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Simple Explanation:
Photoelectric Effect
Binding Energy: The energy required to eject an electron from the atom.
The relationship between an electron's energy level and its binding energy is inverse. This is because the closer an electron is to a nucleus, the stronger the attraction is between them.
Ionization Energy: The energy required to eject an electron by overcoming its binding energy.
The frequency needed to reach the ionization energy is called the threshold frequency. For most substances, UV light meets this criteria.
The photoelectric effect occurs when light with specific frequencies strikes a sheet of metal and is absorbed its electrons. If a photon carries enough energy to overcome the binding energy of the electrons, an electron will get ejected as a result.
Every element has a different absorption spectrum due to their unique electron configurations.
The photoelectrons can be detected from a machine, which can then be graphed.
Photoelectron Spectroscopy
To review on electron subshells, check out this tutorial.
Because every element has a unique electron configuration, we can determine the element of an unknown material through the photoelectric effect by detecting ejected electrons and measuring their kinetic energies that were gained from the photons.
Here is an example, showing a sample of an unknown element:
Each spike on the graph represents the detection of electrons. By fully ionizing the atoms of a sample, we can determine the electron configuration of the atoms by comparing the height of the spikes and their binding energy, which correlates with a specific subshell. Again, the relationship between an electron's energy level and its binding energy is inverse.
Subshell 1s, which is closest to the nucleus, carries two electrons max. We can then compare it with other spikes:
Here is the full electron configuration: 1s² 2s² 2p⁶ 3s² 3p¹
The element with this electron configuration is aluminum.
Binding energies vary depending on the nucleus. To compare between different substances with the same electron configuration (e.g. Na⁺ vs. Mg²⁺ vs. Al³⁺), the substance with the most protons per nucleus has the strongest binding energy. This is because more protons = more charge, increasing the force of attraction between the nucleus and electrons.
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