Neon

Neon, ₁₀Ne
Neon
Appearance	colorless gas exhibiting an orange-red glow when placed in an electric field
Standard atomic weight Ar°(Ne)
	20.1797±0.0006; 20.180±0.001 (abridged);
Neon in the periodic table
	fluorine ← neon → sodium
Atomic number (Z)	10
Group	group 18 (noble gases)
Period	period 2
Block	p-block
Electron configuration	[He] 2s2 2p6
Electrons per shell	2, 8
Physical properties
Phase at STP	gas
Melting point	24.56 K (−248.59 °C, −415.46 °F)
Boiling point	27.104 K (−246.046 °C, −410.883 °F)
Density (at STP)	0.9002 g/L
when liquid (at b.p.)	1.207 g/cm3
Triple point	24.556 K, 43.37 kPa
Critical point	44.4918 K, 2.7686 MPa
Heat of fusion	0.335 kJ/mol
Heat of vaporization	1.71 kJ/mol
Molar heat capacity	20.79 J/(mol·K)
Atomic properties
Oxidation states	0
Ionization energies	1st: 2080.7 kJ/mol ; 2nd: 3952.3 kJ/mol ; 3rd: 6122 kJ/mol ; (more) ;
Covalent radius	58 pm
Van der Waals radius	154 pm
	Spectral lines of neon
Other properties
Natural occurrence	primordial
Crystal structure	face-centered cubic (fcc)
Thermal conductivity	49.1×10−3 W/(m⋅K)
Magnetic ordering	diamagnetic
Molar magnetic susceptibility	−6.74×10−6 cm3/mol (298 K)
Bulk modulus	654 GPa
Speed of sound	435 m/s (gas, at 0 °C)
CAS Number	7440-01-9
History
Prediction	William Ramsay (1897)
Discovery and first isolation	William Ramsay & Morris Travers (1898)
Isotopes of neon

Neon is a chemical element; it has symbol Ne and atomic number 10. It is the second noble gas in the periodic table. It is a colorless, odorless, inert monatomic gas under standard conditions, with about two-thirds the density of air.

Neon was discovered along with krypton and xenon in 1898 as one of the three residual rare inert elements remaining in dry air after nitrogen, oxygen, argon and carbon dioxide were removed. Neon was the second of these three rare gases to be discovered and was immediately recognized as a new element from its bright red emission spectrum. The name neon is derived from the Greek word νέον, neuter singular form of νέος (neos), meaning 'new'. Neon is chemically inert, and no uncharged neon compounds are known. The known compounds of neon include ionic molecules and fragile molecules that are held together by van der Waals forces.

Most neon in the cosmos was synthesized from oxygen and helium by nuclear fusion within stars in the alpha-capture process. Although neon is a very common element in the universe and solar system (it is fifth in cosmic abundance after hydrogen, helium, oxygen and carbon), it is rare on Earth. It composes about 18.2 ppm of air by volume (this is about the same as the molecular or mole fraction) and a smaller fraction in Earth's crust. The reason for neon's relative scarcity on Earth and the inner (terrestrial) planets is that neon is highly volatile and forms no compounds to fix it to solids. As a result, it escaped from the planetesimals under the warmth of the newly ignited Sun in the early Solar System.

Neon gives a distinct reddish-orange glow when used in low-voltage neon glow lamps, high-voltage discharge tubes and neon advertising signs. The red emission line from neon also causes the well-known red light of helium–neon lasers. Neon is used in some plasma-tube and refrigerant applications but has few other commercial uses. It is commercially extracted by the fractional distillation of liquid air. Since air is the only source, neon is considerably more expensive than helium.

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