Emission Spectra and particle-wave duality of light

When an electron jumps from a higher to a lower energy state, it emits the extra energy in a packet called a photon.

Photons can be thought of as light particles, and they have many particle-like properties. For instance, through the photoelectric effect, a photon can hit an electron and rip it from the surface of a metal as if it was a tiny ball striking another.

However, photons have wave-like properties as well. Like waves, they have a frequency and a wavelength determined by the amount of energy they carry. When an atom emits a photon of a particular energy, we can see its wavelength as a line in the electromagnetic spectrum.

The combination of all lines from the photons of all energies the atom can emit is the emission spectrum of the atom.