Neon

Neon is the chemical element with atomic number 10 and the symbol Ne. It is a colorless, odorless noble gas in group 18 that glows reddish orange when electricity passes through it at low pressure, which is the basis of the neon sign. Neon is chemically almost inert, and it is rare in Earth’s atmosphere even though it is plentiful in the universe at large.

History of neon

Neon was discovered in 1898 at University College London by William Ramsay and Morris Travers. They had been studying liquefied air and had already isolated krypton, and they were looking for lighter gases that would fit into gaps in the periodic table. By letting solid argon evaporate slowly under reduced pressure and collecting the gas that came off first, they obtained a new light gas.

When they put a sample into a spectrometer, the brilliant red glow startled them, and it is the same glow seen in neon signs today. Ramsay named the gas neon after neos, the Greek word for new. The discovery was one of several in a short period that filled out the noble gas family, which also includes helium, argon, krypton and xenon.

Properties of neon

Neon has a standard atomic weight of about 20.180 and the electron configuration [He] 2s2 2p6. Its outer shell is full, so neon will not react with any other substance under ordinary conditions. At room temperature it is a gas with a density of about 0.0009 grams per cubic centimeter. It condenses at minus 246.05 degrees Celsius and freezes at minus 248.59 degrees Celsius.

PubChem lists a van der Waals radius of 154 picometers for neon, a covalent radius of 58 picometers and a first ionization energy of 21.565 electronvolts, the energy needed to pull an electron from the atom. This is very high, which explains why neon does not form bonds readily. In a vacuum discharge tube, the gas glows reddish orange.

Neon forms no known stable compounds in ordinary conditions, according to PubChem, although there is some evidence that it could combine with fluorine. That chemical inactivity is the property that makes it safe for sealed discharge tubes and for cooling uses. It is also the reason the element was missed for so long: it left no trace in chemical reactions and showed itself only through its light.

Occurrence and production of neon

Neon is the fifth most abundant element in the universe, but it makes up only about 18 parts per million of Earth’s atmosphere. It is extracted from air by fractional distillation of liquid air, which separates gases by their boiling points. This produces a fraction containing both helium and neon, and the helium is then removed from the mixture with activated charcoal.

The crust holds only a tiny trace of neon, on the order of five millionths of a gram per kilogram, so air is the only practical source. It is one of the noble gases that is recovered as a minor by-product of air separation plants, which are run mainly to produce oxygen and nitrogen.

Uses of neon

The largest use of neon is in advertising signs. A sign filled with pure neon gives off red light, and only the red signs actually contain pure neon. Signs of other colors contain different gases or use coated tubes. Neon is also used for high-voltage indicators, switching gear, lightning arresters, wave meter tubes and diving equipment, and combined with helium it makes helium-neon lasers.

Liquid neon is an important cryogenic refrigerant, a liquid used to produce very low temperatures. According to the Royal Society of Chemistry, it has over 40 times more refrigerating capacity per unit volume than liquid helium and more than three times that of liquid hydrogen. That figure makes it attractive for some specialized cooling tasks.

How neon lighting works

A neon sign is a sealed glass tube filled with gas at low pressure, with an electrode at each end. When a high voltage is applied, the current knocks electrons around inside the gas atoms. The atoms absorb energy and then release it as light of characteristic colors, which is why pure neon looks reddish orange in the tube. Other colors come from different gases, such as argon with mercury vapor, or from tubes coated with phosphors.

The same physical idea is used to study elements in the laboratory. Each element emits a unique set of colors, called its emission spectrum, and Ramsay and Travers recognized neon from exactly such a pattern when the red glow of the new gas showed in their spectrometer.

Isotopes of neon

Neon has three stable isotopes: neon-20, neon-21 and neon-22. IUPAC data give their abundances as about 90.48 percent, 0.27 percent and 9.25 percent. Neon-20 dominates, and the proportions in samples of Earth, meteorites and the Sun give scientists clues about how the solar system formed.

Compared with its neighbors, neon sits between helium and argon in the noble gas family. Its atom is larger than helium, with a van der Waals radius of 154 picometers against 140, and its first ionization energy of 21.565 electronvolts is lower than helium but still very high. Each step down the family adds electron shells and makes the outer electrons slightly easier to remove, a trend that eventually allows the heaviest noble gases to form a few compounds.

Health and environmental effects of neon

Neon has no known biological role and is not toxic. Like helium, it can displace oxygen in enclosed spaces, which is the main safety concern when it is handled in large amounts. The gas is inert and is not known to cause any environmental harm. Neon lights themselves are safe to the public in normal use, although the glass tubes contain gas at low pressure and run at high voltage, which is why signs are installed by trained electricians.

Editorially reviewed by Specialty Digest Editorial TeamLast reviewed November 4, 2026Researched and drafted with AI assistanceReport an issue