AP Chemistry: The Photoelectric Effect – by Daniel
(Biology and Chemistry tutor at The Edge Learning Center)
Boost your AP Chemistry bit by bit!
The Photoelectric Effect
For AP Chemistry, we should be familiar with the photoelectric effect – when electromagnetic energy is used to “knock-out” an electron(s) from a metal (see Figure 1 below). When photons (packets of energy) hit a given metal, their energy is transferred to the valence electrons i.e. electrons in the outermost energy shell of the metal. This results in two possible outcomes: if the photon has enough energy it can enable the metal electrons to overcome the attractive forces which hold them together in the metal lattice, thereby ejecting a photo-electron; if the photon energy is not enough to ionize an electron, the electrons will be excited to higher energy levels within atomic orbitals. We should understand the following qualitative features to comprehend this phenomenon:
1. Photons with high-frequency radiation have high energies and can therefore “knock” electrons out of a metal.
2. For electrons in the metal, energy must be absorbed to allow electrons to be promoted to higher atomic orbital energy levels.