Neon is a colorless, odorless noble gas. It is chemically inert at standard conditions and emits a bright reddish-orange glow in discharge tubes ("neon lights").
Neon has a complete valence shell with the electronic configuration \([He]2s^2 2p^6\). A filled octet gives very high ionization energy and virtually no tendency to gain or lose electrons, so Ne forms no stable compounds under ordinary conditions.
In a discharge tube, an applied electric field accelerates electrons that excite Ne atoms. When excited electrons relax to lower energy levels, they emit photons with wavelengths concentrated in the red–orange part of the spectrum (dominant lines near ~585–703 nm), giving the familiar glow.
\(E = h\nu = \tfrac{hc}{\lambda}\)
No. Pure Ne gas yields red–orange light. Other colors typically come from different gases or phosphors: Ar (blue–violet), He (peach), Kr/Xe (whitish–lavender), or Hg/argon mixtures with colored phosphor coatings. Many modern signs use LEDs rather than gas discharges.
Configuration: \([He]2s^2 2p^6\) (closed shell). Neon’s first ionization energy is among the highest of all elements, reflecting its stability. Its atomic radius is small for a noble gas due to being in Period 2.
Neon is isolated by fractional distillation of liquefied air. After removing CO2 and H2O, air is liquefied; Ne is recovered from the low-boiling fraction along with helium and hydrogen, then further purified.
Neon atoms experience only weak London dispersion forces and are monatomic and spherical, so intermolecular attractions are minimal. Thus, the temperature at which \(k_B T\) overcomes these forces is low, giving very low boiling and melting points.
In a helium–neon laser, collisions transfer energy from excited He to Ne, populating Ne’s metastable levels. Stimulated emission then occurs, commonly at \(\lambda = 632.8\,\text{nm}\) (red). The role of He is to efficiently pump Ne’s lasing states.
Under standard conditions, Ne does not form stable compounds due to its closed-shell configuration. A few matrix-isolated or highly transient species have been reported at extremely low temperatures, but they are not stable, isolable compounds in the usual sense.
Use the photon relation:
\(E = h\nu = \dfrac{hc}{\lambda}\)
For a bright red Ne line near \(\lambda \approx 640\,\text{nm}\), \(E\approx 3.1\times10^{-19}\,\text{J}\) per photon (about 1.9 eV). Summed over many photons, this yields the visible glow in discharge tubes.