Electron Work Function
Definition and meaning of Electron Work Function in chemistry.
Electron work function is the minimum energy needed to remove an electron from the surface of a solid, usually a metal, to a point just outside that surface with zero kinetic energy. It is also called the photoelectric work function because it sets the energy threshold for the photoelectric effect.
In more detail
The work function, symbol Φ, is a surface property rather than a bulk property: it depends on the material, the crystallographic face exposed, and surface conditions such as adsorbed gases or contamination. In the photoelectric effect, Einstein's equation hν = Φ + KE(max) shows that a photon can eject an electron only if its energy hν exceeds Φ, with any surplus energy becoming the electron's kinetic energy; the corresponding minimum frequency is the threshold frequency, ν0 = Φ/h. Work function values also govern thermionic emission and the contact potential difference between dissimilar metals in contact.
Key facts
| Symbol | Φ (phi) |
|---|---|
| Typical unit | electronvolt (eV) |
| Typical range | about 2-5 eV for metals (e.g., sodium ≈ 2.3 eV, platinum ≈ 5.65 eV) |
| Field | Physical Chemistry |
Sodium metal has a work function of about 2.3 eV. Using λ0 = hc/Φ, this corresponds to a threshold wavelength near 540 nm, so only light of that wavelength or shorter (green, blue, or ultraviolet) can eject photoelectrons from a clean sodium surface; longer-wavelength (redder) light, no matter how intense, cannot.
Frequently asked questions
How is work function related to the photoelectric effect?
Einstein's photoelectric equation, hν = Φ + KE(max), shows that photoemission occurs only when the photon energy hν exceeds the work function Φ; the minimum frequency that satisfies this is the threshold frequency ν0 = Φ/h.
Is the work function the same as ionization energy?
No. Ionization energy removes an electron from an isolated gas-phase atom or ion, while the work function removes an electron from the surface of a bulk solid, and the two values are generally different even for the same element.