Why does sodium chloride on heating with sodium vapours acquire a yellow colour?

When sodium chloride (NaCl) is heated with sodium vapors, it acquires a yellow color due to a phenomenon called sodium vapor coloration.

Here's a more detailed explanation:

Sodium Vapors: Sodium metal, when heated, vaporizes into sodium atoms. These sodium atoms have characteristic electronic transitions that can emit light when they return to lower energy levels.

Color Formation: When sodium chloride is heated in the presence of sodium vapors, the sodium atoms can get adsorbed onto the surface of the NaCl crystals. The interaction between the sodium vapors and the NaCl crystals causes the crystals to emit a yellow color.

Electronic Transitions: The yellow color is due to the emission of light in the visible spectrum (specifically around 589 nm) from the sodium atoms. When the sodium atoms are adsorbed onto the NaCl, they can influence the electronic structure of the chloride ions or the overall crystal lattice, leading to the yellow color being observed.

In summary, the yellow color is a result of the characteristic emission of sodium atoms, which are present in the vapor and interact with the sodium chloride crystals.