Atomic emission spectra

In a nutshell

Atomic emission spectra provide good evidence for the existence of quantum shells. Here, we understand the electromagnetic spectrum, how electron excitation and energy release occurs and how evidence is provided.

The electromagnetic spectrum

Electromagnetic radiation is energy that is being transmitted in the form of waves.

The spectrum consists of the waves below:

Energy release & emission spectra

Electrons release fixed amounts of energy which can be represented by emission spectra.

Release of energy

​​1.	An atom in a ground state, with its electrons in the lowest energy level, absorbs energy.
2.	Electrons begin to move to higher energy levels. This is called excitation.
3.	Electrons then begin to return to the ground state by dropping down to lower energy levels. These energy levels have fixed values - they're discrete.
4.	​As the electrons drop down levels, they release energy as light. The frequency of light they emit is specific and can be shown on an emission spectrum. The spectra for each element is unique, as the electron arrangement is different.

Emission spectra 

• Each set of vertical lines represents an electron moving to a different energy level.
• The closer the set of lines on the spectra, the higher the frequency.
• The emission spectra of hydrogen is shown below, with three sets of lines.

Remember: Absorption occurs when electrons move up to higher energy levels. Emission occurs when electrons move down to lower energy levels.

Evidence of quantum shells

The idea of electrons orbiting the nucleus in quantum shells is supported by the emission spectra.

The principles of electron shells

1. Electrons only exist in fixed orbits in shells.
   
2. Each shell has fixed energy.
3. When electrons move between shells, electromagnetic radiation is emitted or absorbed.
4. The electromagnetic radiation exchanged will have a fixed frequency, as the shells have fixed energies.

Proof

Emission spectra has clear lines for different energy levels, this supports the rule that energy levels are discrete. There is also no intermediate phase between shells and electrons only ever exist in these fixed orbits.