Why do atoms emit or absorb light of specific wavelengths?

Question

Owen Atkinson · Accepted Answer

The electrons in an atom can only occupy certain allowed energy levels. When an electron drops from a higher energy level to a lower one, the excess energy is emitted as a photon of light, with its wavelength dependent on the change in electron energy.

Classical physics predicted that a negatively charged electron would fall into a positively charged nucleus, emitting a continuous spectrum of light as it did so. This is obviously not the case, as if it were, there would be no stable atoms. It was later discovered that this did not occur because electrons can only occupy discrete energy levels within the atom. This was one of the early results of quantum mechanics. When an electron drops from a higher energy level to a lower one, the excess energy is emitted as a photon of light. The wavelength, #lamda# of the photon is inversely proportional to the change in electron energy: #lambda= (c times h) / text(change in electron energy)# where h is Planck's constant and c is the speed of light in a vacuum. When an electron falls to a lower energy level, only specific energy levels are permitted, which means that only specific transitions are possible, and as a result, only specific wavelengths are emitted; on the other hand, when an atomic electron absorbs a photon, it can be promoted to a higher energy level, again because only specific transitions are permitted, which means that only specific wavelengths can be absorbed.

Ivy Allen · Answer

undefined Atoms emit or absorb light at specific wavelengths due to electron transitions between energy levels. These transitions are characteristic of each element and are governed by quantum mechanics. An electron that moves from a higher energy level to a lower one emits light at specific wavelengths; on the other hand, an electron that absorbs energy moves to a higher energy level and absorbs light at specific wavelengths.