Neon

group 18 · period 2 · p-block · noble gas

Identity

Name and symbol: Neon, Ne
Atomic number: 10 protons
Position: group 18 · period 2 · p-block · noble gas
CAS number: 7440-01-9

Atomic structure

Atomic mass: 20.1797 u
Electron configuration: 1s² 2s² 2p⁶
[He] 2s²²p⁶
Electrons per shell: 2, 8
Valence electrons: 8 outer shell

isotope	mass (u)	abundance
²⁰Ne	19.992 440 18(1)	90.48 %
²¹Ne	20.993 8467(3)	0.27 %
²²Ne	21.991 3851(1)	9.25 %

natural isotopic composition, mole fraction

Physical properties

State at room temperature: Gas
Melting point: 24.56 K (-248.59 °C)
Boiling point: 27.07 K (-246.08 °C)
Density: 0.0009 g/cm3 (gas at STP, so 0.8999 g/L)
Appearance: colorless gas exhibiting an orange-red glow when placed in an electric field
Thermal conductivity: 49.1×10-3 W/(m·K)
Electrical resistivity: not in sources
Electrical conductivity: not in sources
Crystal structure: face-centered cubic
Molar heat capacity: not in sources

Chemical properties

Oxidation states: 0
Electronegativity: 4.787 (Allen Scale)
Ionisation energy: 21.565 eV
1st 2,080.7, 2nd 3,952.3, 3rd 6,122 kJ/mol
Electron affinity: 0 eV
Atomic radius: empirical 58, covalent 58, van der Waals 154 pm
Ionic radius: not in sources

Reactivity: A noble gas with a closed 2s2 2p6 shell; the most inert of all elements, with no strongly bound neutral compound ever identified.
with water: Does not react; under high pressure it only forms a clathrate hydrate in which the atoms sit unbonded in the ice cages.
with oxygen, air: Does not react.
with acids: Does not react.
with halogens: Does not react; no neon fluoride has ever been observed, and Los Alamos treats the older reports of one as questionable.

Typical compounds: not in sources

Occurrence, production and use

Crustal abundance: 5×10-3 milligrams per kilogram
Oceanic abundance: 1.2×10-4 milligrams per liter

Occurrence and sources

dissolved in seawater about 0.00012 mg/L; crustal estimate 0.005 mg/kg (Jefferson Lab figures via PubChem)
Ne in air about 18 ppm by volume of the atmosphere; the only source
crustal neon about 0.005 ppm, not recoverable

Extraction, production: Fractional distillation of liquid air, then removal of helium from the helium-neon fraction with activated charcoal
Physical separation only; neon is a minor by-product of air separation plants built for oxygen and nitrogen.

Uses

The largest use for neon gas is in advertising signs. Neon is also used to make high voltage indicators and is combined with helium to make helium-neon lasers. Liquid neon is used as a cryogenic refrigerant. Neon is highly inert and forms no known compounds, although there is some evidence that it could form a compound with fluorine.

Although neon advertising signs account for the bulk of its use, neon also functions in high-voltage indicators, lightning arrestors, wave meter tubes, and TV tubes. Neon and helium are used in making gas lasers. Liquid neon is now commercially available and is finding important application as an economical cryogenic refrigerant.

Lighting and signage: neon advertising signs, the bulk of consumption; fluorescent and indicator tubes
Electronics and instruments: high-voltage indicators, switching gear and lightning arresters; wave meter tubes and television tubes; helium-neon gas lasers, for example in barcode scanners; diving equipment
Cryogenics: liquid neon as an economical cryogenic refrigerant

Safety, toxicity

GHS classification, signal word Warning

H280 Contains gas under pressure; may explode if heated Gases under pressure
H281 Contains refrigerated gas; may cause cryogenic burns or injury Gases under pressure

Discovery and name

Discovered by: William Ramsay & Morris Travers
Discovered: 1898
First isolated: not in sources
Named by: not in sources
Origin of the name: from the Greek word νέον, meaning 'new'

Conventions

Valence electrons are counted by the usual convention: the outer shell for s- and p-block elements, ns and (n-1)d for the d-block, ns, (n-1)d and (n-2)f for the f-block. Lanthanides and actinides are placed in the f-block with no group number. Electrical conductivity is the reciprocal of the printed resistivity. Ionic radii are Shannon effective radii, six-coordinate unless noted. Where a field reads “not in sources” the value was not found; it is a gap, not a zero. Regulatory limits are the published values and change often, so check the standard in force at your site and the numbers written into your own permit before you design to them.

Data

Element records, isotopes, radii and the descriptive text come from PubChem (NCBI), the Los Alamos National Laboratory periodic table, IUPAC CIAAW and the IAEA Atomic Mass Data Center. Appearance, thermal conductivity, electrical resistivity, crystal structure, discovery and the origin of each name come from Wikipedia and Periodic-Table-JSON, used under CC BY-SA 4.0. Hazard classifications come from the ECHA C&L inventory via PubChem. Ionic radii follow R. D. Shannon (1976). The water chapters cite their own sources at the foot of each entry, and are written to the level of Snoeyink and Jenkins, Stumm and Morgan, MWH's Water Treatment and Metcalf and Eddy.