Band spectrum and line spectrum

[smart_worker]

why do the atoms in excited state alone could emit line spectra?can't they emit when they are not in gaseous state?

why only molecules can emit band spectra?can't atoms emit them

 

[Drakkith]

An isolated atom, such as one in a gaseous state, has only its atomic energy levels available to accept or give up energy. Since these energy levels are discrete, the light emitted by the atoms will also be in discrete wavelengths.

Atoms bound in molecules or in a liquid state have more energy levels to accept or give up energy from. As such, the light they emit will be over a much broader range. In an everyday solid or liquid the amount of energy levels is so large that light is emitted over the entire spectrum.