than air. It liquefies at -246.08 °C and freezes at -248.59 °C, so the temperature range over which it is liquid spans only a few degrees. Per unit volume, liquid neon can absorb far more heat than liquid helium, which makes it an efficient coolant for temperatures that liquid nitrogen cannot reach. The atomic radius is 38 pm. When a voltage is applied across a tube of low-pressure neon, the atoms are excited and emit light as they return to the ground state. The emission lines are concentrated in the red and orange part of the spectrum, giving neon signs their unmistakable colour. Neon has three stable isotopes, and the ratio of neon-20 to neon-22 helps geologists trace where gases from the Earth's mantle originate.

Uses in everyday life and technology

The best-known application is the neon sign. A glass tube is filled with neon at low pressure and a high voltage makes the gas glow. Genuine neon always glows red-orange; the other colours of illuminated signs come from argon, mercury vapour, phosphor coatings or tinted glass, though they are all loosely called neon lights. The small glow lamps in switches, voltage testers and older appliances also contain neon.

In technology, neon matters most in lasers. The helium-neon laser produces red light of very stable wavelength and was for decades the standard source in barcode scanners, surveying instruments and holography. Excimer lasers, whose gas fill consists largely of neon, emit deep ultraviolet light and are used to pattern the fine structures on silicon wafers; the semiconductor industry therefore depends on a reliable neon supply. Liquid neon serves as a cryogenic coolant in research and for certain detectors. Neon fills surge arresters in high-voltage installations and acts as a counting gas in particle detectors. In everyday life you meet neon almost exclusively as light: in vintage shop signs, in art installations and in the indicator tubes of old radios and instruments.

Quick question

Which class of substances does neon (Ne) belong to?

FAQ