Emission spectra
If an electron is in an excited state it can return to a lower energy level. When it does this, it loses energy.
The amount of energy it loses will be equal to the difference in the energy levels it moves between. This energy is released as a photon.
The energy of the photon can be worked out using the equation
If an electron moves from level \(E_{2}\) to \(E_{1}\) the energy of the photon can be worked out using the following:
\(E=hf=E_{2}-E_{1}\)
For this relationship:
- \(E\) is the energy of the photon
- \(h\) is Planck's constant
- \(f\) is the frequency of light produced
As the energy levels have different values, each of the possible electron transitions within an atom will produce a photon with a different energy.
This means that each electron transition will produce a photon of a different frequency and hence a different colour.
This causes line emission spectra to be produced, as shown below.
This is not a continuous spectrum as only light of specific frequencies and specific colours are produced.
Different types of atoms have different energy levels. As a result each produces photons with different energy and so the line spectra for different elements will be different.
This means that line spectra can be used to identify elements.
Continuous spectra are produced by electrons being shared between many atoms, giving a huge range of possible frequencies, as shown below.