Absorption and Emission

Altough the animation above is not the real representation of an atom, the mechanism of the absorption and the emission of a photon is correct.

The electron is the red sphere and the nucleus the blue one. Photons are represented by the coming yellow waves. The electron absorbs a photon and it is excited to a higher energy orbital.

Note that at the time electron emits the photon it returns to its previous orbital. The two photons carry the same amount of energy. To find this energy we have to subtract the energy between the first and the second orbital.