Neon
Noble gas · Period 2 · Group 18 · p-block
The red-orange glow that lit up city nights
- Atomic mass
- 20.18 u
- State at 25 °C
- Gas
- Electronegativity
- —
- Melting point
- -248.6 °C
- Boiling point
- -246 °C
- Configuration
- [He] 2s2 2p6
Neon, explained
Overview
Neon has a completely filled second shell ([He]2s2 2p6), and its electrons are held very tightly: its first ionization energy, 2081 kJ/mol, is second only to helium's. No stable neutral neon compound has ever been made, making it, with helium, the least reactive element. The forces between neon atoms are extremely weak, so neon boils at just 27 K (-246 °C). Although it is roughly the fifth most abundant element in the universe, it makes up only about 18 parts per million of Earth's air, because as a light, unreactive gas it was never trapped in rocks.
Neon's fame comes from its glow. When a high voltage passes through neon at low pressure, electrons excite the atoms, which then fall back to lower energy states and emit light at specific wavelengths, mostly in the red and orange. Each element produces its own pattern of lines, which is the basis of spectroscopy. Signs in other colours usually contain argon with a little mercury, plus phosphor coatings. Neon is also used in helium-neon lasers, in gas mixtures for the excimer lasers that pattern computer chips, and as a cryogenic refrigerant.
Discovery
William Ramsay and Morris Travers discovered neon in 1898 at University College London by slowly boiling liquefied air and examining the fractions. When they passed electricity through the new gas, it gave a brilliant crimson glow. Ramsay's 13-year-old son Willie suggested the name novum, Latin for new; Ramsay adapted it to neon, from the Greek neos. In 1910 Georges Claude displayed the first neon lamps in Paris.
- Where it’s found
- Neon is recovered as a by-product of fractional distillation of liquid air during oxygen and nitrogen production.
- What it’s used for
- Advertising signs
- Helium-neon lasers
- Cryogenic refrigeration
- Excimer laser gas
- High-voltage indicators
- In living things
- Neon has no biological role and is non-toxic.
- Safety
- Neon is inert and non-toxic; its only hazards are asphyxiation if it displaces air in a confined space and cold burns from the liquid.
How it compares
Where Neon sits among all 118 elements on the trends that shape the table.
- ElectronegativityNo data
Not measured for this element
- Ionization energy2,080kJ/mol
#2 of 104 elements with data
- Atomic radius160pm
#36 of 95 elements with data
- Electron affinity-116kJ/mol
#107 of 109 elements with data
- Density0.001g/cm³
#112 of 114 elements with data
- Melting point24.6K
#108 of 110 elements with data
- Density
- 0.9 g/L
- Atomic radius
- 160 pm
- Covalent radius
- 67 pm
- Molar heat
- —
- Appearance
- colorless gas exhibiting an orange-red glow when placed in a high voltage electric field
- Discovered by
- Morris Travers
Inside the atom
10 electrons arranged in 2 shells: 2 · 8.
Orbital diagram
1s2 2s2 2p6 · shorthand [He] 2s2 2p6
- 1s2
- 2s2
- 2p6
Each box is an orbital holding up to two electrons of opposite spin. Highlighted subshells hold the valence electrons that decide how Neon bonds.
Ionization energies
Signature reactions
The chemistry Neon is known for.
Nuclear · Fusion
Carbon burning in massive stars
In stars more than about eight times the Sun's mass, two carbon nuclei fuse to make neon-20 and an alpha particle. This is one of the main sources of the universe's neon. Later, the star burns that neon in turn as it heads toward a supernova.
Conditions: stellar core, about 600 million K
Nuclear · Fusion
Alpha capture by oxygen
An oxygen-16 nucleus captures a helium nucleus and becomes neon-20, releasing energy as a gamma ray. This step of the alpha process links the oxygen and neon made in stars. Both elements are then scattered through space when the star explodes.
Conditions: helium-burning stellar core
Physical · Plasma
Ionization in a gas discharge
In a neon tube, the applied voltage accelerates free electrons that knock electrons out of neon atoms, sustaining a glowing plasma. Other collisions merely excite atoms, which then emit red-orange light as they relax. Neon's chemical inertness means the tube can glow for decades without the gas being consumed.
Conditions: high-voltage electric discharge, low pressure
Where you’ll meet it
Neon lighting
Glass tubes of low-pressure neon glow red-orange when a high voltage is applied.
Photo: Wikimedia Commons
Las Vegas Strip
The Strip became famous for its elaborate neon signs in the mid-20th century.
Photo: Wikimedia Commons
Times Square
Neon tubing has been part of Times Square's illuminated advertising since the 1920s.
Photo: Wikimedia Commons
Helium-neon laser
In a HeNe laser, energy passed from helium to neon atoms produces a red beam at 632.8 nm.
Photo: Wikimedia Commons
Research
No research on Neon yet
When Bhavya publishes a project that studies Neon, it will be linked here.