Line Spectra

Atoms of the same element have same energy levels. Each transition releases a photon with a set amount of energy meaning the frequency and wavelength are also set. The wavelength of light is responsible for colour it is. We can analyse the light by using a diffraction grating to separate light into the colours that makes it up, called its line spectra. Each element has its own line spectra like a barcode.

To the above right are the line spectra of Hydrogen and Helium.

We can calculate the energy difference that created the colour.

If we know the energy differences for each element we can work out which element is responsible for the light and hence deduce which elements are present.

We can see that there are 6 possible transitions in the diagram to the left, A to F.

D has an energy difference of 1.9 eV or 3.04 x 10^-19 J which corresponds to a frequency of 4.59 x 10¹⁴ Hz and a wavelength of 654 nm – red.