Atomic emission spectra
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Explainer Video
Summary
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.  Energy is emitted as light (1) as the electron drops to a lower energy level (2) |
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
- Electrons only exist in fixed orbits in shells.
- Each shell has fixed energy.
- When electrons move between shells, electromagnetic radiation is emitted or absorbed.
- 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.
FAQs - Frequently Asked Questions
Are energy levels discrete or continuous?
Emission spectra has clear lines for different energy levels, this supports the rule that energy levels are discrete.
What is absorption and emission?
Absorption occurs when electrons move up to higher energy levels. Emission occurs when electrons move down to lower energy levels.
What provides evidence for quantum shells?
Atomic emission spectra provide good evidence for the existence of quantum shells.